Research On Seismic Behavior Of Small Span-to-depth Ratio Coupling Beams Under Shear Wall Constraint

The coupling beams are important component for seismic energy dissipation in coupled shear wall in high-rise structures. The interaction between shear wall limbs and coupling beams makes the force state of coupling beams very complax. At present, researchers simplify the coupling beams into a bi-antisymmetric flexural members under horizontal earthquake, and the experiment of ductility capacity and ductility demand can not reflect the seismic performance. This paper is aimed at the coupling beams with span to depth ratio L/h≤1.5 and considering the factors of wall limb axial constraint, different wall scales, the vertical deformation of wall limb, the constraint of the slab, thus the main research content are:①On the basis of the strut-tie model of coupling beams without axial constraint, this paper set up the strut-tie model considering the axial constraint in the horizontal earthquake, through changing the main and secondary diagonal strut-tie model of the concret and the the geometric equations, the deformation coordinate equations, the physical conditions and the balance equations, this paper worked out the LL-Y program in order to analysis the coupling beams,and compare the result of the calculation and the experiment of the seismic performance in the macroscopic aspect and the microscopic aspect.②The seismic performance of unconstrained coupling beams with low span-depth ratios is in simulation analysis by the commercial finite element software ABAQUS. On the foundation of determination of the finite element type and the material constitutive model for this kind of coupling beams, 12 finite element analysis models of the coupled shear wall structure are built, including four different shear wall limb heights of 900 mm, 2400 mm, 3000 mm and 4500 mm, two span-depth ratios of 1.0 and 1.5, and three reinforcement ratios. Quantitative analysis of comprehensive seismic performance such as the stress and deformation and the redistribution of internal force characteristics as well as ductility capacity of composite reinforced coupling beams with low span-depth ratio are made under influence of multiple factors.③ Coupling beams with low span-depth ratios under unilateral constrains of castin –place slab is in finite element analysis. Influence of slabs on yield displacement, yield loads, ultimate loads and nominal shear compression ratio of coupling beams, and the change of effective width of slab longitudinal reinforcement contributing to bending of coupling beams in loading stage are all discussed.The research of this paper has gained the following achivements:①The program which considered the statically indeterminate strut-tie in the constraint of the wall limb in this paper can reflect the stress performance in the process of the composite reinforcement coupling beams in different axial constraint conditions.②Analysis shows that the degree of the constraint of the coupling beams’ axial deformation has a huge influence of its seismic performance, when both ends clamped, the displacement ductility capacity of coupling beams is less than 3.0, it is smaller than the shear wall structure’s demand of the ductility to the coupling beams in rare earthquake.③In the coupled shear wall structure, the ductility capacity of the coupling beams will reduce along with the increase of the size of the wall limb,and the demand of the ductility will increase, when the hight of the wall limb is more than 4500 mm, the composite reinforcement coupling beams whose L/h≤1.5 can not satisfied the demand of the ductility.④The constraint of the slab increase the shear to compress ratio of the coupling beams,and also increase the yield load and the limited load, but it will decrease the displacement ductility coefficient of the coupling beams.