Achintya Haldar

Interests

Teaching

Courses related to structures and risk & reliability

Research

Conducts research exclusively on risk and reliability applied to many branches of engineering.

Courses

Scholarly Contributions

Books

• Haldar, A. (2017). Risk Based Damage-Tolerant Seismic Design of Structures -- A New Paradigm. Indian Institute of Technology – Guwahati, India.
• Haldar, A. (2013). Health Assessment of Engineered Structures: Bridges, Buildings and Other Infrastructures. New Jersey: World Scientific Publishing Co.
• Haldar, A., & Mahadevan, S. (2000). Reliability assessment using stochastic finite element analysis. John Wiley & Sons.

Chapters

• Gaxiola-Camacho, J. R., Azizsoltani, H., Haldar, A., & Vazirizade, S. M. (2019). Chapter 13 - Novel Concepts for Reliability Analysis of Dynamic Structural Systems. In Handbook of Probabilistic Models(pp 305-346). Butterworth-Heinemann, Elsevier. doi:https://doi.org/10.1016/B978-0-12-816514-0.00013-8
• Haldar, A. (2019). Chapter 1 - Fundamentals of Reliability Analysis. In Handbook of Probabilistic Models(pp 1-35). Butterworth-Heinemann, Elsevier. doi:https://doi.org/10.1016/B978-0-12-816514-0.00001-1
• Haldar, A. (2019). Uncertainty Modeling for Nonlinear Dynamic Systems----Loadings Applied in Time Domain. In Risk Based Technologies(pp 49--64). Springer, Singapore.
• Haldar, A., & Al-Hussein, A. .. (2016). Prognostics and Structural Health Assessment Using Uncertain Measured Response Information. In Current Trends in Reliability, Availability, Maintainability and Safety, Edited by U. Kumar, A. Ahmadi, A. K. Verma, and P. Varde(pp 165--186). Springer International Publishing.
• Haldar, A. (2015). Structural Reliability Estimation for Seismic Loading. In Springer Reference, http://www.springerreference.com/index/chapterdbid/382024, 2015, DOI 10.1007/978-3-642-36197-5_277-1.
• Das, A. K., & Haldar, A. (2013). Chapter 6 – A Novel Health Assessment Method for Large Three Dimensional Structures. In Health Assessment of Engineered Structures: Bridges, Buildings and Other Infrastructures(pp 149-178). New Jersey: World Scientific Publishing Co.
• Das, A. K., & Haldar, A. (2012). Structural Health Assessment Using Extended Kalman Filter. In Advances in Mathematics Research,ISBN 978-1-61324-928-4(pp 397-442). New York: Nova Science Publishers.

Journals/Publications

• Al-Hussein, A., & Haldar, A. (2019). Condition Assessment of Civil Structures under Earthquake Excitation. Journal of Aerospace Engineering, ASCE, 32(1), 12. doi:10.1061/(ASCE)AS.1943-5525.0000943
• Azizsoltani, H., Gaxiola-Camacho, J. R., Villegas-Mercado, F. J., & Haldar, A. (2019). Discussion of “State-of-the-Art Review on Seismic Design of Steel Structures” by Chia-Ming Uang and Michel Bruneau. Journal of Structural Engineering, 145(5), 07019001.
• Haldar, A., Vazirizade, S. M., & Gaxiola-Camacho, J. R. (2019). Uncertainty quantification of sea waves - an improved approach. Journal of Oceanography & Fisheries, 9(5): 555775. doi:http://dx.doi.org/10.19080/OFOAJ.2019.09.555775
• Reyes-Salazar, A., Bojorquez, E., Bojorquez, J., Valenzuela-Beltran, F., & Haldar, A. (2019). Seismic Reduction Factor Evaluation And Its Components For Steel Buildings Undergoing Nonlinear Deformations. Current Science, 116(11), 1850-1860. doi:doi: 10.18520/cs/v116/i11/1850-1860
• Al-Hussein, A., & Haldar, A. (2018). Nonlinear System Identification from Noisy Measurements. International Journal of Structural Engineering (IJSTRUCTE), 9(2), 155-173.
• Azizsoltani, H., & Haldar, A. (2018). Reliability Analysis of Lead-Free Solders In Electronic Packaging Using A Novel Surrogate Model And Kriging Concept. Journal of Electronic Packaging, ASME, 140(4), 041003-1 to 11. doi:doi:10.1115/1.4040924
• Azizsoltani, H., Gaxiola-Camacho, J. R., & Haldar, A. (2018). Site-Specific Seismic Design of Damage Tolerant Structural Systems Using a Novel Concept. Bulletin of Earthquake Engineering. doi:https://doi.org/10.1007/s10518-018-0329-5
• Gaxiola-Camacho, J. R., Haldar, A., Reyes-Salazar, A., Valenzuela-Beltran, F., Vazquez-Becerra, G., & Vazquez-Hernandez, A. (2018). Alternative Reliability-Based Methodology For Evaluation Of Structures Excited By Earthquakes. Earthquakes and Structures, An International Journal, 14(4).
• Gaxiola-Camacho, J., Haldar, A., Azizsoltani, H., Valenzuela-Beltran, F., & Reyes-Salazar, A. (2018). Performance-Based Seismic Design of Steel Buildings Using Rigidities of Connections. ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering, 4(1), DOI: 10.1061/AJRUA6.0000943.
• Tran, Q. H., Huh, J., Nguyen, V. B., Haldar, A., Kang, C., & Hwang, K. M. (2018). Comparative Study of Nonlinear Static and Time History Analyses of Typical Korean STS Container Cranes. Special Issue on Advances in Seismic Performance Assessment and Improvement of Structures, Advances in Civil Engineering, 2018, 13. doi:https://doi.org/10.1155/2018/2176894
• Al-Hussein, A. .., & Haldar, A. (2017). Complexities in Assessing Structural Health of Civil Infrastructures. Compexity, 2017(Article ID 2623805), doi--10.
• Al-Hussein, A., & Haldar, A. (2017). Structural Damage Prognosis of Three-Dimensional Large Structural Systems. Structure and Infrastructure Engineering, 13(12), 1596–1608. doi:https://doi.org/10.1080/15732479.2017.1304430
• Azizsoltani, H., & Haldar, A. (2017). Intelligent Computational Schemes for Designing more Seismic Damage-Tolerant Structures. Journal of Earthquake Engineering, http--dx.
• Gaxiola-Camacho, J. R., Azizsoltani, H., Villegas-Mercado, F. J., & Haldar, A. (2017). A novel reliability technique for implementation of Performance-Based Seismic Design of structures. Engineering Structures, 142, 137--147.
• Huh, J., Tran, Q. H., Haldar, A., Park, I., & Ahn, J. (2017). Seismic Vulnerability Assessment of a Shallow Two-Story Underground RC Box Structure. Applied Sciences, 7(735), doi--10.
• Mercado, F., Azizsoltani, H., Gaxiola-Camacho, J. R., & Haldar, A. (2017). Seismic Reliability Evaluation of Structural Systems for Different Soil Conditions. International Journal of Geotechnical Earthquake Engineering (IJGEE), 8(2), 23--38. doi:10.4018/IJGEE.2017070102
• Reyes-Salazar, A. .., Llanes-Tizoc, M. D., Boj'orquez, E., Luz, R., Lopez-Barraza, A. .., & Haldar, A. (2017). Strength Or Force Reduction Factors For Steel Buildings: MDOF Vs SDOF Systems. Journal of Vibroengineering, 19(4), 2680--2702.
• Tran, Q. H., Han, D., Kang, C., Haldar, A., & Huh, H. (2017). Effects of Ambient Temperature and Relative Humidity on Subsurface Defect Detection in Concrete Structures by Active Thermal Imaging. Sensors, 17(1718), doi--10.
• Farag, R., & Haldar, A. (2016). A Novel Concept for Reliability Evaluation Using Multiple Deterministic Analyses. INAE Letters, 1(3-4), 85--97.
• Farag, R., & Haldar, A. (2016). A novel reliability evaluation method for large engineering systems. Ain Shams Engineering Journal, 7(2), 613--625.
• Farag, R., Haldar, A., & El-Meligy, M. (2016). Reliability Analysis of Piles in Multilayer Soil in Mooring Dolphin Structures. Journal of Offshore Mechanics and Arctic Engineering, 138(5), 052001.
• Reyes-Salazar, A. .., Llanes-Tizoc, M. D., Bojorquez, J., Bojorquez, E., Lopez-Barraza, A. .., & Haldar, A. (2016). Force reduction factors for steel buildings with welded and post-tensioned connections. Bulletin of Earthquake Engineering, 14, 2827--2858.
• Al-Hussein, A. .., & Haldar, A. (2015). Health Assessment of Nonlinear Structural Systems. SRESA’s International Journal of Life Cycle Reliability and Safety Engineering, 4(1), 25--34.
• Al-Hussein, A. .., & Haldar, A. (2015). Structural Health Assessment at a Local Level Using Minimum Information. Engineering Structures, 88, 100--110.
• Al-Hussein, A. .., & Haldar, A. (2015). Structural Health Assessment using Extended and Unscented Kalman Filters. International Journal of Sustainable Materials and Structural Systems, 2(1/2), 52--76.
• Al-Hussein, A., & Haldar, A. (2015). A Novel Unscented Kalman Filter for Health Assessment of Large Structural Systems with Unknown Input. Journal of the Engineering Mechanics Division, ASCE, 141(7). doi:10.1061/(ASCE)EM.1943-7889.0000926
• Al-Hussein, A., & Haldar, A. (2015). Health Assessment of Nonlinear Structural Systems. International Journal of Life Cycle Reliability and Safety Engineering, Special Issue on Prognostics & Structuring Health Management, 4(1), 25--34.
• Al-Hussein, A., & Haldar, A. (2015). Health Assessment of Nonlinear Structural Systems. Journal of Life Cycle Reliability and Safety Engineering, Special Issue on Prognostics & Structuring Health Management, 4(1), 25-34.
• Al-Hussein, A., & Haldar, A. (2015). Unscented Kalman filter with unknown input and weighted global iteration for health assessment of large structural systems. Structural Control and Health Monitoring, DOI--10.
• Das, A. K., & Haldar, A. (2015). Issues on Structural Health Assessment and Monitoring under Measurement Uncertainty and Nonlinearity. International Journal of Life Cycle Reliability and Safety Engineering, Special Issue on Prognostics & Structuring Health Management, 4(2), 1--12.
• Das, A. K., & Haldar, A. (2015). Issues on Structural Health Assessment and Monitoring under Measurement Uncertainty and Nonlinearity. Journal of Life Cycle Reliability and Safety Engineering, Special Issue on Prognostics & Structuring Health Management, 4(2), 1-12.
• Haldar, A. (2015). Reliable Engineering Computations of Large Infrastructures. International Journal of Reliability and Safety, 9(2/3), 92--111.
• Le, T. S., Le, T. S., Huh, J., Huh, J., Ahn, J., Ahn, J., Haldar, A., & Haldar, A. (2015). Damage State Identification and Seismic Fragility Evaluation of the Underground Tunnels. Applied Mechanics and Materials, 775(doi:10.4028/www.scientific.net/AMM.775.2), 274--278.
• Reyes-Salazar, A. .., Haldar, A., Rivera-Salas, J. L., Boj'orquez-Mora, E., & L'opez-Barraza, A. (2015). Review of assumptions in Simplified Multi-Component and Codified seismic Response Evaluation Procedures. Structural Engineering, Korean Society of Civil Engineers, 19(5), 1320--1335.
• Reyes-Salazar, A., Haldar, A., Rivera-Salas, J. L., Bojórquez-Mora, E., & López-Barraza, A. (2015). Review of assumptions in Simplified Multi-Component and Codified seismic Response Evaluation Procedures. Korean Society of Civil Engineers, 19(5), 1320-1335. doi:DOI 10.1007/s12205-012-0190-z
• Al-Hussein, A., & Haldar, A. (2014). Structural Health Assessment at a Local Level Using Minimum Information. Engineering Structures.
• El-Bordany, R., El-Meligy, M., & Haldar, A. (2014). An Improved Reliability Analysis Method Mooring Dolphin Structures. Offshore Mechanics and Arctic Engineering, ASME, 136, 034501-1-034501-05.
• Peña, C., & Haldar, A. (2014). Three Dimensional Response Analysis of RC Bridges under Spatially Varying Seismic Excitation – Methodology. Journal of Structural Engineering, 41(3), 251-264.
• Peña, C., & Haldar, A. (2014). Three Dimensional Response Analysis of RC Bridges under Spatially Varying Seismic Excitation – Numerical Analysis and Observations. Journal of Structural Engineering, 41(3), 265-278.
• Reyes-Salazar, A., Bojorquez, E., Haldar, A., Lopez-Barraza, A., & Rivera-Salas, J. L. (2014). Ductility Reduction Factors for Steel Buildings Modeled as 2D and 3D Structures. Applied Mechanics and Materials, 595, 166-172.
• Reyes-Salazar, A., Bojórquez, E., Haldar, A., López-Barraza, A., & Rivera-Salas, J. L. (2014). Seismic Response of 3D Steel Buildings considering the Effect of PR Connections and Gravity Frames. The Scientific World Journal, 2014(Article ID 346156), 13 pages.
• Reyes-Salazar, A., Haldar, A., Rodelo-López, R. E., & Bojórquez, E. (2014). Effect of Damping and Yielding on the Seismic Response of 3D Steel Buildings with PMRF. The Scientific World Journal, 2014(Article ID 915494), 21.
• Haldar, A., Das, A. K., & Al-Hussein, A. (2013). Data Analysis Challenges in Structural Health Assessment using Measured Dynamic Responses. Advances in Adaptive Data Analysis, 5(4), 1350017-1 to 1350017-22.
• Chakraborty, S., Bhattacharjya, S., & Haldar, A. (2012). An Efficient Sensitivity Based Robust Optimization of Structures under Uncertainty,” International Journal of Numerical Methods and Engineering. International Journal of Numerical Methods and Engineering.
• Chakraborty, S., Bhattacharjya, S., & Haldar, A. (2012). Sensitivity importance-based robust optimization of structures with incomplete probabilistic information. International Journal for Numerical Methods in Engineering, 90(10), 1261-1277.
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  Abstract: Robust design optimization (RDO) is usually performed by minimizing the nominal value of a performance function and its dispersion considering equal importance to each individual gradient of the performance function. However, it is well known that all gradients are not equally important. An efficient sensitivity importance-based RDO technique is proposed in the present study for optimum design of structures characterized by bounded uncertain input parameters. The basic idea of the proposed RDO formulation is to improve the robustness of a performance function by using a new gradient index that utilizes the importance factors proportional to the importance of the gradients of the performance function. The same concept is also extended to the constraints. To enhance the robustness of the constraints, the constraint functions are also modified by using the importance factor proportional to the importance of the associated gradient of the constraint. Because all the variables are not equally important to capture the presence of uncertainty, an improved robust solution is obtained by the proposed approach compared with the conventional RDO approach. The present formulation is illustrated with the help of three informative examples. The results are compared with the conventional RDO results to study the effectiveness of the proposed RDO approach. © 2012 John Wiley & Sons, Ltd.
• Das, A. K., & Haldar, A. (2012). Health Assessment of Three Dimensional Large Structural Systems – A Novel Approach. International Journal of Life Cycle reliability and Safety Engineering, 1(1), 01-14.
• Das, A. K., Haldar, A., & Chakraborty, S. (2012). Health assessment of large two dimensional structures using limited information: Recent advances. Advances in Civil Engineering, 2012.
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  Abstract: Some recent advances of a recently developed structural health assessment procedure proposed by the research team at the University of Arizona, commonly known as generalized iterative least-squares extended Kalman filter with unknown input (GILS-EKF-UI) are presented. The procedure is a finite elements-based time-domain system-identification technique. It can assess structural health at the element level using only limited number of noise-contaminated responses. With the help of examples, it is demonstrated that the structure can be excited by multiple loadings simultaneously. The method can identify defects in various stages of degradation in single or multiple members and also relatively less severe defect. The defective element(s) need not be in the substructure, but the defect detection capability increases if the defect spot is close to the substructure. Two alternatives are suggested to locate defect spot more accurately within a defective element. The paper advances several areas of GILS-EKF-UI to assess health of large structural systems.
• Haldar, A. (2012). Effect of Uncertainty in the Frequency Content and Strong Motion Duration on the Structural Seismic Risks. International Journal of Ocean Engineering System, 2(1), 25-37.
• Haldar, A. (2012). Past, Present, and Future of Engineering under Uncertainty: Safety Assessment and Management. Journal of Life Cycle Reliability and Safety Engineering, 1(4), 39-52.
• Haldar, A., & Das, A. K. (2012). Health Assessment of Structures – Past, Present, and Future. International Journal of Life Cycle Reliability and Safety Engineering, 1(4), 53-63.
• Haldar, A., Farag, R., & Huh, J. (2012). A novel concept for the reliability evaluation of large systems. Advances in Structural Engineering, 15(11), 1879-1892.
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  Abstract: A general purpose novel reliability analysis method to estimate low probability of failure events for large complicated real nonlinear structures excited by dynamic loadings including seismic loading applied in time domain is presented. In this approach, only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the required reliability information. It is a significant improvement over other methods currently being developed in other disciplines. Several areas of response surface method are improved and advanced factorial design concepts are presented. The method is elaborated with the help of two informative examples. The proposed method found to be robust, efficient, and accurate. It can be used to estimate reliability of large complicated civil engineering systems.
• Das, A. K., & Haldar, A. (2011). Structural health assessment using only noise-contaminated responses. Vulnerability, Uncertainty, and Risk: Analysis, Modeling, and Management - Proceedings of the ICVRAM 2011 and ISUMA 2011 Conferences, 518-525.
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  Abstract: A novel nondestructive Structural Health Assessment (SHA) technique, known as the Generalized Iterative Least-Squares Extended Kalman Filter with Unknown Input (GILS-EKF-UI) method, is being developed at the University of Arizona. The procedure can detect defects in new, deteriorated or rehabilitated existing structures or just after large natural or manmade events. Most SI-based SHA approaches use excitation and response information to identify a structure. Excitation information is not available in most cases. It could be noise-contaminated and the SI concept may not be applicable. For large complicated real structures, it may not be possible to measure responses at all dynamic degrees of freedom and they always contain noise. Addressing all the issues, the GILS-EKF-UI method is being developed and is presented here. Copyright © ASCE 2011.
• Farag, R., El-Meligy, M., & Haldar, A. (2011). Reliability analysis of mooring dolphin structures. Vulnerability, Uncertainty, and Risk: Analysis, Modeling, and Management - Proceedings of the ICVRAM 2011 and ISUMA 2011 Conferences, 914-921.
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  Abstract: A mooring dolphin structures (MDS), consisting of steel-pipe-piles and soil around them, are important elements of marine structures. The reliability analysis of such complicated systems is very challenging. The limit state functions for them are implicit in nature. Reliability evaluation using the classical Monte Carlo simulation technique may not be practical since each deterministic evaluation will require several hours of computer time. A new hybrid method is presented in this paper. The system is represented by finite elements and its reliability is estimated by intelligently integrating the stochastic finite element, response surface methods, and advanced factorial schemes. The procedure is verified with the help of an example. Copyright © ASCE 2011.
• Huh, J., & Haldar, A. (2011). A novel risk assessment for complex structural systems. IEEE Transactions on Reliability, 60(1), 210-218.
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  Abstract: Risk management is an essential tool for safe, economical, and efficient design, operation, and maintenance of complex engineering systems. Seismic risk assessment of structures, particularly in nuclear power plants, needs special attention from the reliability community. Available risk assessment methods may not be sufficient to estimate the risk of complex systems made with different materials, numerous ways elements are connected to each other, and excited by dynamic loadings including seismic loading applied in the time domain. A hybrid risk assessment approach is proposed by intelligently integrating the stochastic finite element method, and the response surface method. It is capable of estimating the probability just before failure considering all major sources of nonlinearity and uncertainty, eliminating the deficiencies of the currently available reliability methods. With the help of the illustrative examples, it is shown that the method is robust, accurate, and efficient in estimating risk of complex systems excited by dynamic loadings applied in the time domain. © 2010 IEEE.
• Das, A. K., & Haldar, A. (2010). Structural integrity assessment under uncertainty for three dimensional offshore structures. International Journal of Terraspace Science and Engineering, 2(2), 101-111.
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  Abstract: A novel structural integrity assessment technique using uncertain response information is under development by the research team at the University of Arizona. The team successfully verified the method for two dimensional truss and frame structures. The team is now in the process of extending the method for three dimensional (3D) truss type structures. The essential feature of the procedure is that it is a finite element based linear system identification technique which can accurately identify a structure without causing any disruption to the normal operating condition. Using only the noise contaminated response information, the procedure is capable of identifying defect at the element level of a structure by tracking changes in the stiffness parameters of the elements. The information on the dynamic excitation is not necessary. The procedure identifies the dynamic loading as a by-product. It is referred in this paper as the 3D Modified Iterative Least Squares with Unknown Input (3D-MILS-UI). The procedure and its verification are presented in this paper. The procedure is verified assessing structural integrity of a 3-D truss type offshore tower. The tower is subjected to one or multiple sinusoidal loadings and impact loadings; types of loadings expected during the operation of the tower. Three types of damage scenarios of the tower are considered - multiple broken members, multiple damaged elements in terms of the reduction in the cross sectional areas and a combination of broken members and damaged elements. Both noise-free and noise-contaminated responses are considered for the defect identification purpose. The results indicate that the 3D-MILS-UI procedure can accurately assess structural integrity by locating the defective elements and quantifying the severity of defects in them.
• Haldar, A., & Das, A. K. (2010). Prognosis of structural health: Non-destructive methods. International Journal of Performability Engineering, 6(5), 487-498.
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  Abstract: For the prognosis of structural health, non-destructive defect assessment procedures are under active development by the profession. Two such procedures now under development by the research team at the University of Arizona, are MILS-UI and GILS-EKF-UI. They indicate a considerable application potential. The unique feature of the algorithms is that they can identify members' properties and in the process access the health of a structural system using only dynamic responses completely ignoring the excitation information. Although mathematically elegant, their practical implemental potential to identify defect-free and defective (single or multiple defects) states need critical evaluation and is discussed in the paper. With the help of an illustrative example, it was shown that both the MILS-UI and GILS-EKF-UI methods can identify defect-free and defective states of a structure very well. Both methods successfully indentified the presence of multiple defects. Ignoring responses at vertical dynamic degrees of freedoms did not alter the outcomes ofthe nondestructive evaluation for the problem under consideration. Both methods also correctly identified less severe defect in terms of loss of area over a finite length. It can be concluded that the methods are capable of identifying small and large defects. © RAMS Consultants.
• Haldar, A., & Farag, R. (2010). A novel reliability evaluation method for large dynamic engineering systems. 2010 2nd International Conference on Reliability, Safety and Hazard, ICRESH-2010: Risk-Based Technology and Physics-of-Failure Methods, 21-31.
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  Abstract: A novel reliability evaluation method for large nonlinear engineering systems excited by dynamic loading applied in time domain is presented. For this class of problems, the performance functions are expected to be function of time and implicit in nature. Available first- or second-order reliability method (FORM/SORM) will be challenging to estimate reliability of such systems. Because of its inefficiency, the classical Monte Carlo simulation (MCS) method also cannot be used for large nonlinear dynamic systems. In the proposed approach, using only tens instead of hundreds or thousands of deterministic evaluations at intelligently selected points are used to extract the reliability information. A hybrid approach, consisting of the stochastic finite element method (SFEM) developed by the author and his research team using FORM, response surface method (RSM), an interpolation scheme, and advanced factorial schemes is proposed. The method is clarified with the help of several numerical examples. It provides an alternative to the classical random vibration approach. It is also an alternative when the basic MCS becomes very inefficient. © 2010 IEEE.
• Huh, J., Haldar, A., Kwak, K., & Park, J. (2010). Realistic risk assessment of axially loaded pile-soil system using a hybrid reliability method. Georisk, 4(3), 118-126.
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  Abstract: The behaviour of an axially loaded pile embedded in a non-homogeneous soil deposit considering the pile-soil nonlinear interaction effect is realistically evaluated, and a new efficient and accurate hybrid reliability method is proposed for estimating the corresponding risk. The complicated problem is first deterministically formulated and then the uncertainties associated with the various design variables are considered explicitly. The hybrid reliability approach intelligently integrates the concepts of the response surface method, the finite difference method, the first-order reliability method, and an iterative linear interpolation scheme. The soil around the pile is represented by a series of springs. The systemis expected to represent a realistic and efficient load-transfer mechanism. The soil-pile dual system is then deterministically analysed using the finite difference method. Uncertainties associated with load conditions, material and sectional properties of the pile and non-homogeneous soil properties are then incorporated in to the deterministic formulation resulting in the hybrid reliability approach. The risks corresponding to both serviceability and strength limit states are estimated. With the help of an illustrative example, the applicability, accuracy and efficiency of the proposed algorithm in the safety assessment of axially loaded pile-soil systems are demonstrated. The reliability evaluation procedure is verified using the Monte Carlo simulation technique. © 2010 Taylor & Francis.
• El-Bordany, R., El-Meligy, M., & Haldar, A. (2009). Reliability of mooring dolphin structures: An insight into partial safety factors. Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering: The Academia and Practice of Geotechnical Engineering, 2, 1293-1296.
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  Abstract: The steel-pile-soil-system as a mooring dolphin structure is an important element of marine structures. However, the reliability of this system is very difficult to predict due to inherent uncertainties in the marine environment. The objective of this paper is twofold; (i) to investigate the influences of several sources of uncertainties on different limit states of a steel-pile-soil mooring dolphin under axial and lateral loading conditions and (ii) to suggest partial safety factors required for the codified design. In doing so, the response surface method, RSM is used in reliability analysis. A grid of sampling response points is obtained from a realistic built up NLFEM. Then, this grid is used to formulate a response function equivalent to the implicit limit state function With the help of realistic examples, the most important random variables and limit state are identified. For routine design, partial safety factors are proposed. © 2009 IOS Press.
• Haldar, A. (2009). Is the inverse problem technique appropriate for structural health assessment?. Current Science, 97(8), 1187-1195.
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  Abstract: Structural health assessment techniques using system identification-based approaches have recently generated a considerable amount of multidisciplinary research interest. However, in 1979, it was stated that the inverse transformation technique could not identify a system with measured response information. Presence of many sources of error including noise, high frequency content, slope, DC bias, etc. in the measured response information were considered to be the major reasons. However, removing these sources from the measured responses may not be adequate to eliminate the non-convergence problem. In this article, it is conclusively demonstrated that a system can be identified if the amplitude and phase shift errors embedded in the measured responses are mitigated properly. The noise may not be the primary reason for the non-convergence. The conclusions made here are primarily based on the analytical and experimental works completed by the author and his team. Their experience indicates that the system identificationbased structural health assessment techniques have unlimited application potential.
• Mehrabian, A., Ali, T., & Haldar, A. (2009). Nonlinear analysis of a steel frame. Nonlinear Analysis, Theory, Methods and Applications, 71(12), e616-e623.
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  Abstract: Nonlinear seismic analysis is used in structural engineering profession to design steel frames for moderate to strong earthquakes. Following the Northridge earthquake of 1994 in Southern California, widespread damage to many steel frames was discovered. As a result of multi-million dollar efforts by the professionals, many post-Northridge steel beam-column connection designs were proposed. They are essentially partially-restrained (PR) connections, and their presence adds yet another major source of nonlinearity that must be considered appropriately in nonlinear seismic response analysis. In this paper, a case study of analytical investigation of nonlinear seismic performance of a 9-story steel frame is presented. We consider major sources of nonlinearity in the system including the nonlinear behavior of the connections. Using the four-parameter Richard model, a mathematical model is proposed first to represent moment-relative rotation (M - θ) curves for a proprietary steel connection. The model can generate (M - θ) curves for other beam-column assemblies. Time-domain, nonlinear seismic response of a steel moment-resisting frame (SMRF) in the presence of this type of connection and pre-Northridge bolted-web, welded-flange (denoted here as BWWF) connections are evaluated. The results are then compared with fully-restrained (FR) steel connections typically used in the design. The results analytically confirmed the beneficial effects of connections observed in full-scale testing. © 2008 Elsevier Ltd. All rights reserved.
• Reyes-Salazar, A., Bojórquez, E., López-Barraza, A., Leon-Escobedo, D. D., & Haldar, A. (2009). Some issues regarding the structural idealization of perimeter moment-resisting steel frames. ISET Journal of Earthquake Technology, 46(3-4), 133-146.
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  Abstract: To improve economy and increase efficiency in designing the steel buildings made with W-shape members, the use of two-dimensional moment-resisting steel frames (MRSFs) in the perimeter, to carry seismic loads, and of interior gravity frames (IGFs), to carry gravity loads, has become very popular. This provides a simpler frame to analyze and design. The behavior of such buildings is addressed in this paper. Two model buildings suggested by FEMA are used in the study. Linear and nonlinear global and local responses are calculated. The results indicate that modelling 3-D structures with 2-D perimeter frames is conservative and that ignoring the lateral load carrying capacity of IGFs or ignoring the rigidity of connections in those adds several levels of conservatism in the overall design. This study also indicates that IGFs may need to carry up to 35% of the total lateral load caused by the seismic excitation. An implication of this is that the members in IGFs may not be able to carry this unexpected load.
• Haldar, A., & Martinez-Flores, R. (2008). A novel methodology for health assessment of existing steel structures. Journal of Structural Engineering (Madras), 35(1), 82-91.
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  Abstract: A novel methodology is presented for health assessment of existing steel structures after natural and manmade hazards or due to natural aging process. The analytical concept and its desirable features are briefly discussed first. Then, the method is extensively verified using computer generated analytical response information and the response information obtained in laboratory investigations on defect-free and defective beams and a three-story one-bay steel frame. Two cracks were cut in the beam. Several defects were introduced in the frame in terms of removing a member, reducing the cross sectional area over a finite length, introducing several cracks and a single crack, presence of different defects at different locations, etc. The capability of the method was studied to check if it could identify the defects and their locations. The research team called the method as the GDLS-EKF-UI method. It is essentially a finite element-based system identification technique. It can identify defects at the local element level using only limited noise-contaminated response information and without using any information on excitation. The method is conclusively verified. It is recommended that the method be used to assess health of existing steel structures.
• Haldar, A., & Mehrabian, A. (2008). Structural engineering in the new millennium: Opportunities and challenges. Structural Survey, 26(4), 279-301.
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  Abstract: Purpose - Structural engineering as a part of civil engineering has over 5,000 years of distinguished history, as documented in this paper. An attempt is made in this paper to define structural engineering as it exists at present, then some historical structures are identified. Design/methodology/approach - The advances of structural engineering are discussed in chronological order, encompassing the development of the concept, analysis, the use of innovative construction materials, and construction. The developments which necessitated the change of design philosophies are presented, and the current status of structural engineering is discussed in terms of several specific topics. Opportunities and challenges in the new millennium in structural engineering are then presented in terms of education, service to society, and research. Findings - In the past, structural engineering always met the challenges it faced. It helped to improve our quality of life, and its role in society is not expected to change in the near future. Originality/value - The paper has provided an over-view of this important profession - from ancient history to the present day. Based on research over several decades it offers a prediction of the direction in which this profession and the academic research that underpins it is likely to take in the future.
• Haldar, A., Martinez-Flores, R., & Katkhuda, H. (2008). Crack detection in existing structures using noise-contaminated dynamic responses. Theoretical and Applied Fracture Mechanics, 50(1), 74-80.
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  Abstract: Crack detection is existing structures using measured dynamic response information is presented in this paper. The general area of health assessment of existing structures in the presence of uncertainty in modeling the structure, characteristics of sensors, and the dynamic response information collected by the sensors is emphasized. A time domain system identification-based procedure is proposed to assess health of a structure at the finite element level in the presence of all major sources of uncertainty. It is denoted as the GILS-EKF-UI method. The method does not require information on excitation that caused the response and the noise-contaminated response information needs not be available at all dynamic degrees of freedom. The method is verified using computer generated analytical and actual measured response information emphasizing three items: (1) identification of the defect-free frame, (2) detection of location of a crack accurately within a defective element, and (3) detection of a crack using limited response information using the GILS-EKF-UI method. © 2008.
• Haldar, A., Martinez-Flores, R., & Katkhuda, H. (2008). Issues in Kalman filter-based damage evaluation without excitation information. Proceedings of the World Forum on Smart Materials and Smart Structures Technology, SMSST'07, 79-.
• Huh, J., Haldar, A., Kwak, K., & Park, J. (2008). Probabilistic reliability estimation of an axially loaded pile. 12th International Conference on Computer Methods and Advances in Geomechanics 2008, 3, 1811-1817.
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  Abstract: A new efficient and accurate hybrid reliability method is proposed to estimate risk of an axially loaded single pile considering pile-soil interaction effect. Uncertainties associated with all the design variables are considered appropriately. It intelligently integrates the concepts of the response surface method, the finite difference method, the first-order reliability method, and an iterative linear interpolation scheme. The soil around the pile is represented by a series of springs. The system represents a realistic and efficient load-transfer mechanism. The dual system is then deterministically analysed using the finite difference method. Uncertainties associated with load conditions, material and sectional properties of the pile and soil properties are explicitly considered. The risks corresponding to both serviceability and strength limit states are estimated. With help of realistic examples, the applicability, accuracy and efficiency of the proposed algorithm in the safety assessment of axially loaded pile-soil system are demonstrated. The procedure is also verified using the Monte Carlo simulation technique.
• Katkhuda, K., & Haldar, A. (2008). A novel health assessment technique with minimum information. Structural Control and Health Monitoring, 15(6), 821-838.
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  Abstract: A novel structural health assessment method is proposed for detecting defects at the element level using only minimum measured response information considering imperfect mathematical model representing the structure, various sources of uncertainty in the mathematical model, and uncertainty in the measured response information. It is a linear time domain finite element-based system identification procedure capable of detecting defects at the local element level using only limited response measurements and without using any information on the exciting dynamic forces. The technique is a combination of the modified iterative least-squares technique with unknown input excitation (MILS-UI) proposed earlier by the research team at the University of Arizona and the extended Kalman filter with a weighted global iteration (EKF-WGI) procedures to address different sources of uncertainty in the problem. The authors denote the new method as GILS-EKF-UI. To implement the concept, a two-stage substructure approach is used. In the first stage, a substructure is selected that satisfies all the requirements for the MILS-UI procedure. This provides information on the initial state vector and the input excitation required to implement any EKF-based procedure. In the second stage, the EKF-WGI is applied to identify the whole structure. This way the whole structure, defect free or defective, can be identified with limited response measurements in the presence of uncertainty and without using excitation information. The theoretical concept behind this novel method is presented in this paper. Copyright © 2007 John Wiley & Sons, Ltd.
• Martinez-Flores, R., Katkhuda, H., & Haldar, A. (2008). Structural performance assessment with minimum uncertainty-filled information. International Journal of Performability Engineering, 4(2), 121-140.
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  Abstract: A novel structural performance/health assessment method, denoted as GILS-EKF-UI, is under development by the research team at the University of Arizona. The procedure is essentially inverse solution of a system identification-based algorithm in the presence of uncertainty. The unique feature of the algorithm is that it can identify members' properties and in the process access the performance/health of a structural system using only noise-contaminated dynamic response information measured at few locations completely ignoring the excitation information. The experimental and analytical verification of the method is emphasized in this paper. To verify the GILS-EKF-UI method using minimum response information, a substructure is considered. A two-dimensional defect-free steel frame is identified using limited analytical (noise-free and noise-contaminated) and experimental responses. Several defects were then introduced in the frame. Two defects in particular; by removing a member and by reducing the cross sectional area of a member over a finite length, are presented in the paper. In all cases, the GILS-EKF-UI method predicted the health of the frame by correctly identifying the defect and its location, conclusively establishing the viability of the novel concept.
• Reyes-Salazar, A., Lopez-Barraza, A., Lopez-Lopez, A., & Haldar, A. (2008). Multi-component seismic response analysis - A critical review. Journal of Earthquake Engineering, 12(5), 779-799.
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  Abstract: Issues related to multi-components seismic response analysis are critically reviewed and their implications with respect to the current codified approaches are studied. The issues specifically addressed are: (1) the directions of earthquake forces to excite a structure when the direction of the potential epicenter is known; (2) different commonly used combination rules to obtain the critical response when responses are available in different directions; and (3) the applicability of the combination rules for elastic and inelastic analyses. Based on an extensive parametric study consisting of three-dimensional 1-, 3-, 8-, and 15- story buildings made of moment-resisting steel frames and 20 recorded earthquakes, it is observed that the principal components produce larger responses than the normal components. The 30% and SSRS rules generally underestimate the axial loads in columns. The 30% combination rule is slightly better than the SSRS rule. For both rules, the uncertainty in the estimation of the axial loads in terms of COV is very large (about 25%). The statistics obtained for axial loads and total base shear indicate that the combination rules are applicable for both elastic and inelastic cases. The critical response could be obtained for an orientation different from that of the principal components. The differences are found to be slightly greater for the scaled earthquakes producing a considerable inelastic behavior. Considering the enormous amount of efforts needed to address the directionality effect, it is believed that the responses obtained by the principal components will be acceptable in most cases; however, for critical structures the components should be rotated to obtain the critical responses.
• Vo, P. H., & Haldar, A. (2008). Health assessment of beams - Theoretical formulation and analytical verification. Structure and Infrastructure Engineering, 4(1), 33-44.
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  Abstract: Theoretical aspects and analytical verification of a novel non-destructive structural health assessment procedure being developed by a research team at the University of Arizona are presented in this paper. The experimental verification of the procedure is discussed in the companion paper. The health assessments of fixed ended and simply supported beams are specifically addressed. The basic procedure is a finite element-based linear time domain system identification technique where input excitation information is not required. Beams are represented by finite elements. By tracking the changes in the moduli of rigidities of the elements, the current health of the beams can be assessed. Rayleigh damping is used in the dynamic formulation to reduce the size of the identification problem. How to establish the optimal number of finite elements is first discussed. Defects, in terms of two notches, are introduced in an element in fixed ended and simply supported beams. Analytical responses of defect-free and defective beams excited by sinusoidal loadings are evaluated by using a computer programme. Using analytical response information only and completely ignoring the input excitation information, the health of the beams is successfully predicted in all cases. When defects were present, the method also identified the location of the defective element. The beams were then experimentally tested to verify conclusively the proposed method, as discussed in the companion paper.
• Vo, P. H., & Haldar, A. (2008). Health assessment of beams-experimental verification. Structure and Infrastructure Engineering, 4(1), 45-56.
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  Abstract: A novel nondestructive structural health assessment procedure now under development at the University of Arizona and presented in a companion paper, is experimentally verified. The experimental verifications of the procedure to identify defect-free and defective fixed ended and simply supported beams are presented in this paper. In this approach, acceleration and rotational time histories are measured at pre-selected node points. They are then post-processed to remove several sources of error including noise, high frequency content, slope, and DC bias. The post-processed response information is then successively integrated to obtain the corresponding velocity and displacement time histories. Even when these sources of error were removed from the response information, the proposed method failed to identify the beams. Several factors including noise, data latency, scale factor and cross coupling error were investigated. Amplitude and phase errors in the accelerometer's measurements were found to be the root cause. Alternative approaches are proposed to mitigate them. Following the suggested procedures, defect-free and defective fixed ended and simply supported beams are correctly identified. The proposed NDE procedure is accurate and robust, and can identify defects at the local element level in the context of the finite element representation. The laboratory experiments clearly and conclusively verified the proposed algorithm, i.e. a beam can be identified without using input excitation information and using only noise-contaminated response information and established its application potential.
• Haldar, A., Martinez-Flores, R., & Katkhuda, H. (2007). Verifications of a novel structural health assessment technique. Applications of Statistics and Probability in Civil Engineering - Proceedings of the 10th International Conference on Applications of Statistics and Probability, ICASP10, 513-514.
• Huh, J., & Haldar, A. (2007). Seismic reliability of frame structures emphasizing uncertainty in the frequency content. Applications of Statistics and Probability in Civil Engineering - Proceedings of the 10th International Conference on Applications of Statistics and Probability, ICASP10, 125-126.
• Martinez-Flores, R., & Haldar, A. (2007). Experimental verification of a structural health assessment method without excitation information. Journal of Structural Engineering (Madras), 34(1), 33-39.
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  Abstract: A nondestructive technique to assess structural health after natural and man-made hazards under development at the University of Arizona is experimentally verified. The procedure is essentially a linear time-domain system identification technique. A structure is represented by finite elements. The procedure tracks changes in the stiffness property of all the elements in a structure. Since the input excitation information is not available in most cases, the proposed technique identifies a structure and thus assesses its health in the absence of such information. Experimental verification is emphasized in this paper. A two-dimensional three-story one-bay steel frame was built in the laboratory. The defect-free frame was identified using computer generated and laboratory measured response information. Several defects with various amount of severity were introduced. Two less severe defects, (i) reducing the cross sectional area over a finite length and (ii) presence of a crack, are specifically addressed in the paper. The frame was represented by three sets of finite element and the location of defect with respect to a node is then studied. The results indicate that the accuracy of the proposed method is much better than the other currently available methods even when the input excitation information was used for identification purposes. The defect identification process improves if a node is selected close to the defect spot. It is established, using both theoretical and laboratory investigations, that the proposed method can be used for structural health assessment after natural and man-made hazards.
• Mehrabian, A., & Haldar, A. (2007). Mathematical modelling of a "post-Northridge" steel connection. International Journal of Modelling, Identification and Control, 2(3), 195-207.
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  Abstract: A robust mathematical model to capture the behaviour of an attractive "post-Northridge" type, Partially Restrained (PR) steel connection is proposed. The proposed procedure captures the loading behaviour for this type of connection reasonably well. It is suggested that the unloading and reloading parts of M - θ curves required for seismic analysis can be theoretically generated by using the Masing Rule. This study confirms some of the important desirable features of the connection. Although it is a PR connection, its initial stiffness is similar to that of bolted, a single web angle with top and seat connection, generally considered to be a Fully Restrained (FR) connection. Thus, a steel frame with the connection studied is not expected to show weakness in satisfying serviceability requirements. Furthermore, the beam develops full plastic moment and the ductility of the connection and its seismic energy dissipation characteristics are expected to be significantly improved. Copyright © 2007 Inderscience Enterprises Ltd.
• Haldar, A. (2006). American Society of Mechanical Engineers, Safety Engineering and Risk Analysis Division, SERA. American Society of Mechanical Engineers, Safety Engineering and Risk Analysis Division, SERA.
• Haldar, A., Huh, J., & Mehrabian, A. (2006). Reliability evaluation using finite element method. American Society of Mechanical Engineers, Safety Engineering and Risk Analysis Division, SERA.
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  Abstract: A robust and sophisticated structural reliability evaluation procedure is presented. Reliability of any structural systems represented by finite elements can be evaluated using the algorithm. The authors called it a stochastic finite element method. Despite the significant recent progress in the risk and reliability analysis techniques, a large segment of the engineering profession is not familiar with them and thus fails to use them in everyday practices. The procedure is expected to fill that vacuum. Many sources of nonlinearity generally overlooked in the profession can be incorporated in the algorithm. Uncertainties in the load and resistance-related variables are modeled as realistically as possible. The estimation of the failure probability implies that structural behavior just before failure needs to be captured as accurately as possible. The algorithm is capable of evaluating the probability of failure addressing all the related issues. With the help of four informative examples, the application potential of the procedure is clearly demonstrated. It is similar to the deterministic methods and is not expected to be complicated to the practicing engineers; thus, promoting its wider applications. It is shown that the observations made in laboratory experiments can be explained with the procedure. It is hoped that the method will be used in the future to estimate the reliability of real structures. Copyright © 2006 by ASME.
• Haldar, A., Huh, J., & Mehrabian, A. (2006). Time-domain seismic reliability of nonlinear structures. Sadhana - Academy Proceedings in Engineering Sciences, 31(4), 359-382.
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  Abstract: A novel reliability analysis technique is presented to estimate the reliability of real structural systems. Its unique feature is that the dynamic loadings can be applied in time domain. It is a nonlinear stochastic finite element logarithm combined with the response surface method (RSM). It generates the response surface around the most probable failure point and incorporates information of the distribution of the random variables in the RSM formulation. It is verified using the Monte Carlo simulation technique, and is found to be very efficient and accurate. Most sources of nonlinearlity and uncertainty can be explicitly incorporated in the formulation. The flexibility of connections, represented by moment-relative rotation (M-θ) curves, is addressed. After the Northridge earthquake of 1994, several improved steel connections were proposed. Structural Sesimic Design Associates (SSDA) tested several full-scale proprietory slotted web beam-column connections. The authors suggested (M-θ) curves for this connection using actual test data. Behaviours of steel frames, assuming the connections are fully restrained, partially restrained, consisting of pre- and post-Northridge connections are evaluated and compared. Desirable features of the post-Northridge connections observed during testing are analytically confirmed. Laterally weak steel frame is then strengthened with concrete shear walls. Capabilities and the advanced nature of the method are demonstrated with the help of realistic examples.
• Katkhuda, H., & Haldar, A. (2006). Defect identification under uncertain blast loading. Optimization and Engineering, 7(3), 277-296.
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  Abstract: A novel finite element-based system identification procedure is proposed to detect defects in existing frame structures when excited by blast loadings. The procedure is a linear time-domain system identification technique where the structure is represented by finite elements and the input excitation is not required to identify the structure. It identifies stiffness parameter (EI/L) of all the elements and tracks the changes in them to locate the defect spots. The similar procedure can also be used to monitor health of structures just after natural events like strong earthquakes and high winds. With the help of several numerical examples, it is shown that the algorithm can identify defect-free and defective structures even in the presence of noise in the output response information. The accuracy of the method is much better than other methods currently available even when input excitation information was used for identification purpose. The method not only detects defective elements but also locate the defect spot more accurately within the defective element. The structures can be excited by single or multiple blast loadings and the defect can be relatively small and large. With the help of several examples, it is established that the proposed method can be used as a nondestructive defect evaluation procedure for the health assessment of existing structures. © Springer Science + Business Media, LLC 2006.
• Martinez-Flores, R., Haldar, A., & Katkhuda, H. (2006). Structural health assessment after an impact. American Society of Mechanical Engineers, Safety Engineering and Risk Analysis Division, SERA.
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  Abstract: An innovative technique to assess structural health just after subjected to impulsive loadings (blasts, explosions, etc.) underdevelopment at the University of Arizona was experimentally verified and is presented in this paper. The authors called it the Generalized Iterative Least Square Extended Kalman Filter with Unknown Input (GILS-EKF-UI) method. The system is represented by finite elements and a Kalman filter-based system identification (SI) technique is used to identify the system. Some of the major characteristics of the method are that it does not require information on input excitation and can identify a system with limited noise-contaminated response information measured at few node points. To implement the Kalman-filter based algorithm, the information on the input excitation and the initial state vector must be available. The authors proposed a two-stage approach. In the first stage, based on the limited measured response information available at the locations of the sensors, a substructure is identified. After the completion of the first stage, the input excitation information that caused the responses and the stiffness of all the elements in the substructure can be evaluated. Then, in stage 2, the Kalman-filter based algorithm is used to identify the whole structure. The experimental verification of the method is emphasized in this paper. Copyright © 2006 by ASME.
• Haldar, A., & Huh, J. (2005). Reliability evaluation of dynamic systems in time domain using nonlinear finite element method. 3rd M.I.T. Conference on Computational Fluid and Solid Mechanics, 247-249.
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  Abstract: Reliability analysis of nonlinear structures in the presence of major sources of nonlinearity is becoming an integral part of performance-based design guidelines. Finite element method is routinely used for the realistic representation of nonlinear structural behavior. However, the use of nonlinear finite element method will make the performance or limit state function, generally required for the reliability analysis, to be implicit. The authors propose a reliability evaluation technique when the limit state function is implicit. In this paper, the concept is extended to dynamic problems. The unique feature of this approach is that the uncertain dynamic loadings, including seismic loading, can be applied in time domain for the reliability evaluation. © 2005 Elsevier Ltd.
• Katkhuda, M., Martinez, R., & Haldar, A. (2005). Health assessment at local level with unknown input excitation. Journal of Structural Engineering, 131(6), 956-965.
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  Abstract: A finite-element-based procedure is proposed to identify defects in existing structures and evaluate their extent at the local element level for the purpose of health assessment. The procedure is a time-domain system identification technique where input excitation is not required to identify a structure. It estimates the dynamic properties of a structure in terms of stiffness and damping at the element level in a finite-element representation. The method can be used to precisely locate a defective spot in an element. Although input excitation information is not required, examples are used to show that the algorithm is robust enough to identify a structure excited by different types of loading. Structures can be excited simultaneously by multiple loadings, and the response information can be noise-free or noise-contaminated. Defects can be small or relatively large. In all cases, the algorithm identified the structures correctly. The error in the identification is considerably smaller than that of other available methods where input excitation information is used to identify a structure. With the help of examples, it is shown that the algorithm can potentially be used as a nondestructive evaluation technique for health assessment of existing structures with minimum disruption of operations. Since the procedure is very simple and requires only a few seconds of response information, it is expected to be very economical and efficient. © ASCE.
• Mehrabian, A., & Haldar, A. (2005). Some lessons learned from post-earthquake damage survey of structures in Bam, Iran earthquake of 2003. Structural Survey, 23(3), 180-192.
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  Abstract: Purpose - Some lessons learned from post-earthquake damage survey of structures affected by the Bam earthquake of December 26, 2003 in Iran are encapsulated in this paper. The Bam earthquake caused catastrophic structural damage in the region. Design/methodology/approach - A method similar to that of rapid evaluation procedure (REP), recommended by the Applied Technology Council (ATC-20) in the USA, was used for damage survey. Findings - Bam represents a typical ancient city in many countries around the world. Most of the structures in the region are made of adobe, unreinforced masonry, steel and unreinforced/reinforced concrete. Some of the main types of structural damage, their causes, and potential remedial measures are characterized with an emphasis on the very basic fundamental principles of earthquake-resistant design. Practical implications - The research reported has considerable implications for other seismic-affected regions of the world. Originality/value - A first hand-account of the catastrophic damage caused by this natural disaster and the implications for future design and construction in seismic-affected areas. © Emerald Group Publishing Limited.
• Mehrabian, A., Haldar, A., & Reyes-Salazar, A. (2005). Seismic response analysis of steel frames with post-North ridge connection. Steel and Composite Structures, 5(4), 271-287.
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  Abstract: The seismic behavior of two steel moment-resisting frames, which satisfy all the current seismic design requirements, are evaluated and compared in the presence of pre-Northridge connections denoted as BWWF and an improved post-Northridge connections denoted as BWWF-AD. Pre-Northridge connections are modeled first as fully restrained (FR) type. Then they are considered to be partially restrained (PR) to model their behavior more realistically. The improved post-Northridge connections are modeled as PR type, as proposed by the authors. A sophisticated nonlinear time-domain finite element program developed by the authors is used for the response evaluation of the frames in terms of the overall rotation of the connections and the maximum drift. The frames are excited by ten recorded earthquake time histories. These time histories are then scaled up to produce some relevant response characteristics. The behaviors of the frames are studied comprehensively with the help of 120 analyses. Following important observations are made. The frames produced essentially similar rotation and drift for the connections modeled as FR type and PR type represented by BWWF-AD indicating that the presence of slots in the web of beams in BWWF-AD is not detrimental to the overall response behavior. When the lateral displacements of the frames are significantly large, the responses are improved if BWWF-AD type connections are used in the frames. This study analytically confirms many desirable features of BWWF-AD connections. PR frames have longer periods of vibration in comparison to FR frames and may attract lower inertia forces. However, calculated periods of the frames of this study using FEMA 350 empirical equation is longer than those calculated using dynamic characteristics of the frames. This may result in even lower design forces and may adversely influence the design.
• Chen, G., & Haldar, A. (2004). Fatigue reliability assessment and updating with on-line nondestructive inspection for pressure vessels. American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 487, 41-48.
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  Abstract: Fatigue reliability assessment of pressure vessels is an important challenge to the engineering profession. The challenge is present during the whole life of pressure vessels. The problem is comprehensively studied and is reported in this paper. A fatigue reliability assessment technique is presented first. Nondestructive Inspections are routinely used to maintain the reliability to an acceptable level during the lifetime of a pressure vessel. At present, information from the nondestructive inspections (NDIs) is rarely used for safety evaluation. Even if no crack is detected during an inspection, it provides valuable information that is often overlooked. A reliability updating method is presented to address this weakness in the fatigue reliability evaluation of pressure vessels. The basic reliability method is extended to estimate the updated reliability. Nondestructive inspections are generally conducted at a specified time interval. To facilitate the continuous fatigue reliability evaluation, an on-line intelligent NDI technology is incorporated. The methodology is explained with the aid of an example. It is expected that the fatigue reliability evaluation of pressure vessels will be significantly improved if the proposed method is used.
• Haldar, A., Feng, M. Q., & Aktan, A. E. (2004). Issues on performance-based engineering for buildings and bridges. Proceedings of the 2004 Structures Congress - Building on the Past: Securing the Future, 11-18.
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  Abstract: Structures including buildings and bridges deteriorate and may not function in a satisfactory way as expected with time. Increasing number of cases of lack of satisfactory performances prompted the profession to consider developing performance-based design guidelines replacing or at least providing alternatives to the current specification (code) based practices. However, before developing such guidelines, the civil engineering profession should reach consensus on the definition of performance and establish quantitative, measurable indices that will permit the measurement of current or the projection of expected future performances. Performance-based design concept depends on many inter-connected issues including areas of applications, definition of performance, tools for measuring performance, quantitative indices that need to be satisfied, and performance under uncertainty. It is also important to note that since all major building codes on concrete, steel, wood, and masonry are now based on the Load and Resistance Factor Design (LRFD) concept; the future performance-based design guidelines should reflect the thinking behind this same concept. It is also known that the performance-based design concept is relatively new for civil engineers, the area is evolving, and comprehensive basic research is in its infancy. The paper will outline some of the recent thoughts on developing performance-based design guidelines.
• Katkhuda, H., Flores, R. M., & Haldar, A. (2004). A novel defect identification and structural health assessment technique. Journal of Structural Engineering (Madras), 31(1), 1-8.
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  Abstract: A novel non-destructive defect identification and structural health assessment procedure is presented in this paper. It can detect defects at the local element level of large structures under normal operating conditions or just after a major natural disaster. The procedure is essentially a linear time-domain system identification technique. A structure is represented by finite elements. The procedure tracks changes in the stiffness properties of all the elements in a structure. Since the input excitation information is not available in most cases, the proposed nondestructive evaluation (NDE) algorithm identifies a structure in the absence of such information. Noise in the response information cannot be avoided, and the proposed approach is capable of identifying a structure with noise-laden output response information. With the help of examples, it is shown that the algorithm can identify defect-free and defective structures very accurately even in the presence of noise when excited by earthquake loadings. A real earthquake time history recorded during the Loma earthquake of 1989 is used to excite the structures for verification purposes. Once a defective element is identified in a structure, the exact location of the defect can be identified with the proposed algorithm. The procedure is elaborated with the help of examples. The results indicate that the accuracy of the proposed NDE is much better than other currently available methods even when input excitation information was used for identification purposes. It is established that the proposed NDE method can be used for health assessment of existing structures on a continuing basis or just after a major natural event.
• Ling, X., & Haldar, A. (2004). Element level system identification with unknown input with Rayleigh damping. Journal of Engineering Mechanics, 130(8), 877-885.
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  Abstract: A novel system identification procedure is proposed for nondestructive damage evaluation of structures. It is a finite element-based time-domain linear system identification technique capable of identifying structures at the element level. The unique features of the algorithm are that it can identify a structure without using any input excitation information and it can consider both viscous and Rayleigh-type proportional damping in the dynamic models. The consideration of proportional damping introduces a source of nonlinearity in the otherwise linear dynamic algorithm. However, it will also reduce the total number of damping coefficients to be identified, reducing the size of the problem. The Taylor series approximation is used to transform a nonlinear set of equations to a linear set of equations. The proposed algorithm, denoted as the modified iterative least square with unknown input algorithm, is verified with several examples considering various types of structures including shear-type building, truss, and beams. The algorithm accurately identified the stiffness of structures at the element level for both viscous (linear) and proportional (nonlinear) damping cases. It is capable of identifying a structure even with noise-contaminated response information. An example shows how the algorithm could be used in detecting the exact location of a defect in a defective element. The algorithm is being developed further and is expected to provide an economical, simple, efficient, and robust system identification technique that can be used as a nondestructive defect detection procedure in the near future. © ASCE.
• Vo, P. H., & Haldar, A. (2004). Health assessment of beams - Experimental investigations. Journal of Structural Engineering (Madras), 31(1), 23-30.
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  Abstract: Experimental study on the health assessment of defect-free and defective beams recently completed at the University of Arizona is presented in this paper. The method can be extended to consider frame-type structures. The researchers at the University of Arizona proposed a finite-element-based time-domain system identification technique, known as ILS-UI, to detect defects at the local element level of structures. The algorithm does not need excitation information. The theoretical basis of the method is presented in the companion paper. The experimental verification of the method is presented in this paper. Defect-free and defective fixed-ended and simply supported beams are successfully identified by tracking the reduction of stiffness of elements. Initially, the optimal number of finite elements required to capture the dynamic behavior of a beam was studied. The ILS-SI method was then verified using computer generated theoretical response information. Experimental investigations were then carried out to verify the algorithm. Raw data obtained from the experiments failed to identify the elemental stiffness of the beam. Several post-processing techniques were used to remove many undesirable features from the records. The algorithm again failed to identify elemental stiffness of the beam even after the post-processing of the response data. Reasons behind the failure were then investigated. Errors in the amplitude and phase shifts were found to be the most critical factors for the non-convergence of the algorithm. Additional mitigation methods were then proposed to reduce the amplitude and phase shift errors that enabled the algorithm to successfully quantify the changes in the elemental stiffness. It can be concluded that the ILS-UI algorithm is validated using laboratory measured response information and it can be used as a method for detecting defects in structures.
• Haldar, A. (2003). Fabrication/construction deficiency evaluation - A novel approach. Journal of Structural Engineering (Madras), 30(1), 43-50.
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  Abstract: A probabilistic procedure is presented here to address commonly observed but mostly overlooked areas of fabrication and construction deficiency evaluation in civil engineering projects. The advancement in computational power has brought much sophistication to the analysis and design of engineering structures. However, similar sophistication is lacking in the evaluation of human error. Since fabrication and construction deficiencies are essentially human errors, the quality of constructed facilities may not show the same level of improvement. A deterministic evaluation of fabrication and construction deficiencies, in terms of load tests or inspection of the whole project, is not practical. Statistical sampling information can be used to establish the quality, and samples available in exposed areas can be used for this purpose. However, the raw sample data should be used judiciously. The appropriateness of the samples needs to be checked by conducting the χ2 test of homogeneity. The success rate parameter, obtained from the sampling information, is an important input variable in the proposed method. It is a random variable, and can be described by a standard Beta distribution. The parameters of the Beta distribution can be derived from the inspection outcomes. The hyperbinomial distribution, derived in this paper, would be the most appropriate distribution to capture the probabilistic characteristics of fabrication and construction deficiencies. The deficiencies can be quantified with a predetermined confidence level. The size of the samples is very important in the accuracy in the prediction. A large sample size is always beneficial, but the cost-benefit for the collection of large samples should be studied before any decision is made. An example demonstrates that a project with higher quality workmanship may require a smaller sample size to extract the desired probabilistic characteristics. Creative repair work can be used to satisfy all concerned parties. The method was used in several projects, and saved millions of dollars.
• Haldar, A., & Aktan, A. E. (2003). Definitions, quantitative indices and tools for measuring performance of constructed systems. Proceedings of the Structures Congress and Exposition, 343-344.
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  Abstract: Performance-based design concept in the construction industry was discussed. Performance-based design concept depends on many inter-connected issues including areas of applications, definition of performance, tool for measuring performance, quantitative indices that need to be satisfied, and performance under uncertainity. Load and resistance factor design (LRFD) concept is based on satisfying various limit state functions with predetermined risk or reliability levels. The performance of an existing structure can be established using information available at the time of design or using most recent information obtained from nondestructive health-assessment inspections.
• Haldar, A., & Huh, J. (2003). Uncertainty in the seismic response analysis. Proceedings of the Structures Congress and Exposition, 803-804.
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  Abstract: A reliability study was conducted to estimate uncertainty in seismic response analysis. The study deals with evaluation of structures subjected to short-duration dynamic and seismic loading. A finite element method (FEM)-based formulation was used in the study to model complex mechanical behaviours. A nonlinear FEM-based algorithm incorporating uncertainties in the random variables, including seismic loading, is proposed in the study to estimate the reliability of realistic structural systems. The nonlinear finite element-based hybrid method, proposed in the model will help to track the propagation of uncertainties in the seismic response analysis.
• Lee, S. Y., & Haldar, A. (2003). Reliability of frame and shear wall structural systems. II: Dynamic loading. Journal of Structural Engineering, 129(2), 233-240.
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  Abstract: A hybrid reliability evaluation approach is proposed, consisting of the response surface method, the finite-element method, the first-order reliability method, and the linear iterative scheme when the load is applied dynamically to a complicated structural system. The method is especially applicable for realistic structural systems consisting of different types of structural elements and materials. The method was specifically developed to evaluate the reliability of a steel frame and reinforced concrete shear wall structural system subjected to seismic loading. The unique feature of this algorithm is that the earthquake loading can be applied in the time domain, enabling a realistic representation of the seismic loading conditions. The steel members are represented by beam-column elements and the shear walls are represented by plate elements. The deterministic algorithm, discussed in detail in the companion paper, is then extended to consider the uncertainty in the random variables. The reliability of a frame without and with RC shear walls is evaluated for the serviceability performance functions. The results are verified using Monte Carlo simulation. The method estimates the probability of failure very accurately, and is very efficient compared to simulation. The algorithm can be used to estimate the reliability of complicated structural systems consisting of different types of structural elements and materials under dynamic including seismic loading applied in time domain.
• Seung, Y. L., & Haldar, A. (2003). Reliability of frame and shear wall structural systems. I: Static loading. Journal of Structural Engineering, 129(2), 224-232.
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  Abstract: An efficient and accurate algorithm is developed to evaluate the reliability of a steel frame and reinforced concrete shear wall structural system subjected to static loading. In a companion paper, the algorithm is extended to consider dynamic loading, including seismic loading. The concept integrates the finite-element method and the first-order reliability method, leading to a stochastic finiteelement-based approach. In the deterministic finite-element representation, the steel frame is represented by beam-column elements and the shear walls are represented by plate elements. The stiffness matrix for the combined system is then developed. The deterministic finite-element algorithm is verified using a commercially available computer program. The deterministic algorithm is then extended to consider the uncertainty in the random variables. The reliability of a steel frame with and without the presence of reinforced concrete shear walls is evaluated for the strength and serviceability performance functions. The results are verified using Monte Carlo simulations. The algorithm quantitatively confirms the beneficial effect of shear walls, particularly when the steel frame is weak in satisfying the serviceability requirement of lateral deflection. The algorithm can be used to estimate the reliability of any complicated structural system consisting of different structural elements and materials when subjected to static loading. The procedure will be useful in the performance-based design guidelines under development by the profession.
• Vo, P. H., & Haldar, A. (2003). Post-processing of linear accelerometer data in structural identification. Journal of Structural Engineering (Madras), 30(2), 123-130.
• Huh, J., & Haldar, A. (2002). Seismic reliability of non-linear frames with PR connections using systematic RSM. Probabilistic Engineering Mechanics, 17(2), 177-190.
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  Abstract: An effective, efficient, and robust reliability analysis algorithm is proposed for non-linear structures, where seismic loading can be applied in the time domain. The method is developed specifically for steel frame structures considering all major sources of non-linearity, including geometry, material, and partially restrained (PR) connections. The non-linearity due to PR connections is modeled by moment-relative rotation curves using the four-parameter Richard model. For seismic excitation, the loading, unloading, and reloading behavior at PR connections is modeled using moment-relative rotation curves and the Masing rule. The proposed algorithm intelligently integrates the response surface method, the finite element method, the first-order reliability method, and an iterative linear interpolation scheme. The uncertainties in all the random variables including the four parameters of Richard model are considered. Two unique features of the proposed algorithm are that (1) actual earthquake time histories can be used to excite structures in the presence of major sources of non-linearity and uncertainty and (2) it is possible to estimate the risk corresponding to both the serviceability and strength limit states. The algorithm is verified using the Monte Carlo simulation technique. The verified algorithm is first used to study the reliability of a frame structure in the presence of PR connections with different degrees of flexibility. Then the algorithm is used to estimate the reliability of a frame structure excited by 13 actual recorded earthquake time histories, 12 of them recorded during the Northridge earthquake of 1994. As expected, the reliabilities of the frame are found to be quite different, when excited by several time histories of the Northridge earthquake. © 2002 Elsevier Science Ltd. All rights reserved.
• Huh, J., & Haldar, A. (2002). Uncertainty in seismic analysis and design. Journal of Structural Engineering (Madras), 29(1), 1-7.
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  Abstract: A novel seismic analysis and design procedure under uncertainty is proposed. The catastrophic damage caused by recent earthquakes prompted the study. A stochastic finite element-based hybrid approach is proposed to evaluate the reliability of complicated real structures considering all major sources of uncertainty and nonlinearity. The algorithm rationally and effectively combines the concepts of the response surface method, the finite element method, the first-order reliability method, and the iterative linear interpolation scheme. The unique feature of the technique is that the seismic loading can be applied in the time domain, providing an alternative to the classical random vibration approach. The algorithm was elaborated by evaluating the probabilities of failure of braced and unbraced steel frames. Several design implications were identified. The information on the probability of failure can be used in the risk-consistent performance-based seismic design guidelines being developed by many countries. The selection of member sizes and arrangements as well as performance requirements can be established with the help of the proposed algorithm. This is very advanced reliability analysis technique for seismic loading applied in time domain explicitly considering the uncertainty associated with it. In the analysis and design of structures, uncertainty in seismic loading should not be overlooked.
• Huh, J., & Haldar, A. (2001). Stochastic finite-element-based seismic risk of nonlinear structures. Journal of structural engineering New York, N.Y., 127(3), 323-329.
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  Abstract: An efficient and accurate algorithm is proposed to evaluate risk in the time domain for nonlinear structures subjected to short duration dynamic loadings, especially seismic loading. The algorithm is based on the stochastic finite-element concept. Uncertainties in the dynamic and seismic excitation and the resistance-related parameters are incorporated by modeling them as realistically as possible. The proposed algorithm integrates the concepts of the response surface method, the finite-element method, the first-order reliability method, and the iterative linear interpolation scheme. Two iterative response surface schemes consisting of second-order polynomials (with and without cross terms) are proposed. A mixture of saturated and central composite design is used to assure both efficiency and accuracy in the algorithm. Sensitivity analysis is used to improve the efficiency further. The risk corresponding to both the serviceability and strength limit states is estimated. The unique feature of the algorithm is that actual earthquake loading time histories can be used to excite structures, enabling a realistic representation of the loading conditions. The algorithm is further clarified with the help of two examples.
• Salazar, A. R., & Haldar, A. (2001). Energy dissipation at PR frames under seismic loading. Journal of Structural Engineering, 127(5), 588-593.
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  Abstract: The major sources of energy dissipation, lateral deformation, and base shear in steel frames with partially restrained (PR) connections subjected to seismic loading are analytically studied. The analytical study confirms, in general, the behavior observed during experimental investigation: PR connections reduce the overall stiffness of frames, but add a major source of energy dissipation. It is observed, in general, that the maximum total base shear may significantly increase as the connection stiffness increases. The maximum top lateral displacement does not always increase with a decrease in the connection stiffness. The response under earthquake loading largely depends on the dynamic characteristics of both the structure and the earthquake excitation. Proper consideration of the stiffness of the PR connections and other dynamic properties is essential to predict the dynamic behavior, no matter how difficult the analysis procedure becomes.
• Reyes-Salazar, A., & Haldar, A. (2000). Dissipation of energy in steel frames with PR connections. Structural Engineering and Mechanics, 9(3), 241-256.
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  Abstract: The major sources of energy dissipation in steel frames with partially restrained (PR) connections are evaluated. Available experimental results are used to verify the mathematical model used in the study. The verified model is then used to quantify the energy dissipation in PR connections due to hysteretic behavior, due to the viscous damping and at plastic hinges if they are formed. Flow low damping values, the dissipation of energy at plastic hinges is comparable to that due to viscous damping, and increases as the frame approaches failure. The study confirms the general observations made in experimental investigations for steel frames with PR connections, however, proper consideration of the stiffness of PR connections and other dynamic behavior.
• Salazar, A. R., & Haldar, A. (2000). Structural responses considering the vertical component of earthquakes. Computers and Structures, 74(2), 131-145.
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  Abstract: The guidelines in the NEHRP Provisions and the Mexican Code regarding the effects of the vertical component of earthquakes on the response of frames are re-evaluated. Using a time domain nonlinear finite element program developed by the authors, the seismic responses of frames are evaluated realistically by simultaneously applying the horizontal and vertical components of earthquake motion. Three steel frames and 13 recorded earthquake motions are considered. The same response parameters are then estimated using the two codes, and their error is evaluated. It is found that, if the frames remain elastic, the NEHRP Provisions estimate the maximum horizontal deflection at the top of the frames and the bending moment in the columns very accurately; the Mexican Code overestimates them. If the frames develop plastic hinges, the Mexican Code conservatively overestimates them, but the NEHRP Provisions underestimate them in some cases. Both codes significantly underestimate the axial loads in columns. The underestimation increases as the frames develop plastic hinges. The underestimation is more for interior columns than for exterior columns. If the ratio R of the PGA of the vertical and horizontal components of an earthquake is higher than normal, the underestimation increases as R increases. The underestimation is not correlated with frame height. The vertical component may increase the axial load significantly. Since they are designed as beam-columns, the increase in the axial load will have a very detrimental effect on the performance of the columns. In light of the results obtained in this study, the design requirements for the vertical components need modification. At the very least, further study is required.
• Haldar, A., & Zhao, Z. (1999). Fatigue reliability updating using NDE. Structures Congress - Proceedings, 821-824.
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  Abstract: Using a linear elastic fracture mechanics (LEFM) approach, the fatigue reliability is estimated considering all major sources of uncertainty, including uncertainties in nondestructive inspection outcomes. The fatigue reliability is then updated using uncertainty-filled information from nondestructive inspections, as it becomes available. The updated information on the reliability is used as a decision making tool regarding what to do next, in terms of whether to do nothing, reschedule the next inspection to an earlier data, or immediately repair or replace the damaged element. The procedure is explained with the help of an example.
• Huh, J., Mehrabian, A., Haldar, A., & Salazar, A. R. (1999). Critical review of fully probabilistic design for seismic loadings. Structures Congress - Proceedings, 480-483.
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  Abstract: The necessity of fully probabilistic design for short duration dynamic loadings including seismic loading is critically reviewed. Implementation of fully probabilistic design for static loadings has had limited success, particularly in cases where the limit state functions are available in explicit form. However, in most cases of practical significance, the limit state functions are not available even for static loadings. For nonlinear static loadings and linear or nonlinear dynamic or seismic loadings, the limit state function is implicit, and can only be expressed in algorithmic form, e.g. using the finite element algorithm. The issues and challenges of fully probabilistic design for implicit limit state functions emphasizing seismic loading are discussed. A method is proposed and the procedure is explained with the help of an example.
• Reyes-Salazar, A., & Haldar, A. (1999). Nonlinear seismic response of steel structures with semi-rigid and composite connections. Journal of Constructional Steel Research, 51(1), 37-59.
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  Abstract: The nonlinear seismic responses of steel frames with fully restrained, partially restrained and composite connections are evaluated and compared in terms of the maximum interstory and maximum top lateral displacements. Steel frames are usually analyzed assuming all the connections are fully restrained. However, considering the practical design aspects of connections, this is rarely true. This practice introduces unintended flexibility in the frame. Using a nonlinear time domain seismic analysis algorithm developed by the authors, three steel frames are excited by 13 earthquake time histories. Twelve of them were recorded during the Northridge earthquake of 1994. Any one of these 12 earthquake time histories can be used to represent the Northridge earthquake in future designs. To define the rigidity of a connection, a parameter called the T ratio is introduced. It is the ratio of the moment the connection would have to carry according to the beam line theory and the fixed end moment of the girder. Initially, the T ratio of all the connections is assumed to be 0.9, making them fully restrained. The results indicate that this assumption is inappropriate and gives unconservative responses depending upon which time history of the same earthquake is being used. Several frames with a T ratio of 0.95 developed very large lateral displacements causing instability, although they behaved properly when the ratio was assumed to be 1.0. For composite connections, slab steel has a significant beneficial effect on the overall structural response. It increases the T ratio, making it closer to the FR connection. Even for composite connections with a T ratio of 0.95, the frames developed large lateral displacement. Further parametric study indicates that, at least for seismic analysis, PR or composite connections should be designed for a T ratio as close to 1 as possible to represent an FR connection. Otherwise, the lateral displacement failure criterion should also be checked for less than ideal FR connection conditions. Improvements in both the analysis and design of steel frames are necessary to make them more seismic load tolerant.
• Chowdhury, M. R., Wang, D., & Haldar, A. (1998). Reliability assessment of pile-supported structural systems. Journal of Structural Engineering, 124(1), 80-88.
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  Abstract: A performance-mode (PM)-based evaluation procedure is proposed to determine the probability of unsatisfactory performance (UP) for two-dimensional (2-D) and three-dimensional (3-D) systems involving pile-supported dams. This methodology includes ductile behavior of individual piles for the strength mode. It also examines the 3-D effects on the bounds for the series-parallel system. The procedure is an extension of the reliability method presented to compute the system probability of UP of pile-supported structures using brittle-element behavior. Lateral and vertical deflections are the limit states of the pile cap that provide the system-level probability of UP for the serviceability limit state. The element-level probability of UP for strength and system-level probability of UP serviceability are combined to evaluate the bounds for the load-case specific system probability of UP. Finally, the overall system probability of UP is evaluated considering the contributions of all load cases combined. The procedure is illustrated wilh examples, and the bounds for the system probability of UP are evaluated. The results indicate that the bounds of probability of UP for the example are narrower for ductile behavior than for brittle behavior. A 3-D problem correctly recognizes a number of significant PM that are absent in the 2-D approximation.
• Wang, D., & Haldar, A. (1997). System identification with limited observations and without input. Journal of Engineering Mechanics, 123(5), 504-510.
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  Abstract: A time domain system identification technique is proposed to estimate the stiffness and damping parameters, at the element level, of a structure excited by unknown or unmeasured input forces. The unknown input forces could be of any type, including seismic loading. The unique feature of this technique is that it does not require response measurements at all dynamic degrees of freedom of structure. This new procedure is a combination of an iterative least-squares procedure with unknown input excitations (ILS-UI) proposed earlier by the writers, and the extended Kalman filter method with a weighted global iteration (KF-WGI). The new procedure is denoted by the writers as ILS-EKF-UI. The uncertainty in the output responses is considered, and its effect on the accuracy of the identified parameters is analyzed. The efficiency, accuracy, and robustness of the proposed algorithm are illustrated by numerical examples. The accuracy of the proposed ILS-EKF-IU procedure is of the same order as that of ILS-UI; however, it requires a longer response measurement. This is expected since ILS-EKF-UI identifies a structure using less information than the ILS-UI does. However, the efficiency of the new algorithm can be improved by considering a shorter duration of response measurements for the ILS-UI procedure and a longer duration for the KF-WGI without compromising the accuracy of the identified parameters.
• Wang, D., Chowdhury, M. R., & Haldar, A. (1997). System reliability evaluation considering strength and serviceability requirements. Computers and Structures, 62(5), 883-896.
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  Abstract: A robust system reliability evaluation method is proposed for aging redundant structures. Pile-supported structures commonly used for dams are specifically addressed. The individual pile behavior is considered to be brittle-type and the group behavior is considered to be parallel-type. Both strength and serviceability performance modes are considered. Using the advanced first-order second-moment reliability method, the element-level reliability indices are calculated for individual piles for several strength limit states. The system-level reliability indices of the pile group are calculated considering the lateral and vertical deflection limit states. Using the performance mode approach, which is referred to as the failure mode approach in the literature, a procedure is proposed to identify significant performance modes of the system by combining the element-level and system-level reliabilities. The bounds of the system reliability are then estimated. The procedure is first verified using information from load tests. The method is then applied to estimate the bounds of system reliability for a pile-supported dam. Identification of the significant performance modes becomes easier using the proposed method. It is observed that the values used for the allowable lateral and vertical deflections are critical in the overall system reliability evaluation. The lower and upper bounds of the system reliability are observed to be narrow for the examples considered in the study. The proposed procedure significantly improves the state of the art in the evaluation of system reliability of pile-supported structures. Copyright © 1996 Elsevier Science Ltd.
• Haldar, A., & Gao, L. (1996). Reliability evaluation using SFEM. Probabilistic Mechanics and Structural and Geotechnical Reliability, Proceedings of the Specialty Conference, 166-169.
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  Abstract: The use of the finite element method in the safety evaluation of a structure is discussed. The method is based on the Advanced First Order Second Moment reliability analysis procedure. Several sources of nonlinearities, including geometric and material, are incorporated into the algorithm. Special features like flexibility of the connections are also incorporated without losing the basic simplicity. Since the procedure is based on several deterministic finite element analyses of a structure, it is extremely robust and can capture all the essential features that need to be considered in any deterministic finite element analysis.
• Haldar, A., & Zhao, Z. (1996). Reliability-based maintenance strategy using NDI. Probabilistic Mechanics and Structural and Geotechnical Reliability, Proceedings of the Specialty Conference, 364-367.
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  Abstract: Reliability-based inspection and maintenance strategies are proposed to mitigate fatigue risk of a structure. This is based on the fatigue reliability method already developed by the authors. Using Bayesian updating approach, the fatigue risks are updated after each inspection, and fatigue control curves are proposed. The information is used to propose repair and replacement criteria. If rescheduling the next inspection to an earlier date is desirable, the model suggests the time for the next inspection. After an inspection, the method helps to decide whether to do nothing, inspect more frequently, or repair or replace the inspected parts.
• Zhao, Z., & Haldar, A. (1996). Bridge fatigue damage evaluation and updating using non-destructive inspections. Engineering Fracture Mechanics, 53(5), 775-788.
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  Abstract: A method is proposed to mitigate fatigue damage using information from non-destructive inspections. In spite of improvements in the design of fatigue-sensitive structures, periodic non-destructive inspections are still required by the profession. A linear elastic fracture mechanics-based reliability model is proposed which incorporates uncertainties from many different sources, including uncertainty in the results obtained from the non-destructive inspections. Regardless of whether or not it detects any cracks, each inspection provides additional information and the underlying fatigue reliability needs to be updated after each inspection. The updated information on the reliability can be used as a decision making tool as what to do next, in terms of whether to do nothing, reschedule the next inspection at an earlier date, or repair or replace the structure immediately. The application potential of the method is demonstrated with the help of examples. It is shown that the proposed method is much superior to the current S-N curve-based AASHTO method and can be used as an alternative to it.
• Chowdhury, M. R., Wang, D., & Haldar, A. (1995). System reliability evaluation of pile-founded structures. Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2, 931-941.
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  Abstract: Using the performance mode approach (which is referred as the failure mode approach in the literature), a system reliability evaluation procedure is proposed for pile-founded structures. Both strength and serviceability performance modes are considered. The individual pile behavior is considered to be brittle-type and the group behavior is considered to be parallel-type. Using the advanced first-order second-moment method, the element-level probability of unsatisfactory performance of a pile is calculated for the strength performance mode, and the system-level probability of unsatisfactory performance of the pile cap is calculated for the serviceability performance mode. A procedure to identify significant performance modes is proposed, and the bounds for the system probability of unsatisfactory performance are estimated. The procedure is explained with the help of an example. The proposed procedure significantly improves the state of the art in the evaluation of system reliability of pile-supported structures.
• Gao, L., & Haldar, A. (1995). Nonlinear seismic analysis of space structures with partially restrained connections. Microcomputers in civil engineering, 10(1), 27-37.
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  Abstract: An efficient and robust finite-element-based method for estimating nonlinear responses of complex three-dimensional structures with partially restrained connections under dynamic and seismic loading is presented. The method is developed using the assumed stress-based finite-element method in which the tangent stiffness can be expressed in explicit form and fewer elements are needed to model a structure. Geometric and material nonlinearities and the nonlinear behavior of partially restrained connections are considered. For the dynamic and seismic analyses, three major sources of damping are considered. They are viscous damping, hysteretic damping in the PR connections, and the hysteretic damping at the plastic hinges, if plastic hinges are developed in the structure. It is observed from the examples considered in this study that proper consideration of PR connections is essential in modeling the realistic dynamic and seismic behavior of structures. Numerical results show that the presence of partially restrained connections may not cause failure of a structure due to insufficient strength but may make serviceability constraints, e.g., the lateral deformation, more critical.
• Gao, L., & Haldar, A. (1995). SFEM-based evaluation of strength and serviceability requirements. Proceedings of Engineering Mechanics, 2, 1127-1130.
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  Abstract: Using a nonlinear stochastic finite element method already developed by the authors, the reliability of steel frames with partially restrained connections is evaluated using the strength and serviceability limit states. It is observed that steel frames with partially restrained connections designed for strength alone may not satisfy the serviceability requirements, making serviceability the governing limit state.
• Gao, L., & Haldar, A. (1995). Safety evaluation of frames with PR connections. Journal of structural engineering New York, N.Y., 121(7), 1101-1109.
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  Abstract: An efficient nonlinear stochastic finite-element method is proposed for the design of frame structures, specifically applicable to steel structures. Nonlinearities due to geometry, material, and partially restrained (PR) connections are considered in the algorithm. The efficiency, robustness, desirability, and application potential of the method are demonstrated. The proposed algorithm can be used an alternative to the currently available methods to analyzed and design frames, and to evaluate the corresponding reliabilities.
• Haldar, A., & Zhao, Z. (1995). Fatigue risk assessment procedures. American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 304, 453-460.
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  Abstract: Fatigue reliability evaluations are presented which specifically use the S-N curve and linear elastic fracture mechanics (LEFM) approaches. The basic random variables in both approaches are identified and their statistical characteristics are quantified. A parametric sensitivity analysis is also performed. It is shown with the help of an example that the two approaches produce similar results.
• Haldar, A., & Zhao, Z. (1995). Reliability-based inspection strategy for fatigue risk management. Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2, 215-222.
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  Abstract: A reliability-based inspection strategy is proposed by incorporating uncertainties in nondestructive inspections into the fatigue reliability method previously developed by the authors. The additional sources of uncertainty incorporated are the detectability and the accuracy of the nondestructive inspection. The inspection outcomes are classified into three categories: nondetection, detection without size measurement, and detection with size measurement. A strategy is proposed for estimating the optimal time interval to the next inspection. If rescheduling the next inspection to an earlier date is desirable, the model suggests the time for the next inspection.
• Wang, D., & Haldar, A. (1994). Element-level system identification with unknown input. Journal of Engineering Mechanics, 120(1), 159-176.
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  Abstract: A finite element-based time domain system identification procedure is proposed to evaluate existing large structural systems at the element level. The procedure does not need any information on the input excitation forces. Since the input exciting forces are not required, there is no restriction on the type of exciting force, only a small number of observation time points are required and no information is required on the modal properties of the structure. The unknown exciting forces can be applied at the ground level representing the seismic excitation. The procedure is particularly applicable to identifying an existing structure. The errors in the estimation of the parameters are considerably smaller than those in the other methods currently available in the literature. The proposed method is very economical, simple, and robust.
• Zhao, Z., Haldar, A., & Breen Jr., F. L. (1994). Fatigue-reliability evaluation of steel bridges. Journal of structural engineering New York, N.Y., 120(5), 1608-1623.
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  Abstract: The fatigue reliability of steel-bridge components is evaluated. The most commonly used S-N curve-based American Association of State Highway and Transportation Officials (AASHTO) method is considered first. The limit-state equation and the uncertainty associated with all the basic random variables are quantified. Using the advanced first-order second-moment method, the corresponding probability of failure is calculated in terms of the reliability index. It is observed that the reliability index is very similar to other design problems involving steel structures. Since the AASHTO approach cannot incorporate the crack-size information even if it is known at the time of evaluation, an alternative linear elastic fracture mechanics (LEFM) method is proposed. The corresponding limit-state equation and the basic variables are identified, and the uncertainties associated with them are quantified. The reliability index is calculated similarly. For comparison purposes, the reliability indexes according to the AASHTO and LEFM approaches are evaluated for full-penetration butt welds in the tension flange of a steel-box girder used in a public transportation system.
• Zhao, Z., Haldar, A., & Breen Jr., F. L. (1994). Fatigue-reliability updating through inspections of steel bridges. Journal of structural engineering New York, N.Y., 120(5), 1624-1642.
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  Abstract: A reliability-based fatigue-damage evaluation procedure developed in the companion paper is extended in this paper to incorporate information from nondestructive inspections (NDI). Since inspections are required at regular intervals, the results from these inspections can be used for fatigue maintenance of steel bridges. The sensitivity and capability of some of the inspection methods, including ultrasonic inspection, are investigated. Inspection information is beneficial; however, it adds uncertainty to the fatigue-evaluation process. The detectability and the accuracy are two additional sources of uncertainty in the NDI. The uncertainties in them are quantified. The detection events are classified into three cases, no crack detection, crack detection but without size measurement, and crack detection with the crack-size measurement. Using the information from k-inspections, the distributions of the basic random variables and the corresponding reliability index are updated.
• Haldar, A., & Reddy, R. K. (1992). A random-fuzzy analysis of existing structures. Fuzzy Sets and Systems, 48(2), 201-210.
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  Abstract: Two approaches are proposed to estimate the reliability of existing structures by considering both the randomness in some of the design parameters and the fuzzy imprecision in some other parameters representing the in-place condition of the aged structures. In the first approach, the fuzzy imprecision is transformed into random uncertainty using the entropy concept, and the reliability of existing structures is estimated using well-established theories of probability. In the second approach, a hybrid approach in the random-fuzzy domain is used to evaluate the reliability using an α-level concept. The multiple fuzzy variables case is also considered. Both discrete and continuous fuzzy variables are considered. The results obtained from the proposed approaches are compared with other techniques available in the literature whenever possible. Both methods are applied to civil structural engineering problems in this paper. The results obtained are very encouraging and demonstrate the applicability and robustness of the algorithms. © 1992.
• Haldar, A., & Zhou, Y. (1992). Reliability of geometrically nonlinear PR frames. Journal of Engineering Mechanics, 118(10), 2148-2155.
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  Abstract: An efficient stochastic finite element method (SFEM) is proposed for the reliability analysis of frame structures with geometric and nonlinearities. The assumed stress field approach is used in computing nonlinear structural responses and the corresponding response gradients. The comparison of the reliability indices among the linear structure, nonlinear structure and nonlinear structure with flexible connections are stressed in the numerical example.
• Haldar, A., & Zhou, Y. (1992). Reliability of nonlinear frame structures by SFEM. Probabilistic Mechanics and Structural and Geotechnical Reliability, Proceedings of the Specialty Conference, 336-339.
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  Abstract: A method is proposed for the reliability analysis of nonlinear frame structures with flexible connections. The uncertainty of a connection is represented by a group of random moment-relative rotation curves. A random index parameter is introduced to consider the randomness in the connection behavior. The assumed stress-based stochastic finite element method is used for the reliability estimation. The reliability of frame structures with rigid connections, deterministic flexible connections and random flexible connections is stressed in this paper.
• Mahadevan, S., & Haldar, A. (1991). Practical random field discretization in stochastic finite element analysis. Structural Safety, 9(4), 283-304.
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  Abstract: Stochastic finite element-based reliability analysis is applied to structures with distributed parameters that can be modeled as random fields. In this method, reliability is estimated through analytical computation of the sensitivity of stochastic response to the basic random variables. The random fields are discretized into sets of correlated random variables using two methods of discretization. The sensitivity measures are further used to selectively consider only a few of the distributed parameters as random fields, to ensure computational efficiency. The issue of choosing the appropriate mesh for the discretization of the random field is addressed through mesh refinement studies. With the help of three numerical examples, the paper examines the effects of the correlation characteristics of the random field on discretization and reliability analysis, and develops guidelines for efficient application of stochastic finite element analysis to structures with distributed parameters. © 1991.
• Mahadevan, S., & Haldar, A. (1991). Reliability-based optimization using SFEM. Lecture Notes in Engineering, 241-250.
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  Abstract: Consideration of element level reliabilities in design optimization ensures a distribution of weight such that there is uniform risk in the structure failure modes and ensures overall safety. Therefore an optimization algorithm that considers both types of reliability is desirable. The Stochastic Finite Element Method (SFEM) appears capable of efficiently solving the aforementioned problems. Given a probabilistic description of the basic parameters, SFEM is able to compute the stochastic response of the structure in terms of either the response statistics such as mean, variance, etc. or the probability of failure considering a particular limit state. This is done by keeping account of the variation of the quantities computed at every step of the deterministic analysis, in terms of the variation of the basic variables. This capability makes SFEM attractive for application to reliability-based optimum design of large structures. Such an optimization procedure is presented in this paper using SFEM-based reliability analysis, and illustrated with the help of a numerical example.
• Haldar, A., & Kanegaonkar, H. B. (1989). Stochastic transients of a deepwater compliant platform. Proceedings of the International Offshore Mechanics and Arctic Engineering Symposium, 1(8 th), 191-198.
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  Abstract: The transient dynamic behavior of a guyed tower platform with nonlinear stiffness subject to random wave loading is investigated using a non-Gaussian closure technique. The individual storm wave loadings are represented by rational spectra. The stiffness nonlinearity is expressed in terms of analytical function. The differential equation of motion is expressed as a set of first order stochastic equations. Ito's rule of stochastic differentials is used to develop ordinary differential equations of moments of the response. The moments are obtained by numerical solution of the equations. A new storm is considered to be acting on the structure when the structure is vibrating in a steady state from the previous storm. The transient behavior of the stochastic response parameters is studied. It is found that the guyline tensions vary significantly during the transient state. Sudden drops and increases in the tensions leading to jerk or snap loading will also affect the fatigue of the guylines. The time-dependent probability distribution of the response in the transient state is seen to vary significantly.
• Haldar, A., & Ker-Ming, N. (1989). Elasto-plastic large deformation analysis of PR steel frames for LRFD. Computers and Structures, 31(5), 811-823.
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  Abstract: An efficient second-order finite element-based method is presented here considering geometric and material nonlinear behavior of steel frames with nonlinear flexible connections and local plasticity effects. The assumed stress method is used to derive the governing equations which satisfy joint equilibrium and displacement compatibility conditions. An explicit form of the tangent stiffness matrix of the structure is obtained that makes the proposed method extremely efficient in nonlinear analysis. In deriving governing equations for large deformation, each element is characterized as a beam-column which undergoes arbitrary large rigid displacement but small relative displacement. The behavior of flexible connections is represented by an exponential function. In solving the nonlinear equations, the Newton-Raphson method with arc-length control is used in tracing the post-buckling behavior. Several numerical examples are given to demonstrate the robustness, accuracy and efficiency of the proposed method. © 1989.
• Mahadevan, S., & Haldar, A. (1989). Efficient algorithm for stochastic structural optimization. Journal of structural engineering New York, N.Y., 115(7), 1579-1598.
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  Abstract: A stochastic structural optimization procedure using element-level reliabilities as constraints is proposed here. The procedure is robust and efficient and closely resembles the practical approach used in design offices. The procedure is developed in modules which can be linked and unlinked Element-level reliabilities are estimated using the stochastic finite element method for Monte Carlo simulation with variance reduction techniques whenever necessary. The method can consider different limit states with different desired levels of reliability as well as the system reliability as constraints, resulting in a balanced distribution of weight. A constrained optimization algorithm is used which is tailored to the information and the requirements of the structural optimization problem considered here. The algorithm contains a simple and efficient search procedure that uses variable, discrete step sizes. Several alternatives for reliability analysis and trial structure selection, and strategies for reduction of the number of constraints are included and explained with the help of numerical examples to show th desirability of the proposed method.
• Mahadevan, S., & Haldar, A. (1989). Structural optimization based on component-level reliabilities. Array, 1887-1894.
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  Abstract: A minimum-weight optimum design procedure is proposed including the reliabilities of various elements in a structure as constraints. The reliability indices corresponding to the various limit states are computed using the Stochastic Finite Element Method, and are required to be within a desired narrow range. A derivative-free constrained optimization algorithm with variable discrete step sizes is used to obtain the optimum design. Both serviceability and ultimate limit states can be incorporated; also, different levels of risk can be assigned to different limit states indicating their relative importance. The procedure can include system reliability constraints, has options for the addition or deletion of constraints, and can use design groups of similar members for computational efficiency.
• Kanegaonkar, H. B., & Haldar, A. (1988). Mooring line fatigue in an offshore guyed tower. International Journal of Fatigue, 10(3), 199-205.
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  Abstract: A probabilistic method is presented for the fatigue analysis of the mooring lines of a guyed tower. The wave loading is idealized as the first component of a two-dimensional Markov process. Using Ito's rule of stochastic differentials, differential equations for moments up to the fourth order are obtained, and these are solved using numerical techniques for both Gaussian and non-Gaussian methods. The displacement response is modelled as a mixture distribution. The probability distribution of guyline tension is then estimated. The probability density for peak guyline tensions is estimated by mapping a Gaussian process into the non-Gaussian process of guyline tensions using the double inversion technique and estimating level crossings. The tension fatigue is estimated using Palmgren-Miner's rule. It is shown that the fatigue damage estimated using non-Gaussian closure is greater than that estimated using Gaussian closure. © 1988.
• Mahadevan, S., & Haldar, A. (1988). Stochastic finite element analysis of frames with flexible connections. Array, 169-172.
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  Abstract: A procedure is proposed in this paper for the stochastic finite element analysis of frames with stochastic connection rigidity. A beam-column element is used to simulate the connection and its bending stiffness is assumed to be equal to the tangent stiffness of the connection, given by the slope of the moment-rotation curve. The randomness in the rigidity is then taken into account in the subsequent stochastic analysis of the frame. The proposed method is illustrated with the help of a numerical example.
• Nee, K., & Haldar, A. (1988). Elastoplastic nonlinear post-buckling analysis of partially restrained space structures. Computer Methods in Applied Mechanics and Engineering, 71(1), 69-97.
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  Abstract: A method is proposed here to analyze a space structure with large deformation, partially restrained connections, and material nonlinearities using the plastic hinge concept. The assumed stress method is used to derive an explicit form of tangent stiffness satisfying joint equilibrium and displacement compatibility. The unique feature of the method is that it is extremely efficient since the tangent stiffness is expressed in an explicit form and can easily be modified to consider different factors. The method can be used to study both the pre- and post-buckling behavior of space structures. It is verified with experimental and numerical results available in the literature. The robustness of the algorithm is confirmed by applying it to analyze several problems of practical importance. The method is robust yet simple, accurate, and economical. © 1988.
• Haldar, A., & Chern, S. (1987). Soil-structure interaction in earthquake-induced liquefaction.. Earthquake engineering. Proc. 5th Canadian conference, Ottawa, 1987, (Balkema), 493-499.
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  Abstract: A method is proposed to estimate damage to a structure due to earthquake-induced liquefaction considering the effect of soil-structure interaction. The damage is estimated in terms of differential settlement. The structural rigidity can significantly reduce the extent of damage to a structure. The redistribution of vertical loads due to uneven settlement of the foundations due to earthquake shaking can be modeled effectively by considering the interaction between the structure and the soil. A finite element-based computer program is written specifically for this purpose. The methodology is described with the help of an example.-Authors
• Haldar, A., & Chern, S. (1987). UNCERTAINTY IN DYNAMIC ANISOTROPIC STRENGTH OF SAND.. Journal of geotechnical engineering, 113(5), 528-533.
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  Abstract: The uncertainty associated with the estimation of the in situ dynamic shear strength tau //R of a deposit with static shear stress acting at the plane of failure (anisotropic conditions) is the subject of this paper. Whether there is shear stress reversal or not, anisotropically consolidated samples strain progressively during cyclic loading. Because a cyclic anisotropically consolidated sample can fail before the pore water pressure reaches the confining pressure, the load cycles required to cause pore pressure equal to the confining pressure cannot be used as a parameter in the model of anisotropic shear strength. Considering all the failure criteria, the failure criterion proposed by C. S. Chang, et al. is considered here. The statistical model is developed in two steps: first, the cyclic shear strength tau //R is estimated in terms of the anisotropic strength parameter R//a under laboratory conditions; second, the laboratory relationship thus obtained is modified to represent in situ conditions.
• Haldar, A., & Kanegaonkar, H. B. (1987). Probabilistic nonlinear dynamics of deepwater compliant platforms.. IN: OTC '87 PROC., NINETEENTH ANNUAL OFFSHORE TECHNOL. CONF., (HOUSTON, U.S.A.: APR. 27-30, 1987), 1 , Richardson, U.S.A., Offshore Technol. Conf., 1987, Paper OTC 5413, 461-468.
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  Abstract: A probabilistic technique for analysis of a guyed tower is presented taking into account the nonlinear behaviour of guylines. The wave loading is expressed as an output of normal white noise passing through a filter. Using Ito's method of stochastic differentials, a system of moment equations is developed and is closed at the fourth moment level. The equations are solved in the time domain to obtain the transient and stationary responses. It is shown that the response is non Gaussian at higher sea states.
• Haldar, A., & Kanegaonkar, H. B. (1987). STOCHASTIC FATIGUE OF NONLINEAR OFFSHORE STRUCTURAL SYSTEMS.. Array, v 1p.
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  Abstract: Nonlinearities in the wave loading due to nonlinear wave kinematics and free surface fluctuation are considered for a jacket-type platform. The first four moments of the response are estimated using the mean square estimation technique via conditional distribution. Nonlinear stiffness is considered for a guyed tower system. Approximating the loading by the ARMA process, Ito stochastic differential equations for the response moments are solved up to fourth order where the system of equations is closed by neglecting the fifth and higher order cumulants. The response moments are considered to be a mixture of Gaussian and non-Gaussian distributions. By mapping a Gaussian process into this response process, the expected rate of positive crossings is estimated, leading to the probability density of the peaks. Palmgren-Miner's hypothesis for fatigue damage accumulation is used. It is shown that the conventional method is unconservative when the response distribution is leptokurtic.
• Kanegaonkar, H. B., & Haldar, A. (1987). NON-GAUSSIAN CLOSURE FOR STOCHASTIC RESPONSE OF GEOMETRICALLY NONLINEAR COMPLAINT PLATFORMS.. Proceedings of the International Offshore Mechanics and Arctic Engineering Symposium, 1, 45-52.
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  Abstract: A method is proposed to estimate the stochastic response of compliant offshore platforms with geometric nonlinearity based on non-Gaussian closure. For guyed towers with clump weight, the nonlinearity in stiffness is of the softening type. The random wave loading is expressed in terms of a rational spectrum. The combined load-structure system is thus Markovian. Using Ito's rule for stochastic differentiation, differential equations for moments up to the fourth order are developed. The system of equations is closed by considering the fifth and sixth cumulants to be zero. The stationary response is obtained by solving the system of nonlinear algebraic equations. It is observed that the Gaussian closure method is inadequate for defining the complete probabilistic characteristics of the response.
• Kanegaonkar, H. B., & Haldar, A. (1987). NON-GAUSSIAN RESPONSE OF OFFSHORE PLATFORMS: DYNAMIC.. Journal of structural engineering New York, N.Y., 113(9), 1882-1898.
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  Abstract: A hybrid method, consisting of spectral and probabilistic analysis techniques, is proposed to evaluate the dynamic response characteristics of offshore platforms considering nonlinear wave kinematics and free-surface fluctuation effects. The effect of nonlinear wave kinematics and intermittent loading is that the wave loading is non-Gaussian. The response of platforms to such non-Gaussian loading will be non-Gaussian. A combination of spectral and probabilistic analyses is developed to estimate the response up to the fourth moment. The probability distribution of the response is estimated as a mixture of Gaussian distribution and shifted exponential distribution.
• Kanegaonkar, H. B., & Haldar, A. (1987). NON-GAUSSIAN RESPONSE OF OFFSHORE PLATFORMS: FATIGUE.. Journal of structural engineering New York, N.Y., 113(9), 1899-1908.
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  Abstract: A fatigue analysis procedure is proposed for offshore platforms where the response is non-Gaussian due to nonlinear wave kinematics and free-surface fluctuations. The non-Gaussian distribution of the stress process is considered to be a mixture of Gaussian and shifted exponential distributions. The level crossings of this process are estimated considering it a translation process, and the probability density function of the peaks is estimated numerically. Using Palmgren-Miner's rule for fatigue damage accumulation, the total cumulative damage over the long-term wave climate is estimated. It is shown that at higher sea states, where the effect of intermittent loading is significant, the probability density function of the peaks of the stress deviates significantly from the normally used Rayleigh density.
• Kanegaonkar, H. B., & Haldar, A. (1987). Non-Gaussian response of offshore platforms: dynamic.. J. STRUCT. ENGNG. (ASCE), 113(9 , Sep. 1987, p.1882-1898.).
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  Abstract: A hybrid method, consisting of spectral and probabilistic analysis techniques, is proposed to evaluate the dynamic response characteristics of offshore platforms considering nonlinear wave kinematics and free surface fluctuation effects. The effect of nonlinear wave kinematics and intermittent loading is that the wave loading is non Gaussian. The response of platforms to such non Gaussian loading will be non Gaussian. A combination of spectral and probabilistic analyses is developed to estimate the response up to the fourth moment. The probability distribution of the response is estimated as a mixture of Gaussian distribution and shifted exponential distribution. With the help of an example, it is shown that the free surface fluctuations have a significant effect on the response. The skewness and kurtosis are shown to increase with an increase in significant wave height. The probability distribution is shown to deviate from the normally assumed Gaussian distribution, particularly at the tails commonly found in full scale measurements.
• Kanegaonkar, H. B., & Haldar, A. (1987). Non-Gaussian response of offshore platforms: fatigue.. J. STRUCT. ENGNG. (ASCE), 113(9 , Sep. 1987, p.1899-1908.).
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  Abstract: A fatigue analysis procedure is proposed for offshore platforms where response is non Gaussian due to nonlinear wave kinematics and free surface fluctuations. The non Gaussian distribution of the stress process is considered to be a mixture of Gaussian and shifted exponential distributions. The level crossings of this process are estimated considering it as a translation process, and the probability density function of the peaks is estimated numerically. Using Palmgren Miner's rule for fatigue damage accumulation, the total cumulative damage over the long term wave climate is estimated. It is shown that at higher sea states, where the effect of intermittent loading is significant, the probability density function of the peaks of the stress deviates significantly from the normally used Rayleigh density. The assumption of Rayleigh density for peaks at higher sea states is shown to be unconservative, and the unconservatism increases with an increase in significant wave height. Since field observations confirm that the dynamic response of offshore platforms is non Gaussian, the method proposed could be used to check the fatigue design of offshore platforms to avoid overestimating the fatigue life.
• Kanegaonkar, H. B., & Haldar, A. (1987). Non-Gaussian stochastic response of nonlinear compliant platforms. Probabilistic Engineering Mechanics, 2(1), 38-45.
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  Abstract: A moment function method is presented to estimate the stochastic response of compliant offshore platforms with nonlinearity in stiffness based on non-Gaussian closure. For guyed towers with clump weight, the nonlinearity in stiffness is of the softening type. The random wave loading is expressed in terms of a rational spectrum, making the system Markovian. Using Ito's rule for stochastic differentiation, differential equations for moments up to the fourth order are developed. The system of equations is closed by considering the fifth and sixth cumulants to be zero. For stationary response, differential equations become algebraic equations. The moments are obtained by solving the system of nonlinear algebraic equations. It is observed that the Gaussian closure method is inadequate for defining the complete probabilistic characteristics of the response. © 1987.
• Haldar, A., & Chern, S. (1986). Probabilistic prediction of pore pressure-induced settlement for isotropically and anisotropically consolidated deposits.. Geologia Applicata e Idrogeologia, 21(3), 9-22.
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  Abstract: Probabilistic models are proposed to estimate pore pressure-induced settlement of both isotropically and anisotropically consolidated saturated sand deposits subjected to earthquake loadings. Field observations during earthquake loadings are used to develop the basic numerical model for isotropic soils, while experimental laboratory results are used for anisotropic soils. -Authors
• Haldar, A., & Kanegaonkar, H. B. (1986). Stochastic fatigue response of jackets under intermittent wave loading.. IN: OTC '86 PROC. EIGHTEENTH ANNUAL OFFSHORE TECHNOL. CONF., (HOUSTON, U.S.A.: MAY 5-8, 1986), 4 , Richardson, U.S.A., Offshore Technol. Conf., 1986, Paper OTC 5332, 377-386.
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  Abstract: A combination of spectral and probabilistic analysis techniques is proposed to estimate the fatigue damage of jackets subjected to intermittent wave loading. The resulting non Gaussian response process is considered to be a mixture of Gaussian and shifted exponential. It is shown that the peak density deviates significantly from the Rayleigh and Gaussian response assumption is unconservative for fatigue damage evaluation at higher sea states.
• Haldar, A., & Luettich, S. M. (1986). RISK OF STRUCTURAL DAMAGE IN LIQUEFACTION.. Array, 1, 575-586.
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  Abstract: A probabilistic method is proposed here to evaluate the risk of structural damage due to earthquake-induced liquefaction by considering liquefaction as a subsidence problem. The model considers all the site-related soil properties and geometric conditions, the proposed type and size of structures, and the seismicity of the area. The risk of structural damage is estimated considering three damage criteria: absolute and differential settlement, and the rotation of a structure. Liquefaction does not always lead to damage. Since a considerable amount of uncertainty is expected in the estimation of most of the parameters, a risk-based damage estimation procedure is suggested.
• Kanegaonkar, H. B., & Haldar, A. (1986). A response computation technique for offshore platform subjected to a class of non-normal stochastic loading.. Array, eds., Southampton, U.K., Comput. Mech. Publications, 1986, p.607-612..
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  Abstract: Proposes a hybrid method to study wave loading on offshore platforms. The method uses both spectral and probabilistic methods to calculate the first four moments of the response, considering the effects of nonlinearity of the wave kinematics and free surface fluctuations. Long term wave characteristics are represented by seven short term sea states. The exact values of the first and second moments are estimated using spectral analysis, and the third and fourth moments are estimated probabilistically. Presents the marginal distribution function used. Calculated deck deflections are given. (C.J.U.)
• Kanegaonkar, H. B., Haldar, A., & Ramesh, C. K. (1986). Fatigue analysis of offshore platforms with uncertainty in foundation conditions. Structural Safety, 3(2), 117-134.
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  Abstract: Foundation flexibility is an important consideration, in designing offshore structures against fatigue, since it has a significant effect on the system's dynamic response. However, a considerable amount of uncertainty is expected in the estimation of foundation flexibility due to the natural nonhomogeneity of the soil as well as laboratory and in-situ testing errors. The proposed method explicitly uses of the statistical nature of uncertainty in the soil stiffness to estimate the variability in the instanteneous and fatigue response using the First-Order Second Moment technique, with emphasis on uncertainties in the dynamic shear modulus along with random wave loading. Uncertainties in the response are estimated considering the randomness in the eigen values, eigen vectors, and the mechanical transfer function. Fatigue life is estimated at different levels of uncertainty for the dynamic shear modulus. It is observed that the uncertainty in the dynamic shear modulus of the soil has more significant effect on the fatigue life of the joints close to the base. The variability in the fatigue response increases with a reduction in the mean dynamic shear modulus. The response is more sensitive to changes in the dynamic shear modulus at its lower values. © 1986.
• Ayyub, B. M., & Haldar, A. (1985). DECISIONS IN CONSTRUCTION OPERATIONS.. Journal of Construction Engineering and Management, 111(4), 343-357.
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  Abstract: A method for selecting the most desirable construction strategy is proposed in this paper. A decision analysis framework is developed considering the information on relative risk, along with the information on cost, benefit, and consequences of each construction strategy. The risk of failure and cost of construction operations, and the consequences of failure need to be estimated in order to decide about the optimum construction strategy. The decision problem is complicated since the state of the factors are generally expressed in linguistic terms. The theory of fuzzy sets is used to translate these terms into mathematical measures and to estimate the risk of failure. The proposed method is illustrated with the help of an example.
• Ayyub, B. M., & Haldar, A. (1985). IMPROVED SIMULATION TECHNIQUES AS STRUCTURAL RELIABILITY MODELS.. Array, 17-26.
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  Abstract: The direct or Monte Carlo simulation method is inefficient in structural reliability analysis. This shortcoming can be overcome by using an appropriate variance reduction technique or a combination of several variance reduction techniques. The Conditional Expectation, Antithetic Variates, and Common Random Numbers variance reduction techniques are discussed in this paper along with several of their combinations. The combined Conditional Expectation plus Antithetic Variates variance reduction technique is found to be the most efficient structural reliability model in simulation.
• Haldar, A. (1985). ENERGY-BALANCED APPROACH TO EVALUATE LOCAL EFFECTS OF IMPACT OF NON DEFORMABLE MISSILES ON CONCRETE STRUCTURES.. Transactions of the International Conference on Structural Mechanics in Reactor Technology, J, 209-214.
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  Abstract: The energy-balanced approach is used in this study to evaluate the local effects of nondeformable missiles on concrete structures in terms of penetration depth. For nondeformable missiles, the kinetic energy of the missiles is dissipated into local strain energy in terms of penetration, back-face scabbing, or perforation, as well as overall structural response. This study confirms that the energy dissipation due to the overall structural response is very small compared to the local effects in most cases, and can be neglected. The energy-balanced approach is a viable alternative approach to estimate the penetration depth of nondeformable missiles striking concrete structures. The equations proposed in this paper can be used for this purpose. Once the penetration depth is known, the target thickness necessary to prevent back-face scabbing can be easily estimated.
• Haldar, A., & Chern, S. (1985). PROBABILISTIC PORE PRESSURE-INDUCED STRUCTURAL DAMAGE.. Array, 3. 3-3. 12.
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  Abstract: The generation and dissipation of pore water pressure in a saturated sand deposit during and following an earthquake dictates the type and extent of damage a site will experience. Most of the presently used methods are for a level ground surface. However, in practical problems, the soil elements along potential failure plane surfaces are subjected to an appreciable amount of static shear stresses. Thus, the behavior of such soil elements subjected to an earthquake is considerably different. The structural damage due to earthquake-induced liquefaction can be estimated in two parts: during and following an earthquake. In the first part, it is necessary to estimate the residual settlement during an earthquake due to the generation of pore water pressure. In the second part, it is necessary to evaluate the consolidation settlement following an earthquake due to the dissipation of pore water pressure.
• Haldar, A., & Chern, S. (1985). PROBABILISTIC STUDY ON STRUCTURAL DAMAGE DUE TO SETTLEMENT IN A LIQUEFIED SAND DEPOSIT.. Array, 3, 301-310.
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  Abstract: The most common types of damage that can be expected due to liquefaction are settlement, differential settlement, subsidence and tilting of a structure at the site. The damage criterion related to the differential settlement of foundation is especially addressed in this paper. In this work, a finite element model is developed for evaluating the general characteristics of pore water pressure build-up and dissipation in a saturated sand deposit during and following an earthquake motion. The differential settlement of footings is then determined by evaluating volume changes below the footings caused by pore water pressure dissipation. The influence on the damage assessment of uncertainties in the load and soil parameters is also discussed.
• Haldar, A., & Luettich, S. M. (1985). SUBSIDENCE APPROACH TO DAMAGE IN EARTHQUAKE-INDUCED LIQUEFACTION.. Array, 3. 13-3. 22.
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  Abstract: Earthquake-induced liquefaction causes damage to structures and property and is of major concern to engineers. To estimate damage during liquefaction, it is necessary to go one step beyond the evaluation of liquefaction potential. Damage is a highly controversial subject due to its qualitative nature. One extremely conservative limit case that is considered in this paper is liquefaction as a subsidence problem. This case could be visualized as the collapse of a tunnel in a soft deposit and its consequences. For a liquefaction problem this case can be modeled as a subsidence problem where all or part of the liquefied soil volume has flowed away from beneath the foundation, creating a void. Since a considerable number of parameters are involved in the problem and a considerable amount of uncertainty is expected in many of them, a risk-based damage estimation is essential. The development of such a model is the subject of this paper.
• Ayyub, B. M., & Haldar, A. (1984). PRACTICAL STRUCTURAL RELIABILITY TECHNIQUES.. Journal of Structural Engineering, 110(8), 1707-1724.
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  Abstract: Commonly-used structural reliability models are reviewed, and the advantages and limitations of each method are discussed with the help of a practical example. A pressure vessel is designed against wind loading. This example is selected because the limit state equation is nonlinear and the wind speed has an extremely skewed distribution. If simulation techniques, are used to study a problem, some kind of variance reduction technique should be used for economic reasons. For the complicated example considered here, the Conditional Expectation plus Antithetic Variates variance reduction technique is found to be the most efficient. The Monte Carlo Simulation technique is modified to make the simulation more efficient.
• Ayyub, B. M., & Haldar, A. (1984). PROJECT SCHEDULING USING FUZZY SET CONCEPTS.. Journal of Construction Engineering and Management, 110(2), 189-204.
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  Abstract: The uncertainty in the fuzzy relations can be modeled along with other sources of uncertainty. The mean and variance of the parameters involved in the problem under consideration are estimated using a new method. The method maximizes the product of the sum of the membership associations for a certain frequency of occurrence and the corresponding frequency of occurrence. One of the main advantages of the proposed technique is that it can be easily implemented in existing computer programs for project scheduling.
• Haldar, A. (1984). STATISTICAL SITE CHARACTERIZATION.. National Conference Publication - Institution of Engineers, Australia, 530-534.
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  Abstract: The estimation of parameters in any geomechanical problem is important and needs serious consideration. The predictability of the method depends on this often overlooked step, particularly when the parameters are estimated from the data from a few poorly sampled, widely spaced and often poorly logged borings. Methods are discussed here to model three-dimensional characteristics of a soil deposit statistically. A statistical site characterization model could complement a geomechanical problem.
• Haldar, A., & Ayyub, B. M. (1984). PRACTICAL VARIANCE REDUCTION TECHNIQUES IN SIMULATION.. American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 93, 63-74.
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  Abstract: The use of simulation techniques to estimate the risk or reliability of an engineering system are discussed. When simulation is used for a complicated engineering system, variance reduction techniques should be used for economic reasons For the complicated example considered here, the Conditional Expectation plus Antithetic Variates variance reduction technique is found to be the most efficient.
• Haldar, A., & Ayyub, B. M. (1984). RISK MODELS FOR CORRELATED NON-NORMAL VARIABLES.. Array, 2, 1237-1240.
• Haldar, A., & Hamieh, H. A. (1984). LOCAL EFFECT OF SOLID MISSILES ON CONCRETE STRUCTURES.. Journal of Structural Engineering, 110(5), 948-960.
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  Abstract: The appropriateness of the National Defense Research Council (NDRC) equations for penetration and back-face scabbing thicknesses are reevaluated using presently available test results. A nondimensional impact factor is introduced to improve the predictability of these equations. Penetration depths are estimated using NDRC, statistical NDRC, and the proposed Haldar equations. For most large turbine missiles, the scabbing thicknesses need to be estimated indirectly using the information on the penetration depth. The applicability of the proposed penetration and scabbing thicknesses to large turbine missiles such as those postulated by the General Electric Corp. and Westinghouse, are discussed. The coefficients of variation for the estimation of penetration and scabbing thicknesses are large in all cases. Thus, in any probabilistic formulation like the one used for turbine missiles, they should be considered probabilistically.
• Haldar, A., & Miller, F. J. (1984). STATISTICAL ESTIMATION OF RELATIVE DENSITY.. Journal of Geotechnical Engineering, 110(4), 525-530.
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  Abstract: A new relationship is proposed to estimate the in situ relative density indirectly from the information on the Standard Penetration Test values. The predictability of the proposed relationship is found to be better than the other commonly used relationships. However, the uncertainty associated with the prediction is considerable and needs to be considered in a probabilistic design.
• Haldar, A., & Miller, F. J. (1984). STATISTICAL EVALUATION OF CYCLIC STRENGTH OF SAND.. Journal of Geotechnical Engineering, 110(12), 1785-1802.
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  Abstract: A statistical model is proposed to estimate the cylic shear strength of a saturated sand deposit. Large-scale shaking table test results are used to develop the basic model since they reproduce the in situ test conditions more closely than other laboratory tests. Due to the unavialability of large-scale shaking table tests results for different soils and tests conditions, cyclic triaxial test results are used to modify this basic model. Factors affecting laboratory relationships that are considered in this study are methods of sample preparation, soil fabric, system compliance, mean grain size, multidirectionality of earthquake motions, and secondary factors. Factors affecting the in situ relationship are previous strain history, age, cementation, etc. It is observed that considerable uncertainty is expected in the estimation of the in situ cyclic shear strength. The uncertainty associated with the in situ relative density contributes significantly to the overall uncertainty.
• Haldar, A., & Ayyub, B. M. (1983). PRACTICAL PROBABILISTIC MODEL.. Array, 2, 948-951.
• Haldar, A., & Miller, F. J. (1983). DAMAGE IN LIQUEFACTION - A PROBABILISTIC MODEL.. Array, 332-340.
• Haldar, A., Hamieh, H. A., & Miller, F. J. (1983). PENETRATION AND SPALLATION DEPTH ESTIMATION FOR CONCRETE STRUCTURES.. Transactions of the International Conference on Structural Mechanics in Reactor Technology.
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  Abstract: The predictability of the National Defense Research Committee (NDRC) equations for penetration and spallation depth, particularly with respect to large solid missiles similar to those expected in a nuclear power plant, are reevaluated. Presently available test results for both solid missiles and bullets are used for this purpose. This study confirms the industry notion that the NDRC equations predict the penetration depth reasonably well for small missiles; however, they fail to do so for large missiles.
• Haldar, A. (1982). PROBABILISTIC EVALUATION OF WELDED STRUCTURES.. Journal of the Structural Division, 108(ST-9), 1943-1955.
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  Abstract: The paper outlines a probabilistic approach to account for the deficiency in welding, and suggests repair procedures where improvement is necessary.
• Haldar, A. (1982). STATISTICAL AND PROBABILISTIC METHODS IN GEOMECHANICS.. NATO Advanced Study Institutes Series, Series C: Mathematical and Physical Sciences, 92, 473-504.
• Haldar, A., & Miller, F. J. (1982). LOCAL EFFECTS EVALUATION OF CONCRETE STRUCTURES.. Array, 345-357.
• Haldar, A., & Miller, F. J. (1982). PROBABILISTIC EVALUATION OF LIQUEFACTION IN A 3-D SOIL DEPOSIT.. Array, 2, 607-617.
• Haldar, A., & Miller, F. J. (1982). Penetration depth in concrete for nondeformable missiles. Nuclear Engineering and Design, 71(1), 79-88.
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  Abstract: The ability of the NDRC equations to estimate the penetration depth in concrete structures has been reevaluated using the presently available test results. This study confirms the industry notion that the NDRC equations overpredict the penetration depth. The NDRC equations, when used with a safety factor, can give a penetration depth about two standard deviations away from the mean value. In a probabilistic formulation the use of this penetration depth is over-conservative and unrealistic. The NDRC equation is updated here statistically using the presently available test results. This statistical NDRC equation significantly improves the predicted penetration depth. However, the form of the NDRC equation may not be ideal. A new relationship is proposed here to estimate the penetration depth by introducing a dimensionless impact factor. It has been shown here that the proposed relationship is better than the NDRC or even the statistical NDRC equations. © 1982.
• Haldar, A., & Miller, F. J. (1982). Probabilistic evaluation of damage potential in earthquake- induced liquefaction in a 3-D soil deposit.. Array.
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  Abstract: A detailed statistical evaluation of the soil parameters in the proposed liquefaction model is provided and the uncertainty associated with the estimation of in situ relative density is evaluated for both direct and indirect methods. In the evaluation of the liquefaction potential of a site, it was found that the uncertainties in the load parameters could be higher than those in the resistance parameters.-from US Govt Reports Announcements, 17, 1982
• Haldar, A., & Miller, F. J. (1982). Probabilistic evaluation of liquefaction in a 3-D soil deposit.. Soil dynamics and earthquake engineering. Proc. conference, Southampton, July 1982. Vol. 2, 607-617.
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  Abstract: This study systematically identifies all the appropriate parameters affecting the liquefaction potential of a saturated soil deposit during an earthquake, and evaluates the uncertainties therein. The objective is to develop a simple but practical and efficient probabilistic method which will estimate the risk of liquefaction in three dimensions. -from Authors
• Haldar, A. (1981). PROBABILISTIC EVALUATION OF CONSTRUCTION DEFICIENCIES. Journal of the Construction Division, 107(1), 107-119.
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  Abstract: A probabilistic procedure is formulated to evaluate construction deficiencies involving hundreds of identical structural elements in which uniformity of quality is desirable. These include welds in truss systems, pipe hanger systems, and shear studs in reinforced concrete structures to develop composite strength. A deterministic solution to this type of problem may be inadequate, as may a simple binomial distribution. The use of the hyperbinomial distribution is most appropriate since the success rate parameter is a random variable. The distribution also shows how added information could help make a better decision. The procedure is discussed using shear studs in reinforce concrete structures as an example. Some repair procedures are also suggested. This method may be a safe and economical way to deal with some construction deficiency problems.
• Haldar, A., & Tang, W. H. (1981). STATISTICAL STUDY OF UNIFORM CYCLES IN EARTHQUAKES. Journal of the Geotechnical Engineering Division, 107(5), 577-589.
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  Abstract: The applicability of equivalent uniform stress cycles in soil dynamics to the study of soil behavior during and after an earthquake is explored. The actual irregular time histories produced by an earthquake can be represented by uniform amplitude cyclic stresses, although there may be a considerable amount of uncertainty associated with them. The stress level of 75 percent of the maximum is suggested for such conversion, since in this case the uncertainty in the normalized soil-strength curve has a minimum effect on the value of the N//S//e//q versus M relationship. A statistical relationship between N//S//e//q and the earthquake magnitude is proposed here based on results available in the literature. The N//S//e//q could be estimated adequately by considering the component of excitation containing the peak acceleration. The N//S//e//q versus M relationship proposed is somewhat different from the relationship suggested by Seed and Idriss. This discrepancy in N//S//e//q values may not yield significant differences in estimating the soil strength in a liquefaction study.
• Haldar, A. (1980). LIQUEFACTION STUDY - A DECISION ANALYSIS FRAMEWORK. Journal of the Geotechnical Engineering Division, 106(12), 1297-1312.
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  Abstract: A decision analysis framework is developed here to study the liquefaction problem. When the liquefaction risk of a site is found to be unacceptable, several alternatives could be attempted. However, economic as well as technical aspects need to be considerd in selecting the best solution. This type of study would be particularly helpful if the limitation or elimination of damage associated with liquefaction is a design criterion. In this paper, several design alternatives for a liquefaction study have been identified and a decision tree is used to organize essential information. A decision can be made with available information or with additional information if additional time and money are available. Collection of additional information may not be always desirable for all projects. It depends on many factors and they are identified here. If the additional information is disirable, the maximum amount of money that should be spent can also be estimated from this study.
• Haldar, A. (1979). Turbine missile - a critical review. Nuclear Engineering and Design, 55(3), 293-304.
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  Abstract: The turbine missile problem has been critically reviewed. A probabilistic approach to the problem seems to be most reasonable. However, United States Nuclear Regulatory Commission's guidelines on this subject may not be adequate. In this paper, some of the critical parameters in the turbine missile problem have been identified and their probabilistic characteristics have been discussed. Separation of high and low trajectory missiles in damage potential evaluation appears to be inappropriate. Definitions of targets from the engineer's point of view have also been suggested. In estimating the occurrence rate of external missiles the statistical approach using the Duane growth rate model seems to be more appealing than the systems reliability approach. However, the observed samples and durations may not be adequate for the Duane growth rate model. A probabilistic methodology to estimate the damage potential of turbine missiles is also developed considering various sources of uncertainty. The methodology is clarified with the help of an example. If the uncertainties in the contributing parameters are considered appropriately, the crude conservatism that has been introduced into the damage potential evaluation can be reduced with confidence. © 1979.
• Haldar, A., & Tang, W. H. (1979). PROBABILISTIC EVALUATION OF LIQUEFACTION POTENTIAL. ASCE J Geotech Eng Div, 105(2), 145-163.
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  Abstract: A procedure for predicting probability of liquefaction is used to estimate the probability of liquefaction for a given design earthquake magnitude and acceleration or when the earthquake loading is considered as random. Reasonable comparison is obtained between the probabilities computed and the field observations of liquefaction occurrences. Uncertainty analysis of the Seed and Idriss simplified method reveals that the uncertainties in the load parameters exceed those in the resistance parameters. Thus, the seismic activity of the region should be given serious consideration, as well as the attenuation characteristics. When the maximum acceleration and earthquake magnitude are specified, the probability of liquefaction will be governed by the uncertainties in the relative density and cyclic shear strength parameters. As an alternative tool of analysis the probabilistic model could complement the deterministic procedures by providing information on the relative risk of liquefaction between design alternatives.
• Haldar, A. (1978). PROBABILISTIC EVALUATION OF TURBINE MISSILE DAMAGE POTENTIAL.. Welding in the World, Le Soudage Dans Le Monde, 1-20.
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  Abstract: The generation and consequences of turbine missiles have been getting considerable attention recently in the nuclear industry. The fracture mechanism of the turbine wheel and the physical processes of those missiles damaging safety-related structures are extremely complicated in a deterministic sense. In this paper, an overall evaluation of the turbine missile problem is made. The complexities in separating high and low trajectory missiles and the damage potential associated with them when applied to a real nuclear power plant is discussed in detail with the help of examples. A detailed discussion is made on the parameters commonly known in the industry as P//1, P//2, P//3, and P//4. A statistical evaluation of the parameter P//1 is made. Some of the important aspects that need to be considered in the calculation of P//2 are considered. Moreover, the damage criteria, namely, spallation or back face scabbing, penetration, and perforation and the influence of using different equations (NDRC, BRL, etc. ) with their associated variabilities in the calculation of P//3 are discussed. Finally, a probabilistic methodology is developed for the calculation of the P//4-value considering high speed and normal speed failure, and the number and the locations of the wheels in an LP turbine unit, for the whole power plant.

Proceedings Publications

• Haldar, A. (2019, January). Keynote lecture - Uncertainty Modeling for Nonlinear Dynamic Systems - Loadings Applied in Time Domain. In International Conference on Reliability Safety and Hazard (ICRESH-2019), Indian Institute of Technology, Madras, Chennai, India.
• Haldar, A., Gaxiola-Camacho, J. R., Azizsoltani, H., Villegas-Mercado, F. J., & Vazirizade, S. M. (2019, 03). Keynote lecture - A Novel Geomechanics Concept for Earthquake Excitations Applied in Time Domain. In The International Association for Computer Methods and Advances in Geomechanics (IACMAG), 18.
• Villegas-Mercado, F. J., Haldar, A., Gaxiola-Camacho, J. R., & Vazirizade, S. M. (2019, Fall). Structural Reliability Assessment of Moment Resisting Frames and Concentrically Braced Frames with Partially Restrained Connections. In XXII National Congress of Seismic Engineers, Mexico.
• Haldar, A. (2018, 09). Keynote Lecture - Structural health assessment: Past, Present, and Future. In The 8th International Workshop on Structural Life Management of Eco-Power Structures, Korea Electric Power Corporation Research Institute (KEPCO-RI), Daejeon, Korea, 15-22.
• Al-Hussein, A. .., & Haldar, A. (2017). Quality and Quantity of Measured Information in Structural Health Monitoring. In 12th International Conference on Structural Safety and Reliability (ICOSSAR'17).
• Azizsoltani, H., & Haldar, A. (2017). A Surrogate Concept of Multiple Deterministic Analyses of Non-linear Structures Excited by Dynamic Loadings. In 12th International Conference On Structural Safety And Reliability (ICOSSAR'17).
• Gaxiola-Camacho, J. R., Haldar, A., Villegas-Mercado, F. J., & Reyes-Salazar, A. .. (2017). Performance-Based Seismic Design Uing An Integrated Structural Reliability Evaluation Approach. In 16th World Conference on Earthquake Engineering.
• Haldar, A. (2017). Keynote Lecture - Design of Seismic Damage Tolerant Steel Structures. In 3rd Euro Congress on Steel and Steel Structures, London, U.K..
• Haldar, A. (2017, November). Keynote lecture - Future of Structural Safety and Reliability Assessment. In Taishan Academic Forum on Structural Safety and Reliability Assessment, Shandong University, China.
• Azizsoltani, H., Sen, N., & Haldar, A. (2016). Reliability Evaluation of Large Nonlinear Structures Excited by Dynamic Loadings Applied in Time Domain. In EMI/PMC 2016, ASCE.
• Haldar, A. (2016). Keynote Lecture - Structural Health Monitoring: Past, Present and Future. In Engineering Mechanics Institute and Probabilistic Mechanics and Reliability Conference, ASCE.
• Sen, N., Azizsoltani, H., & Haldar, A. (2016, May). Issues in Generating Response Surfaces for Reliability Analysis of Large Complex Dynamic Systems. In EMI/PMC 2016, ASCE.
• Al-Hussein, A. .., & Haldar, A. (2015). A Comparison of Unscented and Extended Kalman Filtering for Nonlinear System Identification. In 12th International Conference on Applications of Statistics and Probability in Civil Engineering, (ICASP12), Vancouver, Canada,.
• Al-Hussein, A. .., & Haldar, A. (2015). Computational Intelligence for Structural Identifications. In IEEE Symposium Series on Computational Intelligence (IEEE SSCI 2015), Cape Town, South Africa.
• Haldar, A., & Al-Hussein, A. .. (2015). Keynote - Prognostics and Structuring Health Assessment Using Uncertain Measured Response Information. In International Conference on Reliability, Safety, and Hazard (ICRESH) and Advances in Reliability, Maintenance, and Safety (ARMS).
• Haldar, A., & Al-Hussein, A. (2014, Jan.). Structural Health Assessment: Challenges - Inaugural Keynote Paper. In International Conference on Disaster Mitigation, ICDM’14, K7-1 to K7-10.
• Haldar, A., & Al-Hussein, A. (2014, March). A new extension of unscented Kalman filter for structural health assessment with unknown input. In SPIE Smart Structures/NDE 2014.
• Al-Hussein, A., Das, A. K., & Haldar, A. (2013, January). A new approach for structural health assessment using unscented kalman filter. In Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures - Proceedings of the 11th International Conference on Structural Safety and Reliability, ICOSSAR 2013 (Referred), 1579-1585.
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  Abstract: Atime-domain System Identification (SI)-based Structural Health Assessment (SHA) procedure using Extended Kalman Filter (EKF) concept is presented in another paper. Unscented Kalman Filter (UKF) concept is presented in this paper. Both procedures can be used to assess health of existing or newly built structures exhibiting nonlinear behavior. To apply these procedures, the structures are represented by finite elements. The locations and the rates of degradation of the elements are tracked to assess the structural health. Both EKF and UKF-based formulations are expected to assess health for nonlinear structures. Since the mathematical formulations are different, their application potentials to identify health of structures with different types of nonlinearities are expected to be different. The most important attribute of the UKF-based procedure is that it will not require the linearization of nonlinear responses as required by the EKF-based procedure.A comparative study of the two procedures is presented in this paper. It is shown that one method may be superior to the other to assess structural health in the presence of different defect scenarios and associated nonlinearities. © 2013 Taylor & Francis Group, London.
• Al-Hussein, A., Das, A. K., & Haldar, A. (2013, June). Algorithmic and Computing Technologies for Health Assessment of Real Structures in the Presence of Large Nonlinearity. In 2013 ASCE International Workshop on Computing in Civil Engineering.
• Das, A. K., & Haldar, A. (2013, January). Improvements in the kalman filter concept for structural health assessment. In Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures - Proceedings of the 11th International Conference on Structural Safety and Reliability, ICOSSAR 2013 (Referred), 1587-1592.
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  Abstract: Health assessment of existing structural systems has developed multi-disciplinary research interests in the recent past. The research team at the University of Arizona is in the process of developing several finite elements (FE)-based system identification (SI) procedures that provide information on the location(s) of defect(s) and their severity by tracking the signature embedded in the dynamic responses. The procedures do not require information on input excitation. To address the issue related to measured noise-contaminated acceleration time-histories at limited DDOFs in large structural systems, the team developed integrated procedures by improving the extended Kalman Filter (EKF) concept. However, during the development phase, the team needed to address several fundamental challenges. Appropriate offline signal processing schemes, including filtering, baseline removal, and mitigation of amplitude and phase-shift errors, etc. needed to be introduced to address the issues of non-convergence. They are discussed in this paper. © 2013 Taylor & Francis Group, London.
• Das, A. K., Al-Hussein, A., & Haldar, A. (2013, January). Algorithmic and computing technologies for health assessment of real structures in the presence of nonlinearity and uncertainty. In Computing in Civil Engineering - Proceedings of the 2013 ASCE International Workshop on Computing in Civil Engineering, 49-56.
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  Abstract: The research team at the University of Arizona proposed several novel structural health assessment (SHA) algorithms. Structures are represented by finite elements (FE) and the health is assessed by identifying the stiffness parameters of all the elements and comparing them with expected values or with previous values, or by observing differences between similar elements. They can identify the location and severity of defect and exact location within a defective element. These algorithms use several system identification- (SI-) based concepts with different levels of sophistications. They do not require excitation information and can assess the health of large structural systems using only limited noise-contaminated acceleration time-histories measured at a small part of a structure. They are widely available in the literature. However, algorithmic and computational rigors of them are generally not presented in technical papers due to severe page limitation. Some of them are briefly presented in this paper without discussing the specific algorithms. © 2013 American Society of Civil Engineers.
• Haldar, A., Farag, R., & Huh, J. (2013, January). Challenges in the reliability analysis of large dynamic systems - A novel approach. In Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures - Proceedings of the 11th International Conference on Structural Safety and Reliability, ICOSSAR 2013 (Referred), 2859-2866.
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  Abstract: There is a vacuum in the reliability analysis procedures for large structural systems. The risk analysis procedures should explicitly satisfy all major sources of nonlinearity expected just before failure and the associated uncertainties. One can argue that simulation-based formulations can always be used in the absence of any such procedure. The authors observed that one deterministic nonlinear finite element-based realistic analysis of large systems may take over 5 hours of continuous running of a computer. For the risk analysis of the order of 10-3, at least 10,000 simulations will be required. Thus, it may take years of continuous running of a computer, and yet the extracted probability of failure information may not be representative. The research team is now in the process of developing and verifying a hybrid approach consisting of nonlinear stochastic finite element method, the first/second-order reliability method, response surface method, and advanced factorial schemes. This hybrid approach will be presented in the paper. © 2013 Taylor & Francis Group, London.
• Ramos, C. P., & Haldar, A. (2013, January). Three-dimensional response of reinforced concrete bridges under spatially varying seismic excitation. In Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures - Proceedings of the 11th International Conference on Structural Safety and Reliability, ICOSSAR 2013 (Referred), 1169-1175.
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  Abstract: A novel approach to study nonlinear seismic response behavior of three-dimensional (3-D) concrete bridges is presented in a six step methodology. The methodology rigorously considers spatial variability in the seismic excitation (SVSE) caused by wave passage and incoherence and local soil conditions, as well as the effects of far-field and near-field epicentral distance. Bridges are represented by 3-D finite element models with bidirectional plastic hinges at piers and soil-foundation interface elements that account for soil dynamic stiffness at each ground support. Results on pier rotational Ductility Demands (DD) in symmetric and asymmetric multi-span bridges considered in the study indicate that the magnitude of the DD depends on the type of soil, the pier location and the length of the bridge. Results also show that ignoring SVSE effects can cause severe underestimation of DD. © 2013 Taylor & Francis Group, London.
• Reyes-Salazar, A., Bojórquez, E., Rivera-Salas, J. L., Velazquez-Dimas, J. I., & Haldar, A. (2013, September). Ductility Reduction Factors For Steel Buildings With Perimeter Moment Resisting Frames. In Fifth International Conference on Structural Engineering, Mechanics and Computation(SEMC-2013), South Africa.
• Reyes-Salazar, A., Rodelo-López, R. E., Bojórquez, E., Rivera-Salas, J. L., Velazquez-Dimas, J. I., & Haldar, A. (2013, September). Relative effect of damping and yielding on the seismic response of 3D steel buildings with perimeter moment resisting frames. In The 2013 World Congress on Advances in Structural Engineering and Mechanics (ASEM 2013), Korea.
• Das, A. K., & Haldar, A. (2012, Summer). Health Prognosis of Large Engineering Structures using Minimum Information. In 2012 Joint Conference of the Engineering Mechanics Institute and the 11th ASCE Joint Specialty Conference on Probabilistic Mechanics and Structural Reliability.
• Haldar, A. (2012, January). Past, Present, and Future of Engineering under Uncertainty: Safety Assessment and Management - Inaugural Keynote paper. In International Symposium on Engineering under Uncertainty: Safety Assessment and Management, ISEUSAM-2012, India.
• Haldar, A., & Das, A. K. (2012, January). Health Assessment of Structures – Past, Present, and Future - Invited paper. In International Symposium on Engineering under Uncertainty: Safety Assessment and Management, ISEUSAM-2012, India.
• Haldar, A., & Farag, R. (2012, Summer). Reliability Evaluation of Laterally Loaded Deep Foundation. In Fifth Asian-Pacific Symposium on Structural Reliability and its Applications (5APSSRA), Wilson Tang’s Memorial Lecture.
• Huh, J., Farag, R., & Haldar, A. (2012, Summer). A Reliability Evaluation Method for Performance-Based Design. In 2012 Joint Conference of the Engineering Mechanics Institute and the 11th ASCE Joint Specialty Conference on Probabilistic Mechanics and Structural Reliability.
• Reyes-Salazar Rivera-Leyva J.O., Haldar A., De Leon-Escobedo D. and López-López D., A., Rivera-Leyva De Leon-Escobedo D. and López-López D., J. O., Haldar, A., De Leon-Escobedo, D., & López-López, D. (2012, September). Ductility, Interstory Shear and Displacements Demands of Steel Buildings with Perimeter and Spatial Moment Resisting Frames, Paper No. 2379. In 15th Word Conference on Earthquake Engineering (15WCEE).

Others

• Haldar, A., & Ahlers, B. J. (2020, April). Structural Health Assessment Using System Identification Techniques in the Time and Frequency Domain. University of Arizona.
• Haldar, A., & • Vazirizade, S. M. (2019, December). An intelligent Integrated Method for Reliability Estimation of offshore structures Wave Loading Applied in Time Domain. University of Arizona.
• Azizsoltani, H., & Haldar, A. (2017, Spring, 2017). Risk Estimation Of Nonlinear Time Domain Dynamic Analyses Of Large Systems. University of Arizona.
• Gaxiola, C., & Haldar, A. (2017, Spring, 2017). Performance-Based Seismic Design Of Nonlinear Steel Structures Using A Novel Reliability Technique. University of Arizona.
• McGuire, M., & Haldar, A. (2017, April). Vibration Data Collection and Analysis for Industrial Applications. University of Arizona.
• Aonyas, S., & Haldar, A. (2016, Fall). Case Study of Performance Based Seismic Design Approach of a Special Moment Frame. University of Arizona.
• Maciosek, J., & Haldar, A. (2016, December). Analysis and Mitigation of Vortex-Induced Vibrations in Overhead Transmission Line Conductors. University of Arizona.
• Al-Hussein, A. .., & Haldar, A. (2015, August). A Novel Technique for Structural Health Assessment in the Presence of Nonlinearity. University of Arizona.
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  University of Arizona
• Camacho, J., & Haldar, A. (2015, Spring). Structural Reliability of Steel Moment Resisting Frames using Performance Based Seismic Design/Analysis Concept. University of Arizona.
• Haldar, A. (2014, Jan). Disaster Mitigation - Special Plenary Lecture as the Guest of Honor. International Conference on Disaster Mitigation, ICDM’14.
• Haldar, A. (2014, Spring). Inaugural Keynote paper - Engineering Computations of Large Infrastructures in the Presence of Uncertainty. 6th International Workshop on Reliable Engineering Computing – Reliability and Computations of Infrastructures,pp. 96-115.
• Hartke, N., & Haldar, A. (2014, May). Flexural Strength on Post-Tensioned, Concrete-Filled, Tubular-Flanged Girders. University of Arizona.
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  Based on M.S. report of Mr. Hartke.
• Milligan, J., & Haldar, A. (2014, May). Structural Design of Thermal Mass. University of Arizona.
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  Based on the M.S. report of Mr. Milligan.
• Haldar, A., & Sedgeman, A. (2013, May). America’s Current Infrastructure and Health Assessment of Bridges. University of Arizona.
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  Based of M.S. report of Mr. Sedgeman.
• Rey, A. I., & Haldar, A. (2013, May). Determination of Axial Strength Resistance Factors for Drilled Shafts in Arizona Soils using AASHTO Beta Method. University of Arizona.
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  Based on the M.S. report of Mr. Rey.
• Das, A. K., & Haldar, A. (2012, December). Health Assessment of Three Dimensional Large Structural Systems Using Limited Uncertain Dynamic Response Information. University of Arizona.
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  Based on the Ph.D. Dissertation of Dr. Das.
• Haldar, A., & Mahadevan, S. (2000). Probability, reliability, and statistical methods in engineering design.