Experimental Study On Tension-Shear Performance Of Reinforced Concrete Shear Wall

In the past,due to the small height-to-width ratio of structure,the shear wall was rarely in tension state.Recently,with the increase of building height,the height-to-width ratio of structure has increased gradually.The axial tensile force may be large when the high-rise building was to resist overturning moment.The shear wall may be in tensile loading after overcoming the compression force which was generated by vertical loads such as its own weight.At this moment,the shear wall was in complicated state under the combined actions of tensile force,shear force and bending moment.This is damaged to the safety of structure.The formula for calculating the shear capacity of eccentric-tension shear wall in code GB50010-2010 “Code for Design of Concrete Structures” and code JGJ3-2010 “Technical Specification for Concrete Structures of Tall Building” were derived by the formula for calculating the shear capacity of eccentric-compression shear wall,which haven't been certificated by tests.Therefore,it is necessary to study the tension-shear performance of reinforced concrete shear wall.In this paper,the tension-shear performance of reinforced concrete shear wall was studied by specimens' tests and finite element analysis.The main contents include:(1)In two groups with sectional longitudinal reinforcement ratios of 1.7% and 2.5% respectively,11 specimens of shear wall with shear-span ratio of 1.5 were tested for their tension-shear performances by low-cyclic repeated loading tests with fixed axial force.The test results show that under the combined actions of tensile force and shear force,and depending on the relative magnitude of the two forces,shear walls may be in the tension state of large eccentricity or in the tension state of small eccentricity,which leads to the shear-compression failure mode or the slip failure mode,respectively.The influences of tensile force and sectional longitudinal reinforcement ratio on the seismic performance of shear wall were analyzed.The test results show that the shear capacity,horizontal lateral stiffness and cumulative hysteretic energy of shear wall may be increased with the increase of sectional longitudinal reinforcement ratio or may be increased with the decrease of tensile force.But the equivalent viscous damping coefficient of shear wall may be decreased with the increase of sectional longitudinal reinforcement ratio or may be increased with the increase of the tensile force.In addition,the tensile force and sectional longitudinal reinforcement ratio have a positive effect on the deformation capacity of shear wall.Compared with the compression-shear failure mode,the ductility and ultimate deformation capacity of shear wall were increased in tensile loading.The deformation capacity of shear wall may be increased with the increase of sectional longitudinal reinforcement ratio.(2)Low-cyclic repeated shear tests of tension-compression variable axial force were carried out on two specimens of shear wall with sectional longitudinal reinforcement ratio of 3% and shear-span ratio of 1.5.The test results show that when shear wall repeatedly switched between tension-shear state and compression-shear state,yielding occurred in the tension-shear stage and fragile failure occurred in the compression-shear stage.Compared with the tension-shear state,the bearing capacity of shear wall in the compression-shear state was larger and reached peak value earlier,and the deformation was smaller.The shear capacity and the deformation capacity of shear wall decreased with the increase of target axial force.Axial force increase the difference of shear capacity of shear wall in the tension state and in the compression state.Compared with shear test results of fixed axial force,the tension-shear capacity of shear wall under the shearing of tension-compression variable axial force was reduced,and the compression-shear capacity was not changed significantly.(3)The formulas of calculating the tension-shear capacity of eccentric-tension shear wall under two failure modes were proposed.The term of boundary longitudinal reinforcement was added to the shear capacity formula of shear-compression mode.The influence coefficients of tension force and boundary longitudinal reinforcement in the shear capacity formula were-0.2 and 0.04 respectively in the shear-compression failure mode;and the influence coefficients of tension force and section longitudinal reinforcement in the shear capacity formula were-0.6 and 0.6 respectively in the slip failure mode.The formula of critical point for the shear-compression mode and the slip mode was derived,and the formula shows that for higher axial force,the specimens with lower longitudinal reinforcement ratio tend to fail in the slip mode.(4)The two-stage formulas for calculating the axial tension-stiffness of reinforced concrete shear wall before and after cracking were proposed,and the tension constitutive model of concrete which was modified at the stress descending portion was proposed.According to the physical mechanism of axial tension-stiffness of shear wall,two-stage formulas of axial tension-stiffness of shear wall were proposed: before or after shear wall cracking,the axial tension-stiffness of shear wall would be calculated by the tensile modulus which can be obtained from the tension constitutive model of concrete,or calculated by introducing the non-uniformly distributed strain coefficient of reinforcements.The theoretical curve of axial tension-stiffness of shear wall fit very well with the test results,and can reflect the characteristics of shear wall in tension state.Based on the test results,the tension constitutive model of concrete which was modified at the stress descending portion can better reflect the tension characteristics of shear wall,and can be applied to the structural nonlinear analysis.(5)The tension constitutive model of concrete which was modified at the stress descending portion was applied to the nonlinear analysis of a frame-core wall structure.The seismic performance and failure mechanism of frame-core wall structure which influenced by tensile walls were studied through static and dynamic nonlinear analysis methods.The results show that in order to resist the overturning bending moment which was caused by horizontal force,the axial force of the “flange wall” which was perpendicular to the direction of the external force changed significantly and the shear wall will be in tensile loading state.Because of the insufficient flexural capacity of “flange wall”,the structure cannot resist external forces any more and was destroyed.Compared with the constitutive model of concrete in code,the constitutive model of concrete modified at stress descending portion can more reasonably reflect the capacity and deformation performance of structure,and the changes in internal forces and stiffness of core wall.