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This paper investigates the seismic behavior of a seismic-damaged double-deck viaduct frame pier (DVFP) strengthened with CFRP and enveloped steel, four strengthened DVFP specimens with different degrees of initial damage were tested under quasi-static cyclic loading. Based on the test results, the hysteretic behavior, the stiffness and strength degradation, crack propagation, and failure mechanism were firstly analyzed. Then, the damage indexes of the tested specimens were calculated with different models to evaluate the seismic strengthening performance. Results of this study show that CFRP and enveloped steel strengthening could effectively improve the strength and ductility of pre-damaged DVFPs. The ultimate load, the failure displacement and the displacement ductility of the moderately damaged specimen after being strengthened were found to increase by 120.74%, 35% and 32.33%, respectively. For the severely damaged specimens with CFRP and enveloped steel strengthening, the figures were 105.36%, 25.98% and 31.41%, respectively. The research results can provide reference for the hybrid strengthening application of seismic-damaged DVFP. [ABSTRACT FROM AUTHOR]

Four composite steel–concrete frame columns were constructed to investigate the seismic performance of seismic-damaged composite steel–concrete frame columns strengthened with carbon fiber reinforced polymer. The test consisted of pre-damage loading, rehabilitation with carbon fiber reinforced polymer and destruction tests under lateral cyclic loading. The effectiveness of strengthening seismic-damaged columns with carbon fiber reinforced polymer and the strengthening effect on different degrees of seismic damage were studied. Also, based on the test data, various parameters were obtained, including the hysteretic loops, skeleton curves, axial compression ratio, number of pasted layers of carbon fiber reinforced polymer, ductility, dissipative ability, ultimate strength, stiffness degradation, etc. The results revealed that the failure mode of all the columns was bending failure. The study indicates that the rehabilitated columns can reach or even exceed the level of their original seismic performance before seismic damage up to a certain extent of damage level. Composite steel–concrete frame columns strengthened with carbon fiber reinforced polymer sheets were simulated using the finite element analysis software ABAQUS. The comparison of the results of the conducted analytical study with the experimental results revealed that they are basically consistent with each other. [ABSTRACT FROM AUTHOR]

• Influence of damage degrees and confinement materials on seismic behavior of joints. • FE models of strengthened joints are calibrated with test results. • The predicted models of the shear capacity are good agreement with test results. • The results provide useful information for the engineering application. The seismic behavior of reinforced concrete (RC) beam-steel-reinforced concrete (SRC) column composite joints strengthened with carbon fiber-reinforced polymer (CFRP) sheets and enveloped steel jackets (ESJ) was investigated. Based on the existing regulations, nine specimens were designed and built to simulate pre-damage loading, rehabilitation with CFRP sheets or ESJ, and destruction tests under lateral cyclic loading to determine the performance of the two reinforcement materials (CFRP sheets and ESJ) for different degrees of seismic damage. An analysis of the hysteretic curves, skeleton curves, ductility, energy dissipation, bearing capacity degradation, stiffness degradation, and strain-displacement curves of the specimens indicated that the two strengthening materials exhibited good reinforcement performance. The ESJ improved the bearing capacity and stiffness of the specimens and the CFRP sheets improved the ductility and energy dissipation of the specimens, thereby improving the seismic behavior of the specimens. The severely damaged specimen strengthened with the CFRP sheets or ESJ did not collapse in a simulated strong earthquake and was similar to or even exceeded the seismic performance of the original specimen; this result is important and applicable to engineering practice. The ductility and energy dissipation was lower for the ESJ-strengthened specimen than the CFRP-strengthened specimen. Therefore, the ESJ material is preferable when only one type of material is used for strengthening the specimen. The seismic performance of the RC beam-SRC column frame joints strengthened with the CFRP sheets and ESJ was simulated using the finite element analysis software ABAQUS. There was a good agreement between the simulation results and the experimental results. It was proved that the simulated and experimental results of the ultimate bearing capacity of the joints in the core zones were in good agreement, which meets the design principle of "strong joint, weak member". [ABSTRACT FROM AUTHOR]

The combination of superelastic shape memory alloy fibers and ECC materials can form a new SMA fiber reinforced ECC composite material (SMAF-ECC) with good self-centering performance. In order to study the self-centering performance of the new composite material, 6 groups of pre-notch beam specimens were made for three-point bending cyclic loading tests, and the failure phenomenon, hysteresis curve, self-centering effect and influencing factors of the specimens were analyzed. The research results show that when the SMA fibers are effectively anchored in the ECC matrix, the SMA fibers can exert the superelastic properties to provide the ECC beams with recoverying force, and realize the crack self-closure and deflection self-recovery function for the beams, with the minimum residual crack width and deflection is only 0.9 mm and 1.3 mm respectively. Increasing fiber content can cause a small increase in the self-centering ability of the beams. However, only when the fiber diameter is appropriate, better self-centering effect can be achieved, but the difference caused by fiber diameter in the test was only 5%. SMA Fiber end forms have significant influence on self-centering performance. The knotted end beam can get a more than 70% self-centering ratio, while the straight end beams and bended end beams have no self-centering ability. The research results provide important reference for the research and application of this new self-centering materials and their structures. [ABSTRACT FROM AUTHOR]

This paper reports a study of the effects of different concealed bracing materials on the seismic performance of short-legged shear walls and presents the results of low-frequency cyclic loading tests on three L-shaped short-leg shear walls—one wall without concealed bracing and the other two with concealed bracing materials of steel bars and SMA bars, respectively. The tests were aimed mainly at analyzing the effects of different concealed bracing materials on seismic performance indicators such as crack pattern, bearing capacity, ductility, hysteresis performance, stiffness, and energy dissipation of the L-shaped short-leg shear walls. The results revealed that their seismic performance with concealed bracing was better than without concealed bracing. The short-leg shear walls with SMA bar concealed bracing had the lowest number of cracks and the smallest crack width, and the effect of delaying the development of cracks was more evident. The short-leg shear walls with steel reinforcement and SMA-bar concealed bracing were better in bearing capacity, ductility, and energy dissipation capacity, with, respectively, 11% and 26.3% increase in ultimate load, 4% and 18.6% increase in ultimate displacement, and 12% and 28% increase in energy dissipation. It can be seen that setting concealed bracing effectively enhances the seismic performance of short-leg shear walls, and that short-leg shear walls with concealed SMA bar bracing have the most significant improvement in seismic performance. • The low-frequency cyclic loading tests on three L-shaped short-leg shear walls with different concealed bracing materials were conducted. • The effects of different concealed bracing materials on seismic performance indicators of the L-shaped short-leg shear walls were explored. • The short-leg shear walls with concealed SMA bar bracing have the most significant improvement in seismic performance. [ABSTRACT FROM AUTHOR]