| Recently, as one of the main structural forms of low-rise steel structure, cold-formed steel (CFS) structural system develops rapidly at home and abroad. It is a new structural system which originated from conventional timber structure and been made up of CFS framing and light sheathings. At present, CFS structure has the developing direction of higher strength but thinner thickness of CFS members and variety of sheathings, while extending the low-rise CFS structure to mid-rise building is an inevitable tendency. CFS shear walls are the main bearing components of CFS structural system, thus further researches on their mechanical performances have crucially theoretical value and practical significance. Based on the test researches on the axial compression and shear performance of CFS shear walls, a numerical simulation method of the mechanical performance of CFS shear walls was explored in this study, which is aimed at providing an analysis method for the research and design of CFS structure.CFS shear walls are the load bearing components of CFS structures. In this study, taking the axial compression test models as research objects, the axial compression performances of CFS shear walls are studied using the finite element method (FEM). Firstly, buckling analysis of CFS axial compressed column is carried out by ABAQUS finite element software and CUFSM finite strip software, it turned out that boundary condition is the key issue of the numerical simulation of CFS structure. After that, ABAQUS is used to simulate the axial compressed shear walls. Results indicate that utilizing nonlinear spring element to model the screw connection can consider the slipping deformation and failure, the ultimate loads and failure modes of the FEM results fit well with the test results.In the mid-rise CFS structure, CFS shear walls must meet the requirements of both fire resistance and shear resistance. Based on the shear test models of CFS shear walls, which either being sheathed with double-layer wallboards on both sides or using concrete-filled rectangular steel tube columns as end studs, FEM is used to study the performances of the walls. Firstly, researches on the shear performances of the walls under monotonic load are carried out by ABAQUS. Results show that using the coupling method to model the screw connection will over estimate the strength and stiffness of the walls, while using nonlinear spring element or connector element to model the screw connection is effective; the failure modes of the FEM results fit well with the test results, and the errors of ultimate loads are less than 10%. And then, the OpenSees finite element software is used to model the hysteretic behavior of the shear walls under cyclic load. The results indicate that Pinching4 material constitutive model can simulate the hysteretic characteristics of screw connection, and the hysteresis loops obtained from OpenSees present significant pinch effect, which agree well with the test results.Parameter analysis of the FEM results are carried out, the results indicate that:due to the different behaviors of the screw connections connecting with different wallboards, the mechanical performances of CFS shear walls sheathed with different wallboards show significant differences; the strength and stiffness of the walls sheathed with double-layer wallboards are approximately equal to the sum of the strength and stiffness of the walls sheathed with one-layer wallboards; increasing the width of the wall can improve the shear resistance, but there is no significant change in the strength per unit length; reducing stud space or increasing stud section can increase the shear strength within 10%; staggered configuration of the internal and external wallboards can improve the shear resistance of the wall, while it will weaken the ductility of the wall, battens between the internal and external wallboards can improve the shear strength too.The performances of shear walls with opening are studied by ABAQUS. Results show that both the strength and stiffness of the walls decrease with the increase of opening's area; studs on both sides of the opening have serious damages; the ductility of the walls with opening is better than the walls without opening; opening's position has no effect on the shear strength of the wall. The walls'strength calculated by different empirical formulas exist differences, compared with FEM results, the calculated results by empirical formulas are conservative, thus they can provide certain safety margin in practical design.In the seismic analysis of building, the walls must be simplified because the fine FEM models of shear walls will lead to computational difficulties. The equivalent diagonal bracing model in OpenSees is used to carried out the simplified analysis of shear walls, in which "twoNodeLink element" is used to model the diagonal bracing utilizing Pinching4 material constitutive model. The calculated results agree well with the test results, mean that the simplified model is correct and can provide basis for the seismic design of CFS structure. |
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