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Maragakis, Emmanuel M. - One of the best experts on this subject based on the ideXlab platform.
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Effects of Hinge Restrainers on the Response of the San Gregorio Bridge during the Loma Prieta Earthquake
9999Co-Authors: Maragakis, Emmanuel M., Saiidi, Mehdi S., Feng Shiping, Flournoy LindaAbstract:Report No. CCEER-93-5The primary objective of this study is to study the effects of cable Restrainers on the nonlinear seismic response of the San Gregorio Bridge. The computer program NEABS-86 was used in the nonlinear analyses. The earthquake analyses focus on the relative displacements at the hinges, the Restrainer stresses, and the abutment forces in both the longitudinal and the transverse directions of the bridge. The peak ground acceleration of the earthquake input, the seismic retrofit, the Restrainer gap, and the hinge gap were varied. It was found that, in general, the cable Restrainer system reduces the hinge responses in both the longitudinal and the transverse directions. Also found was that, when a zero Restrainer gap is assumed, the hinge responses change significantly. It is recommended that the Restrainer design be based on cases with both zero and non-zero Restrainer gaps, to encompass all the critical forces, stresses and displacements. Finally, some design methods for the longitudinal Restrainer cable at intermediate hinges of the bridge were evaluated. A modified "Dynamic-Caltrans" design procedure was tested preliminarily, and showed some promising results (Abstract by authors)
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An Evaluation of the Current Caltrans Seismic Restrainer Design Method
9999Co-Authors: Saiidi, Mehdi S., Maragakis, Emmanuel M., Feng ShipingAbstract:Report No. CCEER-92-8The primary objective of this study was to develop an understanding of the implications of the current Caltrans hinge Restrainer design procedure. Two aspects of the problem were studied. One was the effects of changing (a) the cross sectional area of Restrainers and (b) the Restrainer gap on the nonlinear response of a bridge with several hinges. The other was the sensitivity of the number of required Restrainers to changes in some of the simplifying assumptions which are made in the current Caltrans Restrainer design method. Computer program NEABS-86 was used in the nonlinear analyses [3]. The focus of this part of the study was the relative displacements at the joints, Restrainer forces, and Restrainer stresses. Three earthquake records, the El Centro 1940, Eureka 1954, and Saratoga 1989. In addition to input earthquakes, the number of Restrainers at each hinge, the Restrainer gaps, and the hinge gaps were varied. It was found that when a Restrainer gap of 0.75 in. is assumed, the number of Restrainers does not affect the response significantly. It is recommended that the design should be based on cases with and without Restrainer gaps to encompass all the critical forces, stresses, and displacements. To study the effects of design assumptions on the required number of cables, several manual calculations of the example in the Caltrans Restrainer design guidelines were carried out. The deviations from the method included the treatment of mass and stiffness of bridge segments as different hinges closed. Another variable was the simultaneous reduction in the Restrainer gap and increase in the hinge gap. The results indicated that slight variation in some of the assumptions can change the number of Restrainers significantly. A more streamlined design method that incorporates the nonlinear response of bridge components needs to be developed (Abstract by authors)
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Response of Bridge Hinge Restrainers during Earthquakes -Field Performance, Analysis, and Design
9999Co-Authors: Saiidi, Mehdi S., Maragakis, Emmanuel M., Feng Shiping, Abdel-ghaffar, Saber M., O'connor DanAbstract:Report No. CCEER-93-6This report presents a summary of the important findings of a study aimed at several aspects of the behavior of hinge Restrainers used as a seismic retrofit measure. Details of the study are described in five other reports [15 to 19]. The study included field investigations, extensive analytical studies, and an evaluation of the Restrainer design method. The objectives of the study were: To review the actual performance of bridge hinge Restrainers during the 1989 Loma Prieta earthquake To simulate the earthquake effect on the analytical models of several selected bridges and study their responses To carry out a parametric study of these bridges to determine the effect of stronger earthquakes and the effect of changes in the Restrainer gaps To review the Restrainer design procedure and recommend any needed refinements A data base of the bridges with hinge Restrainers which had been damaged by the 1989 ~Loma Prieta earthquake was formed. Twenty-three bridges were in the data base. The damage reports prepared by Caltrans maintenance Division were reviewed. Three bridges, namely, the Central Viaduct, the Route 580/24/980 Separation, and the Route 92/101 Separation were investigated in the field. Measurements were made of crack widths and patterns, and the condition of the Restrainers was examined. An analysis of locally damaged components was subsequently made. The field investigations pointed out the need to consider the performance of the Restrainer system and not merely the Restrainers. In addition to the Restrainers, the system includes (a) the connection between the Restrainers and the superstructure including any diaphragms, and (b) the superstructure adjacent to the hinge. The data base of the damaged bridges was also used to select four bridges for detailed nonlinear response history analyses using computer program NEABS-86. The four structures ranged from three to eleven spans. They had different number of hinges and different substructure characteristics. The earthquake intensity also varied considerably from one bridge to another. Two groups of earthquake analyses were carried out: in one analysis the input acceleration records collected at sites near the bridges were used, and in the other a series of parametric studies with larger peak ground acceleration (PGA) was conducted. The field investigations and the analyses showed that the Loma Prieta earthquake activated the hinge Restrainers in the majority of the bridges investigated in this study. Except for a few instances, the Restrainers and their supporting systems performed well. It was also noted that bridges with a small ratio of number of hinges to the number of spans and in which the substructure is relatively stiff, are less likely to be susceptible to support loss. The evaluation of the current Caltrans Restrainer design method consisted of two parts: (1) a study of the effect of refinement in the current methods, and (2) a large number of nonlinear analyses of the Caltrans example bridge for different earthquakes, hinge gaps, and the number of Restrainers. Based on these studies, a new method for the computation of the relative hinge movement was proposed, and demonstrated for one of the four bridges which had been the subject of detailed nonlinear analyses. It was found that the current Caltrans method for Restrainer design leads to a conservative and safe design in terms of the number of Restrainers. However, the degree of conservatism for different hinges is not uniform. It was also determined that a more refined method to compute relative hinge displacements can lead to fewer Restrainers even in hinges with a nominal seat width of 6 in. The refined method would explicitly incorporate the nonlinearity of soil at the footings and abutments, plastic hinging of the columns, and the nonlinearity of the hinges (Summary by authors)
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A Study of Fiber Reinforced Plastics for Seismic Bridge Restrainers
9999Co-Authors: Johnson Rita, Saiidi, Mehdi S., Maragakis, Emmanuel M.Abstract:Report No. CCEER-05-2Abstract: Easily installed and inspected fiber reinforced plastic (FRP) as an alternative to steel for Restrainer construction to reduce bridge hinge movements during earthquakes was examined. Glass, carbon, and hybrid (glass/carbon) Restrainers were constructed and dynamically tested in the large-scale structures laboratory. Work included: 1. Tensile tests on FRP strips and on FRP/concrete bond versus loading rate 2. FRP Restrainer development, including dynamic testing 3. Shake table data analysis and comparisons of FRP, steel, and SMA Restrainer performance 4. Development of a FRP Restrainer design method. Findings confirm FRP Restrainer potential for future implementation to structures Results include: 1. FRP strength is strain-rate insensitive 2. FRP/concrete bond strength is a function of concrete shear strength and is strain rate sensitive 3. Flexible Restrainer construction and Restrainer/concrete bond methods are demonstrated 4. A simplified FRP Restrainer design method, more realistic than AASHTO, and that considers bridge structure dynamic characteristics, is propose
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Experimental Evaluation of Seismic Performance of SMA Bridge Restrainers
9999Co-Authors: Johnson Rita, Saiidi, Mehdi S., Maragakis, Emmanuel M., Desroches ReginaldAbstract:Report No. CCEER-04-2Tests were conducted at the University of Nevada Reno Large Structures Laboratory, in cooperation with Georgia Institute of Technology, to determine the effect of shape memory alloy (SMA) cable and rod Restrainers on the seismic performance of in-span hinges of a representative multiple-frame concrete box girder bridge subjected to earthquake excitation. Another objective of this study was to compare the performance of SMA to steel Restrainers as restraining devices to reduce hinge displacement. Data collected from SMA Restrainer experiments was compared to information gathered in a previous University of Nevada, Reno study on the performance of steel Restrainers. The SMA Restrainers showed promise as restraining devices to limit hinge displacement in bridges and the ability to dissipate energy. Under equivalent loading, the steel Restrainers produced relative hinge displacement approximately three to four times that of the SMA Restrainers. The hysteretic damping that was seen in the larger ground accelerations showed the materials ability to dissipate energy with small residual strain
Shumin Feng - One of the best experts on this subject based on the ideXlab platform.
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parameters in bridge Restrainer design for seismic retrofit
Journal of Structural Engineering-asce, 1996Co-Authors: Mehdi S Saiidi, Emmanuel A Maragakis, Shumin FengAbstract:The primary objective of this study was to determine the effects of changing (1) the cross-sectional area of Restrainers; and (2) the Restrainer gap on the nonlinear seismic response of a representative bridge with several hinges. The computer program NEABS-86 was used in the nonlinear analyses. The focus of the study was the relative displacements at the hinges, Restrainer stresses, and abutment forces. The input earthquake, the number of Restrainers at each hinge, the Restrainer gap, and the hinge gap were varied. It was found that Restrainer forces can become critical in cold weather, when the Restrainer gap is minimum. It is recommended that the design should be based on cases with and without Restrainer gaps to encompass all the critical forces, stresses, and displacements.
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EVALUATION OF THE CURRENT CALTRANS SEISMIC Restrainer DESIGN METHOD
1992Co-Authors: Mehdi S Saiidi, Emmanuel A Maragakis, Shumin FengAbstract:The focus of this study was to understand the implications of the current Calif. Department of Transportation (Caltrans) hinge Restrainer design procedure. Two aspects were studied. One was the effects of changing the cross sectional area of Restrainers and the Restrainer gap on the nonlinear response of a bridge with several hinges. The second was the sensitivity of the number of required Restrainers to changes in some of the simplifying assumptions which are made in the current Caltrans Restrainer design method. The focus of the nonlinear analyses was the relative displacements at the joints, Restrainer forces, and Restrainer stresses. The level of ductility demand in the piers was also examined to identify the extent of nonlinearity. Different earthquake records were used for insuring that conclusions reflect the effects of a variety of ground excitations. In addition to the input earthquake, the number of Restrainers at each hinge, the Restrainer gap, and the hinge gap were also varied. Only longitudinal bridge response was considered to be consistent with the design method. In order to study the effects of design assumptions on the required number of cables, several manual calculations of the design example in the Caltrans Restrainer design guidelines were carried out. The deviations from the method included a different treatment of mass and stiffness as different hinges closed as a result of the earthquakes. Another variable was the simultaneous change in the Restrainer and the hinge gaps.
Reginald Desroches - One of the best experts on this subject based on the ideXlab platform.
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large scale testing of nitinol shape memory alloy devices for retrofitting of bridges
Smart Materials and Structures, 2008Co-Authors: Rita Johnson, Reginald Desroches, Jamie E Padgett, Emmanuel M Maragakis, Saiid M SaiidiAbstract:A large scale testing program was conducted to determine the effects of shape memory alloy (SMA) Restrainer cables on the seismic performance of in-span hinges of a representative multiple-frame concrete box girder bridge subjected to earthquake excitations. Another objective of the study was to compare the performance of SMA Restrainers to that of traditional steel Restrainers as restraining devices for reducing hinge displacement and the likelihood of collapse during earthquakes. The results of the tests show that SMA Restrainers performed very well as restraining devices. The forces in the SMA and steel Restrainers were comparable. However, the SMA Restrainer cables had minimal residual strain after repeated loading and exhibited the ability to undergo many cycles with little strength and stiffness degradation. In addition, the hysteretic damping that was observed in the larger ground accelerations demonstrated the ability of the materials to dissipate energy. An analytical study was conducted to assess the anticipated seismic response of the test setup and evaluate the accuracy of the analytical model. The results of the analytical simulation illustrate that the analytical model was able to match the responses from the experimental tests, including peak stresses, strains, forces, and hinge openings.
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full scale tests of seismic cable Restrainer retrofits for simply supported bridges
Journal of Bridge Engineering, 2003Co-Authors: Reginald Desroches, Thomas Pfeifer, Roberto T Leon, Tam LamAbstract:Many parts of the central and southeastern United States have recently begun initiating seismic retrofit programs for bridges on major interstate highways. One of the most common retrofit strategies is to provide cable Restrainers at the intermediate hinges and abutments in order to reduce the likelihood of collapse due to unseating. To evaluate the force-displacement behavior of the cable Restrainer retrofits, a full-scale bridge setup was constructed based on an existing multispan, simply supported steel girder bridge in Tennessee, that has been considered for seismic retrofit using cable Restrainers. Seismic cable Restrainers were connected to the bridge pier using steel bent plates, angles, and undercut anchors embedded in the concrete as specified by typical bridge retrofit plans. The full-scale bridge model was subjected to monotonic loading to test the capacity of the cable Restrainer system and to determine the modes of failure. The results showed that the primary modes of failure are in the connection elements of the pier and girders, and they occur at force levels much lower than the strength of the cable. Modifications to the connection elements were designed and tested. The new connections resulted in a higher strength and deformation capacity of the cable Restrainer assembly.
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seismic retrofit of simply supported bridges using shape memory alloys
Engineering Structures, 2002Co-Authors: Reginald Desroches, M DelemontAbstract:Recent earthquakes in the United States and Japan have highlighted the vulnerability of bridges to collapse due to excessive movement at the intermediate hinges and abutments. This study investigates the effectiveness of shape memory alloy Restrainer bars to reduce the seismic vulnerability of bridges. Full-scale tests of shape memory alloy (SMA) Restrainer bars are conducted to determine their force-deformation and energy dissipation characteristics. The 25.4 mm diameter bars are subjected to cyclical strains up to 8%, with minimum residual deformation. The effectiveness of the SMA Restrainer bars in bridges is assessed through nonlinear analyses of a typical multi-span simply supported bridge. The SMA Restrainer bars are effective in limiting the relative displacement at the piers and abutments. In addition, the bars are shown to be very effective for near-field ground motion.
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simplified Restrainer design procedure for multiple frame bridges
Earthquake Spectra, 2001Co-Authors: Reginald Desroches, Gregory L FenvesAbstract:The collapse of existing bridges due to unseating at supports and intermediate (in-span) hinges with inadequate seat-width can be prevented by the use of Restrainers to limit the relative hinge opening. A new simplified procedure for the design of Restrainers in bridges accounts for the dynamic characteristics and out-of-phase motion of adjacent frames as well as the inelastic behavior of the bridge. The simplified procedure is developed from an empirical relationship for the Restrainer stiffness as a function of the frame stiffnesses, initial hinge displacement, target displacement, and target ductility of the structure. Parameter studies and case studies show that the simplified procedure limits the relative hinge displacement to a designer-specified value.
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Seismic mitigation of bridges using smart Restrainers
Smart Structures and Materials 1999: Smart Systems for Bridges Structures and Highways, 1999Co-Authors: Reginald DesrochesAbstract:Recent earthquakes in the US and Japan have highlighted the vulnerability of bridges to collapse due to excessive movement at the hinges as a result of bearing and Restrainer failure. Conventional hinge Restrainers used in the US and Japan do not provide adequate protection from unseating, which can lead to collapse of bridges. This paper investigates the efficacy of using 'smart Restrainers' to reduce the seismic vulnerability of bridges. The use of shape memory alloy devices as replacements for conventional Restrainers are investigated as a method of improving the seismic response of bridges. Analytical studies show that these deices, used as passive dampers, are effective in both limiting the relative displacement between frames, and reducing the negative effects of pounding of bridge decks. In addition, by concentrating damage and energy dissipation in controlled locations, these devices can be used to reduce the demand on individual frames in multiple-frame bridges. Comparisons with conventional Restrainers show that the 'smart Restrainers' are more effective for a wide range of ground motions and bridge types than current Restrainers.
Saiidi, Mehdi S. - One of the best experts on this subject based on the ideXlab platform.
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Effects of Hinge Restrainers on the Response of the San Gregorio Bridge during the Loma Prieta Earthquake
9999Co-Authors: Maragakis, Emmanuel M., Saiidi, Mehdi S., Feng Shiping, Flournoy LindaAbstract:Report No. CCEER-93-5The primary objective of this study is to study the effects of cable Restrainers on the nonlinear seismic response of the San Gregorio Bridge. The computer program NEABS-86 was used in the nonlinear analyses. The earthquake analyses focus on the relative displacements at the hinges, the Restrainer stresses, and the abutment forces in both the longitudinal and the transverse directions of the bridge. The peak ground acceleration of the earthquake input, the seismic retrofit, the Restrainer gap, and the hinge gap were varied. It was found that, in general, the cable Restrainer system reduces the hinge responses in both the longitudinal and the transverse directions. Also found was that, when a zero Restrainer gap is assumed, the hinge responses change significantly. It is recommended that the Restrainer design be based on cases with both zero and non-zero Restrainer gaps, to encompass all the critical forces, stresses and displacements. Finally, some design methods for the longitudinal Restrainer cable at intermediate hinges of the bridge were evaluated. A modified "Dynamic-Caltrans" design procedure was tested preliminarily, and showed some promising results (Abstract by authors)
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An Evaluation of the Current Caltrans Seismic Restrainer Design Method
9999Co-Authors: Saiidi, Mehdi S., Maragakis, Emmanuel M., Feng ShipingAbstract:Report No. CCEER-92-8The primary objective of this study was to develop an understanding of the implications of the current Caltrans hinge Restrainer design procedure. Two aspects of the problem were studied. One was the effects of changing (a) the cross sectional area of Restrainers and (b) the Restrainer gap on the nonlinear response of a bridge with several hinges. The other was the sensitivity of the number of required Restrainers to changes in some of the simplifying assumptions which are made in the current Caltrans Restrainer design method. Computer program NEABS-86 was used in the nonlinear analyses [3]. The focus of this part of the study was the relative displacements at the joints, Restrainer forces, and Restrainer stresses. Three earthquake records, the El Centro 1940, Eureka 1954, and Saratoga 1989. In addition to input earthquakes, the number of Restrainers at each hinge, the Restrainer gaps, and the hinge gaps were varied. It was found that when a Restrainer gap of 0.75 in. is assumed, the number of Restrainers does not affect the response significantly. It is recommended that the design should be based on cases with and without Restrainer gaps to encompass all the critical forces, stresses, and displacements. To study the effects of design assumptions on the required number of cables, several manual calculations of the example in the Caltrans Restrainer design guidelines were carried out. The deviations from the method included the treatment of mass and stiffness of bridge segments as different hinges closed. Another variable was the simultaneous reduction in the Restrainer gap and increase in the hinge gap. The results indicated that slight variation in some of the assumptions can change the number of Restrainers significantly. A more streamlined design method that incorporates the nonlinear response of bridge components needs to be developed (Abstract by authors)
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Response of Bridge Hinge Restrainers during Earthquakes -Field Performance, Analysis, and Design
9999Co-Authors: Saiidi, Mehdi S., Maragakis, Emmanuel M., Feng Shiping, Abdel-ghaffar, Saber M., O'connor DanAbstract:Report No. CCEER-93-6This report presents a summary of the important findings of a study aimed at several aspects of the behavior of hinge Restrainers used as a seismic retrofit measure. Details of the study are described in five other reports [15 to 19]. The study included field investigations, extensive analytical studies, and an evaluation of the Restrainer design method. The objectives of the study were: To review the actual performance of bridge hinge Restrainers during the 1989 Loma Prieta earthquake To simulate the earthquake effect on the analytical models of several selected bridges and study their responses To carry out a parametric study of these bridges to determine the effect of stronger earthquakes and the effect of changes in the Restrainer gaps To review the Restrainer design procedure and recommend any needed refinements A data base of the bridges with hinge Restrainers which had been damaged by the 1989 ~Loma Prieta earthquake was formed. Twenty-three bridges were in the data base. The damage reports prepared by Caltrans maintenance Division were reviewed. Three bridges, namely, the Central Viaduct, the Route 580/24/980 Separation, and the Route 92/101 Separation were investigated in the field. Measurements were made of crack widths and patterns, and the condition of the Restrainers was examined. An analysis of locally damaged components was subsequently made. The field investigations pointed out the need to consider the performance of the Restrainer system and not merely the Restrainers. In addition to the Restrainers, the system includes (a) the connection between the Restrainers and the superstructure including any diaphragms, and (b) the superstructure adjacent to the hinge. The data base of the damaged bridges was also used to select four bridges for detailed nonlinear response history analyses using computer program NEABS-86. The four structures ranged from three to eleven spans. They had different number of hinges and different substructure characteristics. The earthquake intensity also varied considerably from one bridge to another. Two groups of earthquake analyses were carried out: in one analysis the input acceleration records collected at sites near the bridges were used, and in the other a series of parametric studies with larger peak ground acceleration (PGA) was conducted. The field investigations and the analyses showed that the Loma Prieta earthquake activated the hinge Restrainers in the majority of the bridges investigated in this study. Except for a few instances, the Restrainers and their supporting systems performed well. It was also noted that bridges with a small ratio of number of hinges to the number of spans and in which the substructure is relatively stiff, are less likely to be susceptible to support loss. The evaluation of the current Caltrans Restrainer design method consisted of two parts: (1) a study of the effect of refinement in the current methods, and (2) a large number of nonlinear analyses of the Caltrans example bridge for different earthquakes, hinge gaps, and the number of Restrainers. Based on these studies, a new method for the computation of the relative hinge movement was proposed, and demonstrated for one of the four bridges which had been the subject of detailed nonlinear analyses. It was found that the current Caltrans method for Restrainer design leads to a conservative and safe design in terms of the number of Restrainers. However, the degree of conservatism for different hinges is not uniform. It was also determined that a more refined method to compute relative hinge displacements can lead to fewer Restrainers even in hinges with a nominal seat width of 6 in. The refined method would explicitly incorporate the nonlinearity of soil at the footings and abutments, plastic hinging of the columns, and the nonlinearity of the hinges (Summary by authors)
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A Study of Fiber Reinforced Plastics for Seismic Bridge Restrainers
9999Co-Authors: Johnson Rita, Saiidi, Mehdi S., Maragakis, Emmanuel M.Abstract:Report No. CCEER-05-2Abstract: Easily installed and inspected fiber reinforced plastic (FRP) as an alternative to steel for Restrainer construction to reduce bridge hinge movements during earthquakes was examined. Glass, carbon, and hybrid (glass/carbon) Restrainers were constructed and dynamically tested in the large-scale structures laboratory. Work included: 1. Tensile tests on FRP strips and on FRP/concrete bond versus loading rate 2. FRP Restrainer development, including dynamic testing 3. Shake table data analysis and comparisons of FRP, steel, and SMA Restrainer performance 4. Development of a FRP Restrainer design method. Findings confirm FRP Restrainer potential for future implementation to structures Results include: 1. FRP strength is strain-rate insensitive 2. FRP/concrete bond strength is a function of concrete shear strength and is strain rate sensitive 3. Flexible Restrainer construction and Restrainer/concrete bond methods are demonstrated 4. A simplified FRP Restrainer design method, more realistic than AASHTO, and that considers bridge structure dynamic characteristics, is propose
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Experimental Evaluation of Seismic Performance of SMA Bridge Restrainers
9999Co-Authors: Johnson Rita, Saiidi, Mehdi S., Maragakis, Emmanuel M., Desroches ReginaldAbstract:Report No. CCEER-04-2Tests were conducted at the University of Nevada Reno Large Structures Laboratory, in cooperation with Georgia Institute of Technology, to determine the effect of shape memory alloy (SMA) cable and rod Restrainers on the seismic performance of in-span hinges of a representative multiple-frame concrete box girder bridge subjected to earthquake excitation. Another objective of this study was to compare the performance of SMA to steel Restrainers as restraining devices to reduce hinge displacement. Data collected from SMA Restrainer experiments was compared to information gathered in a previous University of Nevada, Reno study on the performance of steel Restrainers. The SMA Restrainers showed promise as restraining devices to limit hinge displacement in bridges and the ability to dissipate energy. Under equivalent loading, the steel Restrainers produced relative hinge displacement approximately three to four times that of the SMA Restrainers. The hysteretic damping that was seen in the larger ground accelerations showed the materials ability to dissipate energy with small residual strain
Rita Johnson - One of the best experts on this subject based on the ideXlab platform.
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large scale testing of nitinol shape memory alloy devices for retrofitting of bridges
Smart Materials and Structures, 2008Co-Authors: Rita Johnson, Reginald Desroches, Jamie E Padgett, Emmanuel M Maragakis, Saiid M SaiidiAbstract:A large scale testing program was conducted to determine the effects of shape memory alloy (SMA) Restrainer cables on the seismic performance of in-span hinges of a representative multiple-frame concrete box girder bridge subjected to earthquake excitations. Another objective of the study was to compare the performance of SMA Restrainers to that of traditional steel Restrainers as restraining devices for reducing hinge displacement and the likelihood of collapse during earthquakes. The results of the tests show that SMA Restrainers performed very well as restraining devices. The forces in the SMA and steel Restrainers were comparable. However, the SMA Restrainer cables had minimal residual strain after repeated loading and exhibited the ability to undergo many cycles with little strength and stiffness degradation. In addition, the hysteretic damping that was observed in the larger ground accelerations demonstrated the ability of the materials to dissipate energy. An analytical study was conducted to assess the anticipated seismic response of the test setup and evaluate the accuracy of the analytical model. The results of the analytical simulation illustrate that the analytical model was able to match the responses from the experimental tests, including peak stresses, strains, forces, and hinge openings.
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Development, Shake Table Testing, and Design of FRP Seismic Restrainers
Journal of Bridge Engineering, 2006Co-Authors: M Saiid Saiidi, Rita Johnson, E. “manos” MaragakisAbstract:The development and performance of fiber-reinforced polymer (FRP) fabrics as an alternative to steel for Restrainers to reduce bridge relative movements at hinges during earthquakes was explored. Glass, carbon, and hybrid (glass/carbon) Restrainers were developed and tested on a representative in-span hinge using a shake table at the large-scale structures laboratory at the University of Nevada, Reno. The components of the study presented in this article are: (1) the FRP Restrainer development and testing; (2) comparisons among FRP, steel, and shape memory alloy Restrainers; and (3) development and evaluation of a simple Restrainer design method and a numerical example. Important findings of the study were that compared to steel Restrainers, the FRP Restrainers were effective in substantially reducing the relative hinge displacements and pounding at hinges. The method to develop the flexible portion of the FRP Restrainers and the bond to superstructure was successful in accomplishing the target performance. The proposed Restrainer design method provides a rational yet simple tool to design FRP or other types of Restrainers.
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A Study of Fiber Reinforced Plastics for Seismic Bridge Restrainers
NCHRP-IDEA Program Project Final Report, 2005Co-Authors: Rita Johnson, M Saiid Saiidi, M MaragakisAbstract:This Innovations Deserving Exploratory Analysis (IDEA) project evaluated the use of fiber-reinforced plastic (FRP) fabrics as Restrainers for seismic rehabilitation of highway bridges as an alternative to steel Restrainers to reduce bridge hinge movement during earthquakes. Glass, carbon, and glass/carbon hybrid Restrainers were fabricated and evaluated in large-scale dynamic laboratory tests. The research work involved (i) tensile tests on FRP strips and on FRP/concrete bond at various loading rates, (ii) FRP Restrainer development and dynamic testing, (iii) shake table tests, data analysis, and performance comparison for FRP, steel, and shape memory alloy (SMA) Restrainers, and (iv) development of a FRP Restrainer design method. The results showed that the FRP strength was insensitive to strain rates and that the FRP/concrete bond was a function of concrete shear strength but insensitive to strain rates. The results also demonstrated feasible methods for flexible Restrainer construction and Restrainer/concrete bonding. A simplified FRP Restrainer design method, considered more realistic than that of AASHTO was proposed that takes into account the dynamic characteristics of a bridge structure.