Hamid Saadatmanesh

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• Toufigh, V., Saeid, F., Toufigh, V., Ouria, A., Desai, C. S., & Saadatmanesh, H. (2013). Laboratory study of soil-CFRP interaction using pull-out test. Geomechanics and Geoengineering.
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  Abstract: Soil is a material which is weak in tension; however, different materials such as geotextiles are used to address this inadequacy. In recent years more than one million square metres of geotextiles were used for reinforcing soil. Nevertheless, there are several significant problems associated with geotextiles, such as creep, low modulus of elasticity and susceptibility to aggressive environments. Carbon fibre reinforced polymer (CFRP) was introduced over two decades ago to the field of structural engineering and it can also be used in geotechnical engineering. CFRP has all the benefits associated with geotextiles and it boasts a higher strength, higher modulus, no creep and reliability in aggressive environments. In this investigation, the interface properties of CFRP-sand and fine sand were investigated using the pull-out test. The pull-out test device was designed and assembled using a triaxial loading device and a direct shear device. In the pull-out test, the normal force applied by the triaxial loading and pull-out force is applied by a direct shear device. CFRP samples were prepared in the lab. Precast and cast-in-place samples were tested. The pull-out force and corresponding displacements of each of the materials were recorded and compared. © 2013 Copyright Taylor and Francis Group, LLC.
• Toufigh, V., Toufigh, V., & Saadatmanesh, H. (2013). Behavior of FRP bonded to steel under freeze thaw cycles. Steel and Composite Structures, 14(1), 41-55.
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  Abstract: Fiber reinforced polymers (FRP) materials are increasingly being used for strengthening and repair of steel structures. An issue that concerns engineers in steel members which are retrofitted with FRP is stress experienced due to temperature changes. The changing temperature affects the interface bond between the FRP and Steel. This research focused on the effects of cyclical thermal loadings on the interface properties of FRP bounded to steel members. Over fifty tests were conducted to investigate the thermal effects on bonding between FRP and steel, which were cycled from temperature of -11°C (12°F) to 60°C (140°F) for 21-36 days. This investigation consisted of two test protocols, 1) the tensile test of epoxy resin, tack coat, FRP and FRP-steel plate, 2) tensile test of each FRP compound and FRP with steel after going through thermal cyclic loading. This investigation reveals an extensive reduction in the composite's strength.
• Saadatmanesh, H., Tavakkolizadeh, M., & Mostofinejad, D. (2010). Environmental effects on mechanical properties of wet lay-up fiber-reinforced polymer. ACI Materials Journal, 107(3), 267-274.
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  Abstract: The demand for fiber-reinforced polymers (FRPs) in rehabilitation of infrastructure is increasing. New techniques use the light weight, high strength, and formability of FRP fabrics and laminates in various concrete retrofitting projects. This paper presents the results of studies on the long-term behavior of different types of FRP laminates produced using the wet lay-up technique. This technique is the most used infield application of FRPs on concrete structures. The scope of the paper is limited to only one mode of failure: laminate failure. It is noted that another form of failure is the bond at the interface. This mode of failure is currently under investigation at the University of Arizona. A total of 525 specimens were prepared using one type of epoxy and seven different types of fabrics. Unidirectional and bidirectional fabrics made from glass, carbon, and aramid were used in this study. The samples were exposed to nine different environments. These environments were simulated using four different chemical solutions with a pH of 12.5, 10, 7, and 2.5 and substitute seawater. Additional FRP samples were exposed to ultraviolet (UV) radiation, temperatures of 60 and 50°C (140 and 122°F) with 95% relative humidity (RH), and soil with 25% moisture content and active microorganisms in specially constructed chambers. Uniaxial tension tests were performed on the samples after 6000, 12,000, and 20,000 hours of exposure as well as on control samples; and tensile properties were measured for each specimen. The results showed a significant loss of strength and ultimate strain for glass FRP (GFRP), especially in environments with high pH values, while carbon and hybrid glass-carbon laminates showed very little loss of mechanical properties. Copyright © 2010, American Concrete Institute. All rights reserved.
• Woods, J. M., Kiousis, P. D., Ehsani, M. R., Saadatmanesh, H., & Fritz, W. (2007). Bending ductility of rectangular high strength concrete columns. Engineering Structures, 29(8), 1783-1790.
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  Abstract: A study was conducted on eight high strength concrete columns (fc′ = 69 MPa) with dimensions 203×203×2030 mm. The intent of the study was to isolate the effects of the spacing and volumetric content of the transverse reinforcement on the bending ductility of high strength concrete columns. To this end, four of the columns were reinforced with ties of constant spacing (76 mm) but different diameter (3.2, 4.8, 6.4, and 8.0 mm), while the other four columns were reinforced with ties of different spacing but constant volumetric content (1.1%). Clear trends in the effects of the volumetric content and spacing of the transverse reinforcement were observed within a range of values outside of which the effects were minimal. © 2006 Elsevier Ltd. All rights reserved.
• Buell, T. W., & Saadatmanesh, H. (2005). Strengthening timber bridge beams using carbon fiber. Journal of Structural Engineering, 131(1), 173-187.
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  Abstract: This research project demonstrates how advanced composite materials can be used to strengthen existing timber bridge beams in order to increase the load capacity of the bridge. Many times, the timber bridges were not designed to withstand the heavy truck traffic that they are currently carrying, and are therefore replaced in favor of modern concrete or steel bridges. Current methods of strengthening timber bridges are not always practical or economical and so these bridges are simply replaced at a high cost to the public. This project investigated whether applying composites in the form of either a fabric wrap or laminate strips to timber beams would increase the load capacity of the beams. Bidirectional carbon fabric was the primary strengthening material used. A total of 10 solid-sawn Douglas Fir timber beams were taken from a timber stringer bridge in Yuma, Ariz. that was replaced in 1999. Seven of the 10 creosote-treated beams were reinforced with carbon fiber and then tested for bending strength, shear strength, and stiffness. Three of the beams were tested as unreinforced control specimens. The results show that applying carbon fabric to the timber beams provides significant increases in the bending and shear capacity, and nominal increases in the stiffness of the beams. Allowable stress modification factors are conceptually discussed that could potentially be used by engineers to determine the safe load-carrying capacity of beams reinforced with carbon fiber. However, a statistically significant number of timber beams strengthened with carbon fiber need to be tested to arrive at definitive stress modification factors.
• Tang, T., & Saadatmanesh, H. (2005). Analytical and experimental studies of fiber-reinforced polymer-strengthened concrete beams under impact loading. ACI Structural Journal, 102(1), 139-149.
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  Abstract: A series of 27 concrete beams were tested to investigate the behavior of beams strengthened with fiber-reinforced polymer (FRP) laminates under impact loading. Two out of the 27 beams were not retrofitted and were used as control specimens. The impact force was delivered with a steel cylinder drop weight. The test results revealed that bonding composite laminates to concrete beams could significantly improve the performance of this type of structure to resist impact loading. In addition, bonding laminates increased cracking and flexural strength, as well as residual stiffness of the beams. Furthermore, it reduced the number of cracks, crack widths, and the maximum deflection. The residual stiffness of the strengthened beam after first impact was two to three times that of an unretrofitted beam, and the maximum deflection decreased by 30 to 40%. The improvement depends on the type and weight of composite laminate. compared with the static test results, the ultimate deflection, number of cracks, and crack width were smaller, but the maximum reaction force was three to four times larger than those of the beam under static loading. The residual stiffness of the strengthened beam after first impact can be calculated using a regression equation. The impact force can be obtained with a semi-empirical equation, which is derived from Spring-Mass models and modified by the test results. From flexural wave theory, an equation has been developed for predicting the deflection of a beam caused by impact loading. Copyright © 2005, American Concrete Institute.
• Tang, T., & Saadatmanesh, H. (2003). Behavior of concrete beams strengthened with fiber-reinforced polymer laminates under impact loading. Journal of Composites for Construction, 7(3), 209-218.
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  Abstract: Most of the research on application of composite materials in civil engineering during the past decade has concentrated on the behavior of structural elements under static loads. In engineering practice, there are many situations in which structures undergo impact or dynamic loading. In particular, the impact response of concrete beams strengthened with composite materials is of interest. This paper presents the results of an experimental investigation conducted to study the impact effects on concrete beams strengthened with fiber-reinforced polymer laminates. Two types of composite laminates, carbon and Kevlar, were bonded to the top and bottom faces of concrete beams with epoxy. Five beams were tested: two strengthened with Kevlar laminates, two strengthened with carbon laminates, and one unretrofitted beam as the control specimen. The impact load was applied by dropping a steel cylinder from a specified height onto the top face of the beam. The test results revealed that composite laminates significantly increased the capacity of the concrete beams to resist impact load. In addition, the laminates reduced the deflection and crack width. Comparing the test results of the beams strengthened with Kevlar and carbon laminates indicated that the gain in strength depends on the type, thickness, weight, and material properties of the composite laminate.
• Tavakkolizadeh, M., & Saadatmanesh, H. (2003). Fatigue strength of steel girders strengthened with carbon fiber reinforced polymer patch. Journal of Structural Engineering, 129(2), 186-196.
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  Abstract: Fatigue sensitive details in aging steel girders is one of the common problems that structural engineers are facing today. The design characteristics of steel members can be enhanced significantly by epoxy bonding carbon fiber reinforced polymers (CFRP) laminates to the critically stressed tension areas. This paper presents the results of a study on the retrofitting of notched steel beams with CFRP patches for medium cycle fatigue loading (R = 0.1). A total of 21 specimens made of S127×4.5 A36 steel beams were prepared and tested. Unretrofitted beams were also tested as control specimens. The steel beams were tested under four point bending with the loading rate of between 5 and 10 Hz. Different constant stress ranges between 69 and 379 MPa were considered. The length and thickness of the patch were kept the same for all the retrofitted specimens. In addition to the number of cycles to failure, changes in the stiffness and crack initiation and growth were monitored during each experiment. The results showed that the CFRP patch not only tends to extend the fatigue life of a detail more than three times, but also decreases the crack growth rate significantly.
• Tavakkolizadeh, M., & Saadatmanesh, H. (2003). Repair of damaged steel-concrete composite girders using carbon fiber-reinforced polymer sheets. Journal of Composites for Construction, 7(4), 311-322.
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  Abstract: The aging infrastructure of the United States requires significant attention for developing new materials and techniques to effectively and economically revive this aging system. Damaged steel-concrete composite girders can be repaired and retrofitted by epoxy bonding carbon fiber-reinforced polymer (CFRP) laminates to the critical areas of tension flanges. This paper presents the results of a study on the behavior of damaged steel-concrete composite girders repaired with CFRP sheets under static loading. A total of three large-scale composite girders made of W355×13.6 A36 steel sections and 75-mm-thick by 910-mm-wide concrete slabs were prepared and tested. One, three, and five layers of CFRP sheet were used to repair the specimen with 25, 50, and 100% loss of the cross-sectional area of their tension flange, respectively. The test results showed that epoxy bonded CFRP sheet could restore the ultimate load-carrying capacity and stiffness of damaged steel-concrete composite girders. Comparison of the experimental and analytical results revealed that the traditional methods of analysis of composite beams were conservative.
• Tavakkolizadeh, M., & Saadatmanesh, H. (2003). Strengthening of steel-concrete composite girders using carbon fiber reinforced polymers sheets. Journal of Structural Engineering, 129(1), 30-40.
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  Abstract: The use of advanced composite materials for rehabilitation of deteriorating infrastructure has been embraced worldwide. The conventional techniques for strengthening of substandard bridges are costly, time consuming, and labor intensive. Many new techniques have used the lightweight, high strength, and the corrosion resistance of fiber reinforced polymers (FRP) laminates for repair and retrofit applications. The load-carrying capacity of a steel-concrete composite girder can be improved significantly by epoxy bonding carbon fiber reinforced polymers (CFRP) laminates to its tension flange. This paper presents the results of a study on the behavior of steel-concrete composite girders strengthened with CFRP sheets under static loading. A total of three large-scale composite girders made of W355×13.6 A36 steel beam and 75-mm thick by 910-mm wide concrete slab were prepared and tested. The thickness of the CFRP sheet was constant and a different number of layers of 1, 3, and 5 were used in the specimens. The test results showed that epoxy-bonded CFRP sheet increased the ultimate load-carrying capacity of steel-concrete composite girders and the behavior can be conservatively predicted by traditional methods.
• Mei, H., Kiousis, P. D., Ehsani, M. R., & Saadatmanesh, H. (2001). Confinement effects on high-strength concrete. ACI Structural Journal, 98(4), 548-553.
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  Abstract: An experimental investigation was conducted on the stress-strain characteristics of steel sleeve confined high-strength concrete (HSC). The axial load and strains of concrete, and the axial and hoop strains of the confining steel sleeves were measured. From these measurements, accurate stress-strain relations of the concrete core were produced, along with confinement calculations based on von-Mises elastoplastic response of the steel sleeves. Confinements ranging from 5 to 19 MPa were calculated. This confinement had a profound effect on the strength of concrete, as much as tripling its unconfined strength of 70 MPa. The increase in ductility was found to develop slower for low amounts of confining steel due to a lagging development of confining pressure. This was attributed to the reduced tendencies of HSC to exhibit lateral expansion and the early yielding of the sleeve hoop stresses due to the biaxial nature of stresses within the sleeves.
• Tavakkolizadeh, M., & Saadatmanesh, H. (2001). Galvanic corrosion of carbon and steel in aggressive environments. Journal of Composites for Construction, 5(3), 200-210.
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  Abstract: The demand for the use of carbon-fiber-reinforced plastics (CFRP) in rehabilitation of deteriorating infrastructure is increasing worldwide. The design characteristics of reinforced concrete or steel members can be enhanced significantly by epoxy bonding CFRP laminates to the critically stressed tension areas. There is, however, a concern regarding possible galvanic corrosion when carbon and steel are bonded together. This paper presents the result of a study on the galvanic corrosion between CFRP laminates and steel. A total of 38 specimens made of steel and carbon fibers were prepared and tested. Two simulated aggressive environments and three different amounts of epoxy coating were used in addition to samples with no coating at all. Furthermore, the effect of the sizing agent on the galvanic corrosion rate was investigated, and three different solvents were used to remove the sizing agents from the surface of the carbon fibers. Potentiodynamic polarization and galvanic corrosion tests were conducted. The results of the experiments showed the existence of galvanic corrosion; however, the rate of such corrosion could be decreased significantly by epoxy coating.
• Velazquez-Dimas, J. I., Ehsani, M. R., & Saadatmanesh, H. (2000). Out-of-plane behavior of brick masonry walls strengthened with fiber composites. ACI Structural Journal, 97(3), 377-387.
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  Abstract: The vulnerability of unreinforced masonry buildings (URM) to moderate ground motions is a fact recognized by the earthquake engineering community. In this paper, an innovative retrofitting system for URM buildings using glass fiber reinforced polymer (GFRP) strips is investigated. The experimental results for four retrofitted URM walls subjected to cyclic out-of-plane loading are presented herein. The first three specimens were constructed in single wythe, and the fourth one in double wythe. The height-thickness ratio for all specimens was 28. Depending on the reinforcement ratio, single wythe walls failed in tension, excessive delamination, or a combination of both. Failure modes in the double wythe wall were peeling off of composite strips and splitting of the wythes. From experimental results, it was found that walls were capable of supporting pressures of up to 25 times their weight and deflect up to 1/20 times the wall height. Strength and deformation capacity of the walls were significantly improved by the investigated retrofitting technique.
• Ehsani, M. R., Saadatmanesh, H., & Velazquez-Dimas, J. (1999). Behavior of retrofitted URM walls under simulated earthquake loading. Journal of Composites for Construction, 3(3), 134-142.
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  Abstract: Unreinforced masonry (URM) buildings perform poorly under seismic forces and have been identified as the main cause of loss of life in recent earthquakes. Many of these structures fail in out-of-plane bending due to the lack of reinforcement. In this study, the experimental results from three half-scale unreinforced brick walls retrofitted with vertical composite strips are presented. The specimens were subjected to cyclic out-of-plane loading. Five reinforcement ratios and two different glass fabric composite densities were investigated. The mode of failure is controlled by tensile failure when wider and lighter composite fabrics are used and by delamination when stronger ones are used. The tested specimens were capable of supporting a lateral load up to 32 times the weight of the wall. A deflection as much as 2% of the wall height was measured. Although both URM walls and composite strips behave in a brittle manner, the combination resulted in a system capable of dissipating some energy. Retrofitting URM walls with composite strips proved to be a good and reliable strengthening alternative.
• Saadatmanesh, H., & Tannous, F. E. (1999). Long-term behavior of aramid fiber reinforced plastic (AFRP) tendons. ACI Materials Journal, 96(3), 297-305.
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  Abstract: The recent advancements in the fields of materials science and composites have resulted in the development of high-strength, corrosion-resistant fiber reinforced plastic (FRP) tendons that could potentially replace steel tendons in prestressed or post-tensioned concrete structures, particularly in areas where corrosion is a problem. The more common types of FRPs used in construction are made from high-strength filaments of glass, carbon, or aramid placed in a resin matrix. Each combination of fiber and resin presents a unique advantage for a particular application. In this paper, the behavior of aramid fiber reinforced plastic (AFRP) tendons will be examined. Test results of relaxation, creep, and fatigue behavior of 10-mm-(3/ 8-in.)-diameter AFRP tendons under simulated field conditions are presented. Twelve specimens were tested in air at temperatures of -30, 25, and 60 C, and 24 specimens were tested in alkaline, acidic, and salt solutions at temperatures of 25 and 60 C to evaluate the relaxation behavior. In addition, 45 specimens were tested in tension-tension fatigue to investigate the effect of repeated loading on the mechanical properties of the tendon, such as the elastic modulus E, Poisson's ratio V, and the residual tensile strength Pr. A preliminary investigation of the creep behavior was also conducted at room temperature in air, alkaline solution, and acidic solution. The fatigue and creep performance of the AFRP tendons tested in this study was very good. The relaxation losses were higher in solutions, as compared with those specimens tested in air. In particular, the losses in acidic solutions were the highest.
• Saadatmanesh, H., & Tannous, F. E. (1999). Relaxation, creep, and fatigue behavior of carbon fiber reinforced plastic tendons. ACI Materials Journal, 96(2), 143-153.
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  Abstract: Corrosion of steel tendons is a major problem in prestressed and posttensioned concrete structures. Fiber reinforced plastics (FRPs) are a promising alternative to steel due to their high tensile strength, light weight, and resistance to electrochemical corrosion. Different types of FRP tendons have been developed to potentially replace steel tendons in areas where corrosion is a problem. However, before field application of FRPs as prestressing elements, their long-term behavior must be investigated. This paper presents relaxation, creep, and tension-tension fatigue test results of two carbon fiber reinforced plastic (CFRP) tendons, namely, Leadline PC-D8 8-mm-(5/16-in.)-diameter, and 1 x 7-7.5-mm-(5/16-in.)-diameter carbon fiber composite cable (CFCC). Twelve Leadline and 12 CFCC tendon specimens were tested in air at temperatures of-30, 25, and 60 C to determine their relaxation behavior. In addition, the relaxation behavior of 24 Lead-line and 24 CFCC samples was examined in chemical solutions simulating aggressive field conditions. The loss of tensile force for the 3000 hr test duration at stress ratios of 0.4 and 0.6 was generally less than 10 percent, and it depended primarily on the initial stress level and the type and temperature of the environment. Preliminary investigation of creep behavior of Leadline and CFCC in air and in chemical solutions was also conducted. Six samples of Leadline and six samples of CFCC were subjected to sustained load at room temperature in air, in alkaline, and in acidic solutions, for a period of 3000 hr. Creep behavior of both tendons was good; however, the creep strains were higher in solutions than in air. Furthermore, 190 samples of Leadline and CFCC were tested in tension-tension fatigue to examine the effect of repeated loading on the modulus of elasticity. Poissons ratio, and the tensile strength of these types of tendons. Fatigue strength was generally good and depended on the stress range and initial stress level.
• Tannous, F. E., & Saadatmanesh, H. (1999). Durability of AR glass fiber reinforced plastic bars. Journal of Composites for Construction, 3(1), 12-19.
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  Abstract: Since the development of reinforced concrete over a century ago, engineers have constantly struggled with the corrosion problem of steel reinforcement. The new advances in the field of materials science have resulted in the development of fiber reinforced plastic (FRP) materials that could potentially be used as bars in reinforced concrete structures. The attractive features of this type of bars include high strength, light weight, and resistance to electrochemical corrosion. E-glass is the most widely used fiber material in FRPs; however, studies have shown that this type of fiber is susceptible to degradation in alkaline environments (i.e.; concrete). This paper presents the results of a durability study on FRP bars made from an alternative glass fiber, alkali resistant (AR) glass, that could potentially improve the durability of FRP bars. A total of 160 bar samples were tested after exposure to corrosive solutions at temperatures of 25°C and 60°C. These solutions were designed to simulate accelerated exposure to adverse conditions in the field. Test variables included two matrix materials (polyester and vinyl ester), seven chemical solutions, and ultraviolet radiation. Moisture absorption by bars and associated changes in the mechanical properties were the focus of this study. In addition, ten reinforced concrete beams were tested in flexure until failure, to examine the effects of exposure to concrete and deicing salts. Test results indicated that significant loss of strength could result from exposure of AR glass FRP bars to simulated aggressive field conditions. An analytical study based on diffusion models and Pick's law was also conducted to predict the loss of strength. In the Fickian range of diffusion, the models predicted the loss of strength with a reasonable accuracy. © ASCE, ISSN 1090-0268/99/0001-0012-0019/$8.00 + $.50 per page.
• Larsen, M. H., Saadatmanesh, H., & Ehsani, M. R. (1998). Non-destructive testing of wood using nuclear magnetic resonance (NMR) spectroscopy. Insight: Non-Destructive Testing and Condition Monitoring, 40(7), 505-512.
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  Abstract: This paper presents the results of a study utilising NMR to measure moisture content and strength of wood. Different species of wood at different moisture contents were evaluated. Standard destructive tests as well as non-destructive tests using NMR were conducted. Correlations were made between the results of destructive and non-destructive tests. As reported by other researchers also, an almost linear relationship was observed between the moisture content of wood and the intensity of magnetisation. Consistent trends were observed between the stress at failure of wood and the intensity of magnetisation of physical protons.
• Malek, A. M., & Saadatmanesh, H. (1998). Analytical study of reinforced concrete beams strengthened with web-bonded fiber reinforced plastic plates or fabrics. ACI Structural Journal, 95(3), 343-352.
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  Abstract: Bonding fiber reinforced plastic (FRP) plates or fabrics to the web of reinforced concrete beams can increase the shear and flexural capacity of the beam. This paper presents analytical models to calculate the stresses in the strengthened beam, and the shear force resisted by the composite plate before cracking and after formation of flexural cracks. The anisotropic (orthotropic) behavior of the composite plate or fabric has been considered in the analytical models. The companion paper extends this discussion into post cracking behavior at the ultimate load, where the diagonal shear cracks are formed. The method has been developed assuming perfect bond between FRP and concrete (i.e., no slip), and using compatibility of the strains in the FRP and the concrete beam. The validity of the assumptions used in this method has been verified by comparing the results to the finite element method. A parametric study has been performed to reveal the effect of important variable parameters, such as fiber orientation angle on the shear force resisted by the FRP plate. The method has been developed for both uncracked and cracked beams, and it can be used for stress analysis of these types of beams.
• Malek, A. M., & Saadatmanesh, H. (1998). On the analysis and design of reinforced concrete beams strengthened with FRP laminates. Arabian Journal for Science and Engineering, 23(2C), 167-182.
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  Abstract: Flexural and shear strength of reinforced concrete beams can be effectively increased by bonding a composite plate to the tension face or web of the beam. The plate undergoes tensile stresses and resists opening of the cracks. In this paper, experimental and analytical study of concrete beams strengthened with epoxy bonded fiber composite plate or fabric is reviewed. Guidelines and equations are also presented for flexural strengthening of concrete beams. Different modes of failure such as compression crushing of concrete, rupture of the plate and local shear failure have been considered in the development of the guidelines. The effect of web-bonded composite plate on the shear strength of the concrete beam is also discussed.
• Malek, A. M., & Saadatmanesh, H. (1998). Ultimate shear capacity of reinforced concrete beams strengthened with web-bonded fiber-reinforced plastic plates. ACI Structural Journal, 95(4), 391-399.
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  Abstract: The ultimate shear capacity of reinforced concrete beams can be increased by epoxy-bonding fiber-reinforced plastic (FRP) plates to web of the beam. The shear crack inclination angle is changed as a result of bonding of the plate. In this paper truss analogy and compression field theory are used to determine the effect of the FRP plate on the shear capacity and crack inclination angle of reinforced concrete beams at ultimate state. Following the calculation of the crack inclination angle, the equilibrium and compatibility equations are used to obtain the shear force resisted by the plate. A parametric study was carried out to reveal the effect of important parameters such as plate thickness and fiber orientation on the crack inclination angle and shear capacity. The upper bound value of crack inclination angle found in this study is suggested as a conservative value for determining the shear capacity of the retrofitted beam. Knowing the inclination angle of cracks, the shear force in the composite plate and concrete beam can be calculated and used for the design of this type of beam. The results of this method have shown close agreement to experimental results.
• Malek, A. M., Saadatmanesh, H., & Ehsani, M. R. (1998). Prediction of failure load of R/C beams strengthened with FRP plate due to stress concentration at the plate end. ACI Structural Journal, 95(2), 142-152.
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  Abstract: Epoxy-bonding a composite plate to the tension face is an effective technique for repair and retrofit of reinforced concrete beams. Experiments have indicated local failure of the concrete layer between the plate and longitudinal reinforcement in retrofitted beams. This mode of failure is caused by local stress concentration at the plate end as well as at the flexural cracks. This paper presents a method for calculating shear and normal stress concentration at the cutoff point of the plate. This method has been developed based on linear elastic behavior of the materials. The effect of the large flexural cracks along the beam has also been investigated. The model has been used to find the shear stress concentration at these cracks. The predicted results have been compared to both finite element method and experimental results. The analytical models provide closed form solutions for calculating stresses at the plate ends that can easily be incorporated into design equations.
• Saadatmanesh, H., & Malek, A. M. (1998). Design guidelines for flexural strengthening of RC beams with FRP plates. Journal of Composites for Construction, 2(4), 158-164.
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  Abstract: Bonding composite plates to reinforced concrete beams is an effective technique of repair and retrofit. The ultimate capacity of the strengthened beam is controlled by either compression crushing of concrete, rupture of the plate, local failure of concrete at the plate end due to stress concentration, or debonding of the plate. These failure modes have been considered for developing design guidelines for strengthening reinforced concrete beams using fiber composite plates. The effect of multistep loading of the beam, before and after upgrading, has been included in these guidelines. Limit state design concept has been followed in this paper. Terms, definitions, and notations compatible to design guidelines for ordinary reinforced concrete beams have been used.
• Saadatmanesh, H., & Tannous, F. (1998). Durability of fiber reinforced plastic (FRP) rebars and tendons in aggresive environments. Proceedings of the International Seminar on Repair and Rehabilitation of Reinforced Concrete Structures: The State of the Art, 120-133.
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  Abstract: This paper presents the durability test results of various commercially available composite rebars and tendons. The durability of eight different combinations of glass fiber reinforced plastic (GFRP) rebars, as well as, two carbon fiber reinforced plastic (CFRP) tendons, and one aramid fiber reinforced plastic (AFRP) tendon was examined. Tendon and rebar specimens were directly exposed to seven different solutions simulating accelerated exposure to various field conditions. Test results indicated long-term durability problems associated with GFRP rebars, while CFRP and AFRP tendons displayed excellent durability in harsh environments. The free-phase model (i.e. Fick's law) of diffusion showed to be an acceptable model to approximately predict the losses in tensile strength of composite rebars and tendons.
• Tannous, F. E., & Saadatmanesh, H. (1998). Environmental effects on the mechanical properties of E-glass FRP rebars. ACI Materials Journal, 95(2), 87-100.
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  Abstract: Due to their unique properties, fiber reinforced plastics (FRPs) are becoming increasingly popular among researchers and engineers in the construction industry. FRP rebars in particular present an attractive alternative to steel rebars in reinforced concrete. Among the features of this type of rebar are the high strength-to-weight ratio and potential resistance to aggressive environmental factors. This paper presents the results of an experimental and analytical study on the durability of E-glass FRP rebars. A total of 160 rebar samples were placed in corrosive chemical solutions that simulated exposure in the field. Tests were performed at temperatures of 25 C and 60 C. Test variables included one type of fiber (E-glass), two matrix materials (polyester and vinylester), seven chemical solutions, and ultraviolet radiation. Rebar specimens were constructed from E-glass fibers embedded in polyester or vinylester resin matrix. Rebar sizes were 10 mm (3/8 in.) and 19.5 mm (3/4 in.) in diameter. Changes in weight and physical appearance were recorded over a one-year period. In addition, ten beams each reinforced with two 10-mm (3/8-in.) E-glass/polyester or E-glass/vinylester FRP rebars were subjected to deicing salt solutions. They were tested in flexure to failure after one-year and two-year periods, and the load versus mid-span deflection relationships were recorded. Test results of rebars and beams indicate that significant loss of strength can result from the exposure of E-glass FRP rebars.
• Ehsani, M. R., & Saadatmanesh, H. (1997). Fiber composites: An economical alternative for retrofitting earthquake-damaged precast-concrete walls. Earthquake Spectra, 13(2), 225-241.
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  Abstract: A new approach for seismic retrofitting of lightly-reinforced precast-concrete walls is presented. The technique involves epoxy bonding the reinforcing material (composite fabric) to the exterior surface of the wall. The flexible light-weight fabrics are extremely strong in tension and can significantly increase the flexural and shear capacity of the member. The thin composite fabrics cause little increase in the weight and thickness of the wall, causing little change to the inertial loads and eliminating the need for strengthening of the footings. Following the January 17, 1994 Northridge earthquake, this technique was applied to a tilt-up concrete building in southern California. The method proved to be the most cost-effective alternative to repair this damaged building in a very short time. More than 20,000 ft.2 of wall surface area were strengthened, making this project the largest reported application of this technique. This paper discusses some of the design considerations and the strengthening of the damaged building.
• Ehsani, M. R., Saadatmanesh, H., & Al-Saidy, A. (1997). Shear behavior of URM retrofitted with FRP overlays. Journal of Composites for Construction, 1(1), 17-25.
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  Abstract: A large inventory of older masonry buildings exists in earthquake-prone regions. In most cases these buildings contain shear walls constructed of unreinforced masonry. The majority of these buildings were built before any provisions for earthquake loadings were established. The failures and damages reported in recent earthquakes attest to the need for efficient strengthening procedures. The effectiveness of increasing the shear strength of brick masonry by epoxy-bonding fiber-reinforced polymer (FRP) overlays to the exterior surfaces was evaluated. The variables in the test included the strength of the composite fabric, fiber orientation, and anchorage length. The specimens were tested under static loading. The results showed that both the strength and ductility of tested specimens were significantly enhanced with this technique. The orientation of the angle of fibers with respect to the plane of loading had a major effect on the stiffness of the retrofitted system but did not affect the ultimate strength significantly.
• Ehsani, M. R., Saadatmanesh, H., & Nelson, C. T. (1997). Transfer and flexural bond performance of aramid and carbon FRP tendons. PCI Journal, 42(1), 76-86.
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  Abstract: The use of non-corrosive fiber reinforced polymer (FRP) composite materials as reinforcement for concrete structures has been growing in recent years. This study, conducted at the Federal Highway Administration Laboratories, compared the transfer length and flexural bond behavior of five commercially available FRP tendons. Three of the tendons had aramid as the main reinforcement, and the other two included carbon fibers. Sixteen specimens, including a control specimen reinforced with a high strength steel tendon, were tested. It is shown that the transfer length for FRP tendons is generally shorter than that for steel. For the aramid tendons, the ACI equations result in a conservative estimation of the development length; however, this is not true for the carbon tendons examined. The efficiency of the various grips and the loss of prestress for each of the tendons is also discussed.
• Ehsani, M. R., Saadatmanesh, H., & Tao, S. (1997). Bond behavior of deformed GFRP rebars. Journal of Composite Materials, 31(14), 1413-1430.
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  Abstract: The bond behavior of straight Glass-Fiber-Reinforced-Plastic (GFRP) reinforcing bars to concrete was experimentally investigated. Results of 48 beam and 18 pull-out specimens constructed with No. 3, 6, and 9 GFRP rebars are presented. The static tensile load was applied to the rebars in a gradual increment of load level until splitting failure of concrete, rebar pull out failure, or rebar fracture occurred. The slip between the rebars and concrete was measured at the loaded and free ends at each load level. Variables in the study included concrete compressive strength, embedment length, clear concrete cover, rebar diameter, and concrete cast depth. On the basis of the experimental results, it was concluded that the ultimate bond stress increases with higher concrete compressive strength and clear concrete cover, but decreases with larger concrete cast depth. The ultimate bond stress and the loaded end slip of the pull-out specimens were found to be greater than that of the beam specimens. Beam test data could be more realistic and accurate for use in determining the development length.
• Norris, T., Saadatmanesh, H., & Ehsani, M. R. (1997). Shear and flexural strengthening of R/C beams with carbon fiber sheets. Journal of Structural Engineering, 123(7), 903-911.
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  Abstract: The results of an experimental and analytical study of the behavior of damaged or understrength concrete beams retrofitted with thin carbon fiber reinforced plastic (CFRP) sheets are presented. The CFRP sheets are epoxy bonded to the tension face and web of concrete beams to enhance their flexural and shear strengths. The effect of CFRP sheets on strength and stiffness of the beams is considered for various orientations of the fibers with respect to the axis of the beam. Nineteen beams were fabricated, loaded beyond concrete cracking strength, and retrofitted with three different CFRP systems. The beams were subsequently loaded to failure. Different modes of failure and gain in the ultimate strength were observed, depending on the orientation of the fibers.
• Saadatmanesh, H. (1997). Extending service life of concrete and masonry structures with fiber composites. Construction and Building Materials, 11(5-6), 327-335.
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  Abstract: Considering the deteriorating state of the infrastructure worldwide and the limited resources available for repair and rehabilitation of constructed facilities, it is imperative to find effective and economical techniques to revive the aging infrastructure. In this paper, the utilization of modern materials such as fiber reinforced plastics (FRP) for strengthening and rehabilitation of concrete and masonry structures is presented. Three different applications of FRPs will be discussed. In one application, composite plates are epoxy bonded to the soffit of girders to increase their ultimate strength. The results of an analytical and experimental study on ten 4.88 m long girders indicate that significant strength gains can be achieved with this retrofitting technique. In the second study, FRP straps are used as external confinement for enhancing seismic response of concrete bridge columns. Ten columns were subjected to simulated earthquake loading. The results of the hysteresis loops of retrofitted columns, when compared to those for unretrofitted control specimens, revealed gain in ductility level of up to four times. In the third study, composite fabrics were epoxy bonded to the faces of unreinforced masonry walls to improve their in-plane and out-of-plane responses during seismic loading. Significant improvements in the behavior were also observed for this technique. © 1997 Elsevier Science Ltd.
• Saadatmanesh, H., & Ehsani, R. (1997). Non-destructive evaluation of concrete and wood properties using NMR. Insight: Non-Destructive Testing and Condition Monitoring, 39(2), 75-82.
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  Abstract: In this paper, a preliminary investigation of the Nuclear Magnetic Resonance (NMR) technique for non-destructive evaluation of concrete and wood is made. Basic principles of NMR are discussed. Samples of concrete and wood were tested using NMR. In these tests, the hydration process in concrete and the moisture content of wood samples were monitored. In addition, standard destructive testing of these materials was conducted to determine their failure strengths. The results of destructive tests were compared with those of NMR testings. Good correlation was observed between the results of non-destructive NMR and standard destructive tests.
• Saadatmanesh, H., Ehsani, M. R., & Jin, L. (1997). Repair of earthquake-damaged RC columns with FRP wraps. ACI Structural Journal, 94(2), 206-X.
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  Abstract: An investigation was conducted into the flexural behavior of earthquake-damaged reinforced concrete columns repaired with prefabricated fiber reinforced plastic (FRP) wraps. Four column specimens were tested to failure under reversed inelastic cyclic loading to a level that can be considered higher than would occur in a severe earthquake. The columns were repaired with prefabricated FRP wraps and retested under simulated earthquake loading. The test specimens were designed to model single-bent, nonductile concrete columns in existing highway bridges constructed before the modern seismic design provisions were in place. FRP composite wraps were used to repair damaged concrete columns in the critically stressed areas near the column footing joint. The physical and mechanical properties of FRP composite wraps are described. Seismic performance of repaired columns in terms of their hysteretic response is evaluated and compared to those of the original and unretrofitted columns. The results indicate that the proposed repair technique is highly effective. Both flexural strength and displacement ductility of repaired columns were higher than those of the original columns.
• Saadatmanesh, H., Ehsani, M. R., & Jin, L. (1997). Seismic retrofitting of rectangular bridge columns with composite straps. Earthquake Spectra, 13(2), 281-304.
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  Abstract: Behavior of typical rectangular bridge columns with substandard design details for seismic forces was investigated. The poor performance of this type of column attested to the need for effective and economical seismic upgrading techniques. A method utilizing fiber reinforced polymer (FRP) composites to retrofit existing bridge columns is investigated in this paper. High-strength FRP straps are wrapped around the column in the potential plastic hinge region to increase confinement and to improve the behavior under seismic forces. Five rectangular columns with different reinforcement details were constructed and tested under reversed cyclic loading. Two columns were not retrofitted and were used as control specimens so that their hysteresis response could be compared with those for retrofitted columns. The results of this study indicated that significant improvement in ductility and energy absorption capacity can be achieved as a result of this retrofitting technique.
• Ehsani, M. R., Saadatmanesh, H., & Tao, S. (1996). Design recommendations for bond of GFRP rebars to concrete. Journal of Structural Engineering, 122(3), 247-254.
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  Abstract: To develop design guidelines for bond of glass-fiber-reinforced plastic (GFRP) rebars to concrete, a total of 102 specimens were constructed and tested subjected to monotonic static loading. The research program was inclusive of the experimental testing of 48 beam specimens, 18 pull-out specimens, and 36 hooked rebar specimens. The tensile load was applied to the rebars in a gradual increment of load level until splitting of concrete, rebar pull-out failure, or rebar fracture occurred. The slip between the rebars and concrete was measured at the loaded and free ends at each load level. Variables included in the study were concrete compressive strength, embedment length, clear concrete cover, rebar diameter, concrete cast depth, radius of bend, and tail length. New criteria for acceptable bond performance of GFRP rebars to concrete were developed and were used to evaluate the experimental results. Design guidelines for calculating the development lengths for straight and hooked GFRP rebars to concrete were derived. In addition, confinement factors were calculated to reflect the influence of concrete cover and casting position.
• Saadatmanesh, H., Ehsani, M. R., & Jin, L. (1996). Seismic strengthening of circular bridge pier models with fiber composites. ACI Structural Journal, 93(6), 639-647.
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  Abstract: An experimental investigation was conducted to study the seismic behavior of reinforced concrete columns strengthened with fiber reinforced plastic (FRP) composite straps. Five concrete column-footing assemblages were constructed with a 1/5-dimensional scale factor. The unidirectional glass fabric straps were impregnated with polyester resin and wrapped around the potential plastic hinge zone of the columns. An epoxy layer was applied to the straps while wrapping for interlaminar bond. All specimens were tested under inelastic reversal loading while simultaneously subjected to a constant axial load. Test results show that seismic resistance of retrofit concrete columns improves significantly as a result of the confining action of the FRP composite straps. The straps are highly effective in confining the core concrete and preventing the longitudinal reinforcement bars from buckling under cyclic loading.
• Albrecht, P., Wulin, L. i., & Saadatmanesh, H. (1995). Fatigue strength of prestressed composite steel-concrete beams. Journal of structural engineering New York, N.Y., 121(12), 1850-1856.
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  Abstract: Effective prestressing increases the strength of existing composite steel-concrete bridges. Investigators have determined the static strength of prestressed composite girders, but without addressing fatigue strength - an important design factor in highway bridges. In this paper, 11 prestressed composite beams with a cover plate welded to the tension flange were prestressed with two seven-wire strands. In fatigue tests to failure, cracks initiated in the flange at the cover-plate ends. Stress ranges in the strands and at the base of the shear studs were too small to initiate cracks. Prestressing of the steel beam so that the stress in the tension flange alternates between tension and compression under cyclic loading raised the fatigue strength of the welded cover plates by one category, from D to C.
• Saadatmanesh, H., Ehsani, M. R., & Yanez, J. C. (1995). Hydration and early-age strength measurement of concrete using nuclear magnetic resonance (NMR). Nondestructive Testing and Evaluation, 12(2), 133-153.
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  Abstract: A new nondestructive technique for monitoring the hydration process of cement within concrete and measurement of the compressive strength of concrete is presented. The technique called the Nuclear Magnetic Resonance (NMR) has so far been primarily used in the fields of chemistry and medicine. Its application to construction materials has been very limited or nonexistent. In this study, NMR is used to monitor the hydration of cement paste in concrete with two different water cement ratios. The first objective of this study was to distinguish between the amounts of remaining free water, and water consumed in the hydration process during the 28 days monitoring period. The second objective was to relate the compressive strength of concrete to NMR signals. A number of standard compression tests were performed in parallel with the NMR tests. Correlation of the responses from nondestructive tests with NMR and those of standard compression tests indicated almost a linear relationship.
• Wulin, L. i., Albrecht, P., & Saadatmanesh, H. (1995). Strengthening of composite steel-concrete bridges. Journal of structural engineering New York, N.Y., 121(12), 1842-1849.
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  Abstract: The concept of prestressing has been used as an effective technique to strengthen composite steel-concrete girders in bridges and buildings. Although several researchers have investigated the behavior of this structural system under static loading, no one has addressed the fatigue behavior. This paper analyzes and summarizes the fatigue test data for the main constituent components of prestressed composite steel-concrete girders - strands, shear studs, and cover plates. The data are also compared with the American Association of State Highway and Transportation Officials (AASHTO) requirements. It appears that end-anchored strands for nonbonded, prestressed structures can be designed for fatigue to the AASHTO allowable stress range for category C. AASHTO's approach to designing shear studs and cover plates seems reasonable for prestressed composite girders. A companion paper presents the fatigue behavior of these elements within a prestressed composite girder.
• Jin, L., Saadatmanesh, H., & Ehsani, M. R. (1994). Seismic retrofit of existing reinforced concrete columns by glass-fiber composites. Proceedings of the Materials Engineering Conference, 758-763.
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  Abstract: A seismic retrofitting method to enhance the flexural strength, ductility capacity and shear resistance of existing reinforced concrete bridge columns through externally reinforcing the column with advanced composite materials (ACM) is presented. Test results of ten scaled-down concrete columns indicate that the confinement and the lateral stresses induced by the ACM straps significantly increased the shear strength and ductility capacity, and greatly improved the flexural behavior of reinforced concrete columns under simulated earthquake loading.
• Saadatmanesh, H. (1994). Fiber composites for new and existing structures. ACI Structural Journal, 91(3), 346-354.
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  Abstract: Fiber composite materials have been used in a variety of industries, such as aerospace, automotive, shipbuilding, chemical processing, etc., for many years. Their application in civil engineering, however, has been very limited. Their high strength-to-weight ratio and excellent resistance to electrochemical corrosion make them attractive materials for structural applications. This paper presents an overview of some of the applications of nonmetallic, fiber composites in concrete construction.
• Saadatmanesh, H., Ehsani, M. R., & Li, M. W. (1994). Strength and ductility of concrete columns externally reinforced with fiber composite straps. ACI Structural Journal, 91(4), 434-447.
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  Abstract: Bridge failures in recent earthquakes such as the 1989 Loma Prieta earthquake have attracted the attention of the bridge engineering community to the large number of bridges with substandard seismic design details. Many concrete columns in bridges designed before the new seismic design provisions were adopted have low flexural ductility, low shear strength, and inadequate lap length for starter bars. These problems, compounded by flaws in the design of structural systems, have contributed to the catastrophic bridge failures in recent earthquakes. In this paper, a new technique for seismic strengthening of concrete columns is presented. The technique requires wrapping thin, flexible high-strength fiber composite straps around the column to improve the confinement and, thereby, its ductility and strength. Analytical models are presented that quantify the gain in strength and ductility of concrete columns externally confined by means of high-strength fiber composite straps. A parametric study is conducted to examine the effects of various design parameters such as concrete compressive strength, thickness and spacing of straps, and type of strap. The results indicate that the strength and ductility of concrete columns can be significantly increased by wrapping high-strength fiber composite straps around the columns.
• Ayyub, B. M., Sohn, Y. G., & Saadatmanesh, H. (1992). Prestressed composite girders. I: experimental study for negative moment. Journal of structural engineering New York, N.Y., 118(10), 2743-2762.
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  Abstract: Limited experimental results were reported in the literature on the behavior of prestressed composite girders subjected to negative bending moment. This paper examines experimentally the behavior of prestressed composite steel-concrete girders. The steel beams were all welded plate girders. Five composite specimens were tested to study the various aspects of prestressed composite girders, including the effects of construction stages, prestressing sequence, tendon type, and compactness of the plate girders on their structural performance. Load versus midspan deflection, strains in the concrete deck and steel girder, and the force increase in the prestressing tendons due to the applied loads were measured and studied. The test results showed that prestressing a composite girder in the negative moment region increases its stiffness by preventing the cracking of concrete under service loads; enlarges the elastic range; and increases the ultimate capacity due to the effective use of high-strength tendons.
• Ayyub, B. M., Sohn, Y. G., & Saadatmanesh, H. (1992). Prestressed composite girders. II: analytical study for negative moment. Journal of structural engineering New York, N.Y., 118(10), 2763-2783.
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  Abstract: A method for the structural analysis of prestressed composite steel-concrete girders was studied in this paper. The deflections, forces in the prestressing tendons, and strains in the steel beam and concrete slab of composite girders were computed throughout the entire loading range up to failure. Equations are provided for the calculation of the yield and ultimate load capacities of the girders. The developed analytical models were based on the incremental deformation method. The results of the analytical study were compared with test results of several girders. Reasonably good correlations between analytical and experimental results were obtained. Also, the results showed that a substantial increase in the yield and an increase in the ultimate load capacities can be achieved by adding prestressing tendons to the composite girders and prestressing them. It was determined that the most effective construction sequence for prestressed composite girders in negative moment regions i to posttension the composite girders with tendons in the concrete slabs.
• Desai, C. S., Saadatmanesh, H., & Allen, T. (1992). Behavior of compacted lunar simulants using new vacuum triaxial device. Journal of Aerospace Engineering, 5(4), 425-441.
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  Abstract: Development and study of mechanical properties of engineering materials from locally available materials in space is a vital endeavor toward establishment of bases on the Moon and other planets. The objectives of this study are to create a lunar simulant locally from a basaltic rock, and to design and develop a new vacuum triaxial test device that can permit testing of compacted lunar simulant under cyclic loading with different levels of initial vacuum. Then, triaxial testing is performed in the device itself without removing the compacted specimen; this is achieved by a special mechanism installed within the device. Preliminary constrained compression and triaxial shear tests are performed to identify effects of initial confinements and vacuums. The results are used to define deformation and strength parameters. At this time, vacuum levels up to 10-4 are possible; subsequent research should involve higher vacuum levels, e.g., 10-14 torr as they occur on the Moon. The research can have significant potential toward development of methodology so as to develop compacted materials for various construction applications, and also toward stress-strain-strength testing of lunar simulants with different vacuum levels.
• Desai, C. S., Saadatmanesh, H., & Allen, T. (1992). Mechanical properties of compacted lunar simulant using new vacuum triaxial equipment. Array, 1240-1249.
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  Abstract: Mechanical stress-strain-strength properties of Arizona Lunar Simulant (ALS) are investigated by using a newly developed vacuum triaxial device that allows compaction under different initial vacuums and confinements. Influence of vacuum and confinement on compaction, strength and deformation characteristics of compacted material are delineated and discussed.
• Li, M. W., Saadatmanesh, H., & Ehsani, M. R. (1992). Behavior of externally confined concrete columns. Materials: Performance and Prevention of Deficiencies and Failures, 677-690.
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  Abstract: This paper investigates the feasibility of strengthening of seismically deficient concrete columns with high-strength fiber composite straps. The concrete columns will be externally confined by wrapping thin glass-fiber-reinforced or carbon-fiber-reinforced straps around the column. The confinement provided by the straps will increase the stress and strain of concrete at failure and will increase its ductility. Moreover, the composite strap will prevent buckling of longitudinal bars and spalling of the shell and therefore will further increase the load carrying capacity of the column. Analytical models are developed and a seismically deficient parametric study is conducted to investigate the effectiveness of this technique for strengthening of concrete columns designed before the new seismic design provisions and codes were in place. The variables used in the parametric study include, concrete compressive strength, thickness of composite strap, clear spacing between composite straps and type of the composite strap, i.e., carbon fiber reinforced or glass fiber reinforced. The results indicate that external confinement provided by the composite straps significantly increases the strength and ductility of concrete columns.
• Tao, S., Ehsani, M. R., & Saadatmanesh, H. (1992). Bond strength of straight GFRP rebars. Materials: Performance and Prevention of Deficiencies and Failures, 598-605.
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  Abstract: An overview of a study on bond of straight Glass-fiber-reinforced-plastic (GFRP) rebars to concrete is presented. The 54 specimens to be tested include several variables, such as the mode of failure (i.e. pullout or splitting), concrete compressive strength, bar diameter, clear cover distance, and top bar effects. The study is currently in progress and the results of those specimens tested to date are presented.
• Saadatmanesh, H., & Ehsani, M. R. (1991). Fiber composite bar for reinforced concrete construction. Journal of Composite Materials, 25(2), 188-203.
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  Abstract: Behavior of concrete beams reinforced with Glass-Fiber-Reinforced-Plastic (GFRP) bars was experimentally investigated. Two types of reinforcements were considered; longitudinal or flexural reinforcement and transverse or shear reinforcement. For each of the two types of reinforcements, three concrete beams were tested to failure. The behavior of each beam was characterized by its load-deflection response to failure. The study was mainly focused on experimentally determining the feasibility of GFRP bars as reinforcement for concrete structures. The results indicated that the plastic bars performed reasonably well in the beams tested.
• Saadatmanesh, H., & Ehsani, M. R. (1991). RC beams strengthened with GFRP plates. I. Experimental study. Journal of structural engineering New York, N.Y., 117(11), 3417-3433.
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  Abstract: The static strength of reinforced concrete beams strengthened by gluing glass-fiber-reinforced-plastic (GFRP) plates to their tension flanges is experimentally investigated. Five rectangular beams and one T-beam were tested to failure under four-point bending. The measured load versus strain in GFRP plate, steel rebar, extreme compression fiber of concrete, and the load versus deflection for the section at midspan of the beams are plotted and compared to the predicted values. The results indicate that the flexural strength of RC beams can be significantly increased by gluing GFRP plates to the tension face. In addition, the epoxy bonded plates improved the cracking behavior of the beams by delaying the formation of visible cracks and reducing crack widths at higher load levels.
• Wei, A. n., Saadatmanesh, H., & Ehsani, M. R. (1991). RC beams strengthened with FRP plates. II. Analysis and parametric study. Journal of structural engineering New York, N.Y., 117(11), 3434-3455.
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  Abstract: Analytical models based on the compatibility of deformations and equilibrium of forces are presented to predict the stresses and deformations in concrete beams strengthened with fiber composite plates epoxy-bonded to the tension face of the beams. The models are given for beams having rectangular and T cross sections. A parametric study is conducted to investigate the effects of design variables such as plate area, plate stiffness and strength, concrete compressive strength, and steel reinforcement ratio. The moment versus curvature diagrams for various combinations of these variables are plotted and compared. The results indicate that bonding composite plate to a concrete beam can increase the stiffness, yield moment, and flexural strength of the beam. The method is particularly effective for beams with a relatively low steel reinforcement ratio.
• Avyub, B. M., & Saadatmanesh, H. (1990). Prestressed composite girders under positive moment. Journal of structural engineering New York, N.Y., 116(11), 2931-2951.
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  Abstract: According to the 1986 U.S. Federal Highway Administration statistics, there are 575,607 bridges on the highway system. About half of these bridges are structurally deficient and/or functionally obsolete. To strengthen the structurally deficient bridges without replacing the girders, external prestressing techniques can be used. In this paper, the behavior of prestressed, composite steel-concrete beams under positive bending moment is examined, and the benefits of different types of prestressing are compared. These specimens were tested to study various aspects of prestressed composite girders, including tendon type and profile. Two methods of analysis are discussed, i.e., the transformed area method and the strain compatibility method. The test results show that prestressing a composite girder increases the range of elastic behavior, reduces deflections, increases ultimate strength, and adds to the redundancy by providing multiple stress paths. Based on the experimental results, a comparison was made between three tendon types and profiles. It was concluded that strands are more effective than bars for the tendon type, and a straight tenden profile is more effective than a draped profile with regard to stiffness.
• Ehsani, M. R., & Saadatmanesh, H. (1990). Fiber composite plates for strengthening bridge beams. Composite Structures, 15(4), 343-355.
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  Abstract: Although the use of Glass Fiber Reinforced Plastics (GFRP) has increased significantly in recent years, its application in civil engineering has been limited at best. The high strength of GFRP and its resistance to corrosion makes it a suitable candidate in many applications where steel has been predominantly used in the past. In this study, five reinforced concrete beams were strengthened by epoxy-bonding GFRP plates along the tension flange of the beams. The load versus deflection curves to failure and the behavior of each specimen under static loading is presented. It is shown that the method presents great potential for solving some of the global problems facing the aging infrastructure. © 1990.
• Saadatmanesh, H., & Ehsani, M. R. (1990). Fiber composite plates can strengthen beams. Concrete International, 12(3), 65-71.
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  Abstract: A shortcoming of the method of adding epoxy-bonded steel plates to the tension face of concrete girders is the danger of corrosion at the epoxy-steel interface, which adversely affects the bond strength. An effective way of eliminating the corrosion problem is to replace steel plates with corrosion-resistant synthetic materials such as fiber composites. In addition to corrosion resistance, many fiber composites have tensile and fatigue strengths that exceed those of steel. Five beams were used to test the static strength of concrete beams strengthened with epoxy-bonded GFRP plates. Strengthening concrete beams with epoxy bonded GFRP plates appears to be a feasible way of increasing the load carrying capacity of existing bridges.
• Saadatmanesh, H., & Ehsani, M. R. (1990). Flexural strength of externally reinforced concrete beams. Array, 1152-1161.
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  Abstract: Results from tests of one rectangular and one T-beam are reported. The beams were strengthened by epoxy-bonding a 1/4 in. (6 mm) thick Glass Fiber Reinforced Plastic plate along the tension face. It is shown that the nominal load carrying capacity of the beams was significantly increased. The parametric study presented indicates that the method is most effective when applied to beams with low flexural steel reinforcement ratios.
• Ehsani, M. R., & Saadatmanesh, H. (1989). Behavior of externally prestressed concrete girders. Array, 218-222.
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  Abstract: A new technique for prestressing concrete girders is presented. The girders are externally prestressed by epoxy-bonding fiber-composite plates to the tension flange of the cambered girders. This technique can be applied to single-span as well as continuous-span girders. Four 8 in. × 18 in. rectangular beams with a clear span of 15 feet have been constructed. The beams will be tested to failure after they are externally prestressed by bonding fiber-composite plates along their full lengths. The load-deflection behavior of these beams will be analyzed.
• Saadatmanesh, H., & Ehsani, M. R. (1989). Application of fiber-composites in civil engineering. Array, 526-535.
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  Abstract: Two potential applications of Glass-Fiber-Reinforced-Plastics (GFRP) in civil engineering type structures are investigated: (1) GFRP rebars in concrete beams; (2) strengthening of concrete girders with epoxy-bonded GFRP plates. Six concrete beams reinforced with GFRP bars were tested for flexure and shear. The load-deflection behavior to failure and cracking behavior of these beams are discussed. It is concluded that GFRP rebars may successfully be used as reinforcing elements for concrete members. In the second part of the study, four reduced-scale girders were tested to establish the feasibility of strengthening of existing concrete girders with epoxy-banded GFRP plates, and to select an appropriate epoxy for this application. Significant increase in the ultimate capacity of the upgraded girders was observed.
• Saadatmanesh, H., Albrecht, P., & Ayyub, B. M. (1989). Analytical study of prestressed composite beams. Journal of structural engineering New York, N.Y., 115(9), 2364-2381.
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  Abstract: This paper analyzes the behavior of steel beams prestressed with high-strength steel tendon and compositely connected to a concrete deck. In particular, the deflection and the strains in the steel beam, concrete deck, and tendons are calculated in the positive and negative bending moment regions, over the full range of loading to failure. Three types of composite beams are considered: (1) Conventional composite beam without prestressing tendon; (2) composite beam with tendons anchored at the ends, but not prestressed; and (3) composite beam with tendons prestressed. The load-deflection and the load-strain behavior of these beams are compared. The analysis shows that the ultimate and the yield loads can be increased substantially by adding high-strength tendons to the composite beams and prestressing them.
• Saadatmanesh, H., Albrecht, P., & Ayyub, B. M. (1989). Experimental study of prestressed composite beams. Journal of structural engineering New York, N.Y., 115(9), 2348-2363.
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  Abstract: The concept of prestressing steel structures has only recently been widely considered, despite a long and successful history of prestressing concrete members. Several analytical studies of prestressed composite beams were reported in the literature, but much of that work was not experimentally verified. In particular, no test results were found on prestressed composite beams subjected to negative bending moment. This paper examines experimentally the behavior of prestressed, composite steel-concrete beams. Two beams were tested, one subjected to positive bending moment and the other to negative bending moment. The load was plotted against the deflection, and the strains in the concrete, steel beam, and prestressing bars. The values predicted with the equations of internal force equilibrium and compatibility between the deformations of the bars and the composite beam were found to correlate well with the measured data.
• Saadatmanesh, H., Albrecht, P., & Ayyub, B. M. (1989). Guidelines for flexural design of prestressed composite beams. Journal of structural engineering New York, N.Y., 115(11), 2944-2961.
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  Abstract: Prestressed steel has only recently been considered in the design of structures, despite a long, successful history of prestressed concrete structures. prestressing the steel in a composite steel-concrete beam increases the load at which the steel beam yields, and also increases the ultimate strength of the composite section. At the same time, precompressing the tension flange reduces the effective stress-range cycle and improves the fatigue strength. Prestressed composite beams can be used in new structures as well as for the strengthening of existing structures. Several analytical studies of single-span prestressed composite beams are reported in the literature, but no comprehensive design methodologies are given. This paper presents guidelines and equations for the design of prestressed composite beams in positive- and negative-moment regions. In the positive-moment region, a steel beam is prestressed first and then compositely connected to concrete deck. In the negative-moment region, a steel beam is prestressed and then compositely connected to a precast, prestressed concrete deck panel. The guidelines and equations are given for working-stress and load-factor design methods and are presented is a manner suitable for easy use by bridge-design engineers. A design example is also given to demonstrate the benefits of prestressing for strengthening existing bridges.