Experimental Research And Numerical Modeling On Seismic Behavior Of Frost-damaged RC Shear Walls

It is well known that frost action in cold regions is one of the main reasons for the decline in mechanical properties of concrete.The degradation of concrete mechanical properties caused by freezing-thawing damage is also one of the main reasons deteriorating the seismic behavior of reinforced concrete(RC)members.Since early design stands for concrete members did not take frost action into consideration,some inservice RC members are venerable to frost attack,resulting in the degradation of concrete members' mechanical properties and seismic behavior.In Northeast China,the winter has a long duration with low temperatures and large temperature variations between day and night,reinforced concrete(RC)members are repeatedly subjected to a freeze-thaw cycle every year,and the deterioration of RC members caused by frost action is becoming increasingly significant.Damage of RC members caused by frost action has attracted significant attention for several decades in Japan,Canada,and North America.Meanwhile,these RC members may also locate in earthquake fortification regions.Based on this,this paper selects the RC shear wall commonly used in high-rise buildings as the research object,and carries out the seismic performance test and numerical simulation research.The main research contents and conclusions involved are as follows:(1)The artificial climate rapid frozen thawed process was used to create the cold environment.It is carried out the consecutive FTC tests and pseudo-static tests on eight RC shear walls to systematically research on the impact of concrete strength,the number of FTCs,and axial load ratio on the seismic behavior of frozen-thawed damage squat walls.The experimental results indicated that as the number of FTCs increased,the flexural-shear failure of the RC shear walls shifts from a flexure-dominated mode to a shear-dominated one.Meanwhile,the load carrying capacity,deformation capacity,and energy dissipation capacity gradually decreased,whereas the declining rate of deformation capacity and energy dissipation capacity,the average shear distortion and the ratio of shear deformation to the total specimen deformation under different loading states gradually increase.As the concrete strength grade improve,the load carrying capacity,energy dissipation capacity,peak shear distortion and its contribution to the total specimen deformation gradually increase.Furthermore,the rate of improvement of load carrying capacity and energy dissipating capacity is more obvious,and the ductility coefficient first increases and then decreases.As the axial load ratio increases,the load carrying capacity of the RC shear walls progressively strengthened,whereas the deformation capacity,energy dissipation capacity,yielding and peak shear distortion gradually deteriorate.Moreover,the increasing rate of the load carrying capacity obviously reduces,whereas the decreasing rate of deformation capacity and energy dissipation capacity obviously increase.The ratio of shear deformation to the total specimen deformation gradually decreases in the yielding state and gradually increases in the peak state.(2)Theoretical analysis and experimental regression are combined to analyze and deal with the data of frost-damaged RC shear wall quasi-static test.Considering the influence of freeze-thaw damage parameter and axial load ratio on the ultimate work ratio index and the load carrying capacity and deformation capacity deformation of frostdamaged RC shear wall under different loading conditions,the calculation model of ultimate work ratio index and characteristic point parameters of skeleton curve of RC shear wall members with freeze-thaw damage was established.At the same time,considering the strength attenuation,stiffness degradation and pinching effect,the stiffness change of the unloading section of the hysteretic loop was represented by a twofold line model.The hysteretic model of RC shear wall members damaged by freeze-thaw was established and compared with the test wall.The accuracy of the model was verified from the hysteretic curve and cumulative hysteretic energy dissipation.The results are in good agreement with each other,which shows that the hysteretic model can reflect the mechanical and seismic performance of frost-damaged RC shear wall.(3)The quasi-static test data of eight frost-damaged RC shear walls with were theoretical analysis and experimental regression.The shear recovery model of RC shear walls with freeze-thaw cycle and axial compression ratio was obtained by multi parameter nonlinear surface fitting.A shear hysteresis model of squat RC shear wall considering the effects of frozen-thawed damage parameter and axial load ratio is obtained.At the same time,combined with the uneven freeze-thaw effects,a numerical simulation method of RC shear wall with non-uniform freeze-thaw damage distribution combined with shear effect and bond slip effect was proposed.By comparing the simulation results with the existing test results,it is found that the hysteresis curves obtained by the simulation are in good agreement with the test results.Which indicates that the numerical simulation method proposed in this paper can accurately reflect the mechanical performance,and seismic performance of frost-damaged RC shear wall damaged,and can provide a theoretical basis for the seismic performance evaluation of in-service shear wall in severe cold area.