| Reinforced concrete(RC)shear walls are used as the primary lateral-load resisting components in high-rise building structures.Under strong ground motions,RC walls in high-rise buildings may be subjected to axial tensile load,and thus experience a critical condition of combined axial tension-flexure-shear loading.This thesis investigates the combined axial tension-flexure-shear behavior of moderate-aspect-ratio RC walls using large-scale experimental tests,theoretical analysis and finite element simulation.The main work and achievements are as follows.(1)Quasi-static tests were conducted on four large-scale RC wall specimens with a moderate aspect ratio of 1.5.The specimens were subjected to axial tension force and lateral cyclic loading.The influence of axial tension on seismic behavior of RC walls was investigated.When the axial tensile force changed,various failure modes,including shear failure,flexural-shear failure and flexural failure were observed for the specimens.The axial tensile force was found to significantly influence the lateral strength capacity and stiffness of RC wall specimens.When the normalized tensile stress of vertical reinforcement increased from 0.20 to 0.80,the maximum lateral strength decreased by 55% and the lateral effective stiffness decreased by 32%.The vertical strain distributions along the wall bottom section basically satisfied the plane section assumption before the specimens reached the maximum lateral strength.Significant axial elongation was observed for the wall specimens subjected to combined axial tension force and lateral cyclic loading.(2)Shear-flexure interaction of the moderate-aspect-ratio RC wall specimens was investigated based on test data and theoretical analysis.Prior to the yielding,flexural deformations contributed over 60% of the lateral displacement for all specimens.After yielding,significate shear deformations were developed for all the specimens because the inelastic flexural deformations of the walls led to remarkable inelastic shear deformations developed in pelastic hinge region.The shear deformation contributed 49%～57% of the lateral displacement at the maximum lateral strength of specimens.After flexural yielding,the axial elongation of walls resulted in degradation of their shear strength capacity,and consequently led to the mechanism transition from flexural mode to shear mode for specimen MSW2.The flexure-shear failure mechniasm was quantitatively analyzed,where the flexural strength was estimated based on the plane section assumption and the shear strength degradation was estimated using the rotating-angle softened truss model and measured data of axial elongation.(3)Finite element(FE)models were established using the cyclic softened membrane model in Open Sees program.The analytical results were in good agreement with the test data.Design formulae of strength of RC walls were calibrated with test data and FE analysis.Both U.S.code ACI 318-14 and Chinese standard JGJ 3-2010 formuae can provide a reasonable estimates of tension-flexure strength of RC walls.The calculated values were close to the test yield strength.For tension-shear strength,The JGJ 3-2010 formulae,the ACI 318-14 formulae,the equation proposed by Xiao et al and the equation proposed by Cheng were compared.The mean value of experimental/FE analytical-tocalculated ratios are 1.54,1.60,1.56 and 1.40 for these four formulae,respectively.The standard deviations of experimental-to-calculated ratios are 0.44,0.57,0.47 and 0.28,respectively.The equation proposed by Cheng reasonly reflects the influence of boundary longitudinal reinforcement and axial tensile force,and it has a larger reliability index value than other equations.Therefore,this equation is recommended to use for calculation of tension-shear strength of RC walls. |
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