| Reinforced concrete shear walls are widely employed as the primary lateral load resisting members in high-rise and super-high-rise buildings in earthquake-prone regions,which undertake most of the earthquake action of the buildings.Therefore,the mechanical properties of shear wall are particularly important to the seismic performance of the whole building structure.The traditional seismic design philosophy is to improve the stiffness and strength of the component itself.However,the problems of large residual deformation and macro cracks under strong earthquake are still unable to be addressed.In recent years,smart materials such as the shape memory alloy(SMA)provide a new way for the self-recentering system.High ductility engineering cementitious composites(ECC)could address the issue of the fragility of concrete.A complementary and synergistic material system that integrates SMA and ECC not only has good energy dissipation capacity,but also has superior self restoration performance,so as to improve the seismic performace and durability of the structure.In this paper,a novel self-recentering SMA-ECC shear wall was proposed,in which the longitudinal steel bars in the plastic hinge region of the boundary area were replaced by SMA and the concrete in the plastic deformation area of the wall was replaced by ECC.The tensile test of the mechanical properties of the materials and the low cyclic experiment of the SMA-ECC shear wall were carried out.The finite element analysis model of the SMA-ECC shear wall was established and the parameter optimization analysis was performed.The calculation method of the SMA-ECC shear wall was proposed.The dynamic time history analysis of the shear wall structure was conducted.The major research contents are as follows:(1)The mechanical properties of the shape memory alloy bars with different diameters and PVA-ECC sheets were experimentally investigated.The effects of the heat-treatment strategies,cyclic loading-unloading times and strain amplitudes on the mechanical properties of SMA were discussed by uniaxial tension,and the tensile properties of ECC materials were analyzed.The test results indicate that the superelastic property of SMA can be improved by heat treatment.At a certain temperature,the recovery stress plateau decreases with the increase of annealing duration.The cyclic loading and unloading training is conducive to the stability of various properties of SMA.The increase of strain amplitude will affect mechanical properties of the material.The material of ECC presents pseudo-strain hardening characteristics,with ultimate tensile strains over 2.5%.(2)The seismic performance of the SMA-ECC shear wall was studied by quasi-static test.The scaled SMA-ECC shear wall and the SMA-C shear wall,the reinforced ECC shear wall and the oridinary RC shear wall were designed and constructed.The bearing capacity,failure mode,energy dissipation capacity,displacement ductility and self-certering capacity of the shear walls were compared and studied by quasi-static test.The test results indicate that the SMA-ECC shear wall not only has good ductility and energy dissipation capacity,but also has superior self-centering ability and the recoverable deformation can reach more than 85%,compared with other shear walls.The damage has been reduced and the durability and the seismic performance of the components have been greatly improved.(3)The nonlinear finite element analysis model of the SMA-ECC shear wall was established.The shell element model,the fiber beam-column element model and multi-vertical rod element model of the SMA-ECC shear wall were established from both the micro and macro perspectives based on the finite-element program OpenSees.The numerical analyses were carried out by cyclic loading protocol.The analysis results show that the numerical results are in good agreement with the experimental results,which verifies the accuracy of the finite element model.The fiber model can better simulate the self-centering and hysteretic performance of the SMA-ECC shear wall compared with the other two models.(4)The optimization analysis of seismic performance parameters of the SMA-ECC shear wall was performed.The influences of axial load ratio,shear span ratio,the yield strength and the reinforcement ratio of SMA,the tensile strength and ultimate tensile strain of ECC on the seismic performance of the new shear wall were studied,and the optimization analysis was carried out.The analysis results show that a better self-recentering performance of the component will be appeared with a high shear-span ratio and a certain axial load ratio;the shear wall exhibits the best self-recentering effect with appropriate reinforcement of SMA;the ductility and deformation capacity of the component can be improved by increasing the tensile strength and ultimate tensile strain of ECC.(5)The flexural behavior of the SMA-ECC shear wall was analyzed theoretically.The calculation methods of flexural cracking load,yield load and peak load of the SMA-ECC shear wall were proposed and compared with the experimental data based on the constitutive relationship of SMA and ECC materials.The results show that the calculation results of the proposed formula are in good agreement with the experimental results,which verifies the accuracy of the calculation method.(6)The nonlinear time history analysis of the SMA-ECC shear wall structure was carried out.The finite element model of a nine story SMA-ECC shear wall structure was established.The time history analysis of shear wall structure under different ground motions is carried out.The residual displacements,story drift ratio and the overall displacement of the structure were analyzed.The seismic performance and self-centering ability of the new type of shear wall structure were studied and analyzed.The results show that the SMA-ECC shear wall structure can basically restored to its original position after strong earthquake,and the residual displacement is reduced by more than 80%compared with the ordinary reinforced concrete structure.It shows superior self-recentering performance. |
