Seismic Behavior Of High Strength Reinforced Concrete Shear Wall Partially Strengthened With UHPC

Cold rolled high-strength steel bar CRB600 H is a new type of ribbed bar with small diameter developed in recent years.It is superior to ordinary cold-rolled ribbed bar with good machinability.The strength of CRB600 H rebar exceeds hot rolled rebar HRB400 which is commonly used in practice.Besides,the bonding performances with concrete are higher and the cost is lower.The use of CRB600 H as the reinforcement in structural members can reduce the amount of rebar,the cost and construction time.In addition,the total energy consumption is lower than that of ordinary low-alloy hot-rolled reinforcement as the cold rolling process can effectively reduce the use of alloy.Thus the social and economic benefits are significant,which is in line with the national high-quality development strategy.Cold-rolled rebars are mainly used as distribution reinforcement in shear wall in current Chinese codes.In order to fully utilize the high strength of CRB600 H and study its feasibility as primary reinforcement,it is necessary to further improve the performance of concrete.Ultra high performance concrete(UHPC)has excellent mechanical properties,such as high strength,high crack resistance.UHPC can be used with high strength rebar as partial replacement of the concrete in shear wall under high stresses,which may improve the seismic performance of the structure and reduce the damage of structure.In this study,the seismic performances of reinforced concrete(RC)and UHPC shear wall with CRB600 H reinforcement in boundary elements are investigated by means of cyclic loading test,numerical simulation and theoretical analysis.The main contents and results are as follows:(1)Six RC shear walls with CRB600 H reinforcement in boundary elements were designed for cyclic loading test.The mechanical characteristics and failure mechanism of shear walls with different longitudinal reinforcement in boundary column,reinforcement ratio were studied from the perspective of crack distribution and other factors.All the shear walls showed flexuralshear failure.The distribution range of cracks in the shear wall with CRB600 H reinforcement in the boundary column was wider than that with HRB400.The former has smaller residual deformation and pronounced secondary stiffness after yielding.The bearing capacity was higher but the energy consumption decreased.(2)Two shear walls with CRB600 H reinforcement and UHPC in boundary elements were fabricated for cyclic loading test,and the seismic performance was compared with RC shear wall under equal reinforcement ratio.It was found that the initial crack of the specimen with UHPC was delayed and the development of the crack along was significantly restrained both along horizontal and vertical directions.The residual deformation was smaller and the stiffness degradation was further controlled.The bearing capacity was further improved and the failure was governed by the fracture of CRB600 H rebar.(3)SFI-MVLEM was selected to model the shear wall specimen in Open SEES.The shape,residual deformation and capacity of the simulated hysteretic curve agreed well with the experimental results.In addition,the parameters of axial compression ratio and strength of steel were analyzed.It was found that the increase of axial compression ratio was beneficial to the improvement of the capacity when it did not exceed 0.4;while the growth of bearing capacity of RC shear wall slowed down obviously as the axial compression ratio was greater than 0.4.When the strength of longitudinal reinforcement in boundary column was increased to 970 MPa,UHPC didn’t fail in compression.(4)Based on the plane section assumption,different types of concrete in the compression area were considered respectively.The position of the neutral axis in the bottom section was determined.Calculation method for the flexural capacity of different concrete shear walls with cold rolled high strength reinforcement was proposed.The results obtained by the proposed approach were in good agreement with the experiment with certain level of conservativeness.The calculation method of shear capacity of reinforced with cold rolled high strength reinforcement was proposed based on the truss arch model by considering the concealed column and web in the shear wall.The differences between the prediction and test results were less than 10%.