Study On Shear Model Of Diagonally Cross-Reinforced Coupling Beams With Small Span-Depth Ratio And Its Application In Nonlinear Dynamic Response Analysis

Shear wall system,frame-wall system and frame-tube system are commonly used structural systems in high-rise buildings.Coupling beams not only enhance the lateral strength and lateral stiffness of structures,but are also key components to ensure structural ductility and palstic energy dissipating capacities in such structures.As nonlinear dynamic response analysis has been more and more widely used in seismic design and performance assessment of high-rise buidings,it is particularly important to propose a simple and efficient numerical simulation model for coupling beams.As a structural seismic performance assessment software,PERFORM-3D has been widely used in China’s structural seismic research and engineering practice and it has gained substantial recognition and acceptance in the scientific research and engineering field.Shear and bending performance are separately considered in PERFORM-3D.Generally,shear performance of slender coupling beams is considered as elastic,while in small span-depth ratio coupling beams,shear deformation accounts for a large proportion in total deformation so that it cannot be ignored in modeling and a reasonable shear model should be used.Compared with other small span-depth ratio coupling beams,the diagonally cross-reinforced coupling beams proposed by our team(coupling beam in figure 11.7.10-1 of article 1 of China’s Code for Design of Concrete Structures)have better ductility capacity and most of them can achieve a displacement(or rotation)ductility capacity of more than 4.2,even 4.6 can be achieved under a high shear force ratio equal to 0.30.In addition,the reinforcement scheme will not seriously increase the difficulty of construction.Therefore,this kind of coupling beams is the recommendation in engineering practice.However,there is no research result found out about the shear model for diagonally cross-reinforced coupling beams with small span-depth ratio at present,so it’s necessary to study it.In this paper,after verifying the effectiveness of finite element model for diagonally cross-reinforced coupling beam with small span-depth ratio,A reasonable method was selected to separate shear and bending deformation and diagonally cross-reinforced coupling beams with small span-depth ratio were analyzed at component level with influence of various factors on characteristic parameters of shear and flexural models considered.Based on the influence of different factors on the models’ characteristic parameters,simple and practical shear and flexural models were established and verified to be valid.Finally,the established models in this paper were applied to a structural example to identify the ductility requirements of diagonally cross-reinforced coupling beams with small span-depth ratio in order to verify if the reinforcement scheme was effective.The main conclusions of this paper are as follows:(1)The simulation results of diagonally cross-reinforced coupling beam members with small span-depth ratio in this paper were in good agreement with test results,and the program VECTOR2 was proved to be ideal for simulation of diagonally cross-reinforced coupling beams with small span-depth ratio;(2)The calculation of shear deformation merely based on the X-shaped diagonal deformation was only applicable to members with uniform curvature distribution,so the shear deformation needed to be corrected.In this paper,bending deformation was first calculated by the method proposed by Hiraishi with segmented model,and then shear deformation was obtained by subtract the bending deformation from total deformation;(3)Based on influence of various factors on the characteristic parameters of shear and flexural model for diagonally cross-reinforced coupling beams with small span-depth ratio,the mathematical expressions of the characteristic parameters were determined,and thus the shear and flexural model were established and verified to be valid by the program PERORM-3D.The model forms and the specific expressions of characteristic parameters could be found in Chapter 4;(4)This paper used the program PERORM-3D to analyze the nonlinear dynamic response of an actual engineering structural with fortification intensity of 8 degrees(0.3g)under severe earthquake,which was partially equipped with diagonally cross-reinforced coupling beams with small span-depth ratio.The results showed that the maximum rotation ductility requirement for diagonally cross-reinforced coupling beams with small span-depth ratio was 2.66,which was less than the rotation ductility capacity of 4.2 that most of such small span-depth ratio beams could achieve in our team’s test results with a large ductility margin.This reinforcement scheme was proved to be able to meet the ductility requirements of coupling beams in the structure with a large ductility margin,so such reinforcement scheme was proved to be effective.The main innovations of this paper are as follows:(1)By the finite element analysis of diagonally cross-reinforced coupling beams with small span-depth ratio and separation of shear and bending deformation,the shear model and flexural model suitable for this kind of beams were established in this paper to make up for this research vacancy and solve the key problems of simulating this kind of coupling beams in structural system analysis;(2)The nonlinear dynamic response analysis on a practical engineering structure partially equipped with diagonally cross-reinforced coupling beams with small span-depth ratio was performed to identify the ductility requirements of such coupling beams in the structure and validate if the reinforcement scheme was rational and effective.