A 15-storey K-braced reinforced concrete model frame with irregular columns, i.e., T-shaped, L-shaped, as well as ＋-shaped columns, was constructed and tested on the six-degree-of-freedom shaking table at the State K...A 15-storey K-braced reinforced concrete model frame with irregular columns, i.e., T-shaped, L-shaped, as well as ＋-shaped columns, was constructed and tested on the six-degree-of-freedom shaking table at the State Key Laboratory for Disaster Reduction in Civil Engineering in Tongji, China. Two types of earthquake records, El-Centro wave （south-north direction） and Shanghai artificial wave （SHAW） with various peak accelerations and principal-secondary sequences, were input and experimentally studied. Based on the shaking table tests and theoretical analysis, several observations can be made. The failure sequence of the model structure is brace→beam→column→joints, so that the design philosophy for several lines of defense has been achieved. Earthquake waves with different spectrums not only influence the magnitude and distribution of the earthquake force and the storey shear force, but also obviously affect the magnitude of the displacement response. The aftershock seismic response of previously damaged reinforced concrete braced frames with irregular columns possesses the equivalent elastic performance characteristic. Generally speaking, from the aspects of failure features and drift ratio, this type of reinforced concrete structure provides adequate earthquake resistance and can be promoted for use in China.展开更多
This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace, termed glass-fiber-reinforced-polymer （GFRP）-tube-confined-concrete comp...This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace, termed glass-fiber-reinforced-polymer （GFRP）-tube-confined-concrete composite brace, is comprised of concrete confined by a GFRP tube and an inner steel core for energy dissipation. Together with a contribution from the GFRP-tube confined concrete, the composite brace shows a substantially increased stiffness to control story drift, which is often a preferred feature in seismic retrofitting. An analysis model is established and implemented in a general finite element analysis program - OpenSees, for simulating the load-displacement behavior of the composite brace. Using this model, a parametric study of the hysteretic behavior （energy dissipation, stiffness, ductility and strength） of the composite brace was conducted under static cyclic loading and it was found that the area ratio of steel core to concrete has the greatest influence among all the parameters considered. To demonstrate the application of the composite brace in seismic retrofitting, a three-story nonductile reinforced concrete （RC） frame structure was retrofitted with the composite braces. Pushover analysis and nonlinear time-history analyses of the retrofitted RC frame structure was performed by employing a suite of 20 strong ground motion earthquake records. The analysis results show that the composite braces can effectively reduce the peak seismic responses of the RC frame structure without significantly increasing the base shear demand.展开更多
The present work discusses the outcomes of recent experimental tests and numerical simulations carried out on full scale reinforced concrete （RC） non-ductile frames retrofitted with dissipative steel braces, i.e. in...The present work discusses the outcomes of recent experimental tests and numerical simulations carried out on full scale reinforced concrete （RC） non-ductile frames retrofitted with dissipative steel braces, i.e. innovative buckling restrained braces （BRBs）. Experimental tests were performed on two sample full scale RC framed buildings designed for gravity loads only. Such frames were subjected to cyclic pushovers to investigate their structural performance under different levels of earthquake loadings. The outcomes of the performed experimental tests demonstrate the efficiency and reliability of utilizing BRBs to retrofit non ductile RC frames. These outcomes were confirmed by refined non linear static and response history analyses carried out on an existing RC school framed building designed without seismic details and retrofitted with BRBs similar to those adopted for the tested full-scale frame. In such sample building the BRBs are placed along the perimeter of the existing frames to minimize the interruption of the functionality of the school and for easy of maintenance in the aftermath of major earthquake ground motions. The seismic performance assessment of the retrofitted structural system is illustrated in a detailed manner. Local and global response quantities are presented. The values of the global overstrength Ω for the case study vary between 2.14 and 2.54 for the retrofitted framed building. The translation ductility μ△-values range between 2.07 and 2.36. The response modification factor （or behaviour factor, namely R- or q-factor） is on average equal to 5.0. Additionally, the estimated maximum axial ductility of the BRBs is about 10. Finally, the cost-effectiveness of the adopted retrofitting scheme is emphasized and further needs for the application of BRBs are highlighted.展开更多
In this study, four 1/5 scaled shaking table tests were conducted to investigate the seismic performance of recycled concrete frame-shear wall structures with different recycled aggregates replacement rates and concea...In this study, four 1/5 scaled shaking table tests were conducted to investigate the seismic performance of recycled concrete frame-shear wall structures with different recycled aggregates replacement rates and concealed bracing detail. The four tested structures included one normal concrete model, one recycled coarse aggregate concrete model, and two recycled coarse and fi ne aggregate concrete models with or without concealed bracings inside the shear walls. The dynamic characteristics, dynamic response and failure mode of each model were compared and analyzed. Finite element models were also developed and nonlinear time-history response analysis was conducted. The test and analysis results show that the seismic performance of the recycled coarse aggregate concrete frame-shear wall structure is slightly worse than the normal concrete structure. The seismic resistance capacity of the recycled concrete frame-shear wall structure can be greatly improved by setting up concealed bracings inside the walls. With appropriate design, the recycled coarse aggregate concrete frame-shear wall structure and recycled concrete structure with concealed bracings inside the walls can be applied in buildings.展开更多
Shaking table tests of a 1:10 scale arch model performed to investigate the seismic behavior and resistance of concrete filled steel tubular (CFT) arch structures are described in this paper. The El-Centro record and ...Shaking table tests of a 1:10 scale arch model performed to investigate the seismic behavior and resistance of concrete filled steel tubular (CFT) arch structures are described in this paper. The El-Centro record and Shanghai artificial wave were adopted as the input excitation. The entire test process can be divided into three stages depending on the lateral brace configurations, i.e., fully (five) braced, two braces removed, and all braces removed. A total of 46 tests, starting from the elastic state to failure condition, have been conducted. The natural vibration frequencies, responses of acceleration, displacement and strain were measured. From the test results, it is demonstrated that the CFT arch structures are capable of resisting severe ground motions and that CFT arches offer a credible alternative to reinforced concrete arches, especially in regions of high seismic intensity.展开更多
The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can r...The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can release the compressive force in the bracing members is developed, and its performance is evaluated. For comparison, four steel braced RC frames were constructed and tested under reverse cyclic loads. Two of them had different amounts of bracing and the other two had the same amount of bracing but incorporated different type of device, called compression release device, which is developed and described in this paper. It can be concluded from the test results that the newly developed device can effectively be used in steel braced systems to prevent buckling failure of the bracing members. Therefore, the device enhances the ductility of brace-framed systems by allowing an adequate capacity for energy dissipation.展开更多
文摘A 15-storey K-braced reinforced concrete model frame with irregular columns, i.e., T-shaped, L-shaped, as well as ＋-shaped columns, was constructed and tested on the six-degree-of-freedom shaking table at the State Key Laboratory for Disaster Reduction in Civil Engineering in Tongji, China. Two types of earthquake records, El-Centro wave （south-north direction） and Shanghai artificial wave （SHAW） with various peak accelerations and principal-secondary sequences, were input and experimentally studied. Based on the shaking table tests and theoretical analysis, several observations can be made. The failure sequence of the model structure is brace→beam→column→joints, so that the design philosophy for several lines of defense has been achieved. Earthquake waves with different spectrums not only influence the magnitude and distribution of the earthquake force and the storey shear force, but also obviously affect the magnitude of the displacement response. The aftershock seismic response of previously damaged reinforced concrete braced frames with irregular columns possesses the equivalent elastic performance characteristic. Generally speaking, from the aspects of failure features and drift ratio, this type of reinforced concrete structure provides adequate earthquake resistance and can be promoted for use in China.
文摘This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace, termed glass-fiber-reinforced-polymer （GFRP）-tube-confined-concrete composite brace, is comprised of concrete confined by a GFRP tube and an inner steel core for energy dissipation. Together with a contribution from the GFRP-tube confined concrete, the composite brace shows a substantially increased stiffness to control story drift, which is often a preferred feature in seismic retrofitting. An analysis model is established and implemented in a general finite element analysis program - OpenSees, for simulating the load-displacement behavior of the composite brace. Using this model, a parametric study of the hysteretic behavior （energy dissipation, stiffness, ductility and strength） of the composite brace was conducted under static cyclic loading and it was found that the area ratio of steel core to concrete has the greatest influence among all the parameters considered. To demonstrate the application of the composite brace in seismic retrofitting, a three-story nonductile reinforced concrete （RC） frame structure was retrofitted with the composite braces. Pushover analysis and nonlinear time-history analyses of the retrofitted RC frame structure was performed by employing a suite of 20 strong ground motion earthquake records. The analysis results show that the composite braces can effectively reduce the peak seismic responses of the RC frame structure without significantly increasing the base shear demand.
文摘The present work discusses the outcomes of recent experimental tests and numerical simulations carried out on full scale reinforced concrete （RC） non-ductile frames retrofitted with dissipative steel braces, i.e. innovative buckling restrained braces （BRBs）. Experimental tests were performed on two sample full scale RC framed buildings designed for gravity loads only. Such frames were subjected to cyclic pushovers to investigate their structural performance under different levels of earthquake loadings. The outcomes of the performed experimental tests demonstrate the efficiency and reliability of utilizing BRBs to retrofit non ductile RC frames. These outcomes were confirmed by refined non linear static and response history analyses carried out on an existing RC school framed building designed without seismic details and retrofitted with BRBs similar to those adopted for the tested full-scale frame. In such sample building the BRBs are placed along the perimeter of the existing frames to minimize the interruption of the functionality of the school and for easy of maintenance in the aftermath of major earthquake ground motions. The seismic performance assessment of the retrofitted structural system is illustrated in a detailed manner. Local and global response quantities are presented. The values of the global overstrength Ω for the case study vary between 2.14 and 2.54 for the retrofitted framed building. The translation ductility μ△-values range between 2.07 and 2.36. The response modification factor （or behaviour factor, namely R- or q-factor） is on average equal to 5.0. Additionally, the estimated maximum axial ductility of the BRBs is about 10. Finally, the cost-effectiveness of the adopted retrofitting scheme is emphasized and further needs for the application of BRBs are highlighted.
基金National Science and Technology Support Program of China under Grant No.2011BAJ08B02Natural Science Foundation of Beijing under Grant No.8132016Beijing City University Youth Backbone Talent Training Project under Grant No.PHR201108009
文摘In this study, four 1/5 scaled shaking table tests were conducted to investigate the seismic performance of recycled concrete frame-shear wall structures with different recycled aggregates replacement rates and concealed bracing detail. The four tested structures included one normal concrete model, one recycled coarse aggregate concrete model, and two recycled coarse and fi ne aggregate concrete models with or without concealed bracings inside the shear walls. The dynamic characteristics, dynamic response and failure mode of each model were compared and analyzed. Finite element models were also developed and nonlinear time-history response analysis was conducted. The test and analysis results show that the seismic performance of the recycled coarse aggregate concrete frame-shear wall structure is slightly worse than the normal concrete structure. The seismic resistance capacity of the recycled concrete frame-shear wall structure can be greatly improved by setting up concealed bracings inside the walls. With appropriate design, the recycled coarse aggregate concrete frame-shear wall structure and recycled concrete structure with concealed bracings inside the walls can be applied in buildings.
基金This study was supported by the National Natural Science Foundation of China under Grant No.50078016Open Funding of State Key Laboratory for Disaster Reduction in Civil Engineering,China.
文摘Shaking table tests of a 1:10 scale arch model performed to investigate the seismic behavior and resistance of concrete filled steel tubular (CFT) arch structures are described in this paper. The El-Centro record and Shanghai artificial wave were adopted as the input excitation. The entire test process can be divided into three stages depending on the lateral brace configurations, i.e., fully (five) braced, two braces removed, and all braces removed. A total of 46 tests, starting from the elastic state to failure condition, have been conducted. The natural vibration frequencies, responses of acceleration, displacement and strain were measured. From the test results, it is demonstrated that the CFT arch structures are capable of resisting severe ground motions and that CFT arches offer a credible alternative to reinforced concrete arches, especially in regions of high seismic intensity.
文摘The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can release the compressive force in the bracing members is developed, and its performance is evaluated. For comparison, four steel braced RC frames were constructed and tested under reverse cyclic loads. Two of them had different amounts of bracing and the other two had the same amount of bracing but incorporated different type of device, called compression release device, which is developed and described in this paper. It can be concluded from the test results that the newly developed device can effectively be used in steel braced systems to prevent buckling failure of the bracing members. Therefore, the device enhances the ductility of brace-framed systems by allowing an adequate capacity for energy dissipation.
