Studies On Seismic Performance Enhancements,shrinkage And Creep Effects Of Precast Superimposed Reinforced Concrete Shear Walls

The precast superimposed reinforced concrete shear wall(SRCSW)structure is in the promotion stage of application in China.With the merits in terms of fitting for industrial production,standardized construction,the SRCSW system meets the great need of the upgrading of the precast(PC)constructi on industry in China.To satisfy the requirement of sufficient seismic resistan ce in most seismic-prone area national wide and the great demand for high-rise buildings during the development of urbanization in the Chinese mainland,the enhancement of seism ic performance of SRCSW is essential.Moreover,for the reason that the SRCSW is cast by different batches of concrete,the accurate calculation for the shrinkage and creep effect is necessary for the normal usage of such a wall system.Therefore,the improvements of seismic performance and the investigation on the shrinkage and creep effects of SRCSW are focused on in this paper.By means of the experimental method,numerical simulation and theoretical analysis,t he seismic behavior of SRCSW under earthquake load,the shrinkage and creep effect under environmental changes and long-term axial load were evaluated.The main work of this study is presented as follows:(1)In order to enhance the seismic performance of SRCSW,a n innovative SRCSW(ISRCSW),of which the cavity was embedded by steel plates formed as X-shaped steel bracing,was proposed.By conducting a quasi-static test,the seismic performance of ISRCSW specimens,traditional SRCSW specimen and cast-in-place(CIP)specimen was compared,and the superiority in seismic resistance of ISRCSW was verified.(2)By means of modifying the connection joint,the spiral hoop and bolted steel plate connections are introduced into the ISRCSW system to improve the seismic behavior.The seismic performance of such ISRCSW specimens was compared with the CIP specimens by cyclic loading test,which indicates the acceptable construction feasibility and applicability of the two proposed connection joints.(3)Based on the elastic mechanic theory and the section feature of the shear wall,the calculation formula of elastic stiffness,cracking load,shear capacity for the ISRCSW were deduced.In accordance with the assumption of plane section,the flexural capacity was derived.By analyzing the exisiting experimental test data,a three-point skeleton curve and hysteretic model for the load to displacement relationship of ISRCSW were concluded.(4)Considering the nonlinear slippery relationship along the horizontal and vertical direction,solid element based models p erformed by ABAQUS and simplified layered shell element based models performed by Open Sees were established,respectively.By contrast with the test results,the two types of finite element analysis(FEA)models were verified through numerical simulation by conducting monotonic load and cyclic load test s.Based on the established FEA models,the parameters in terms of the axial load rati o,the characteristics of X-shaped steel bracing,the arrangement of lap-splicing rebar in the horizontal connection joint as well as the features of the hidden columns,which may affect the seismic behavior of ISRCSW,were parametrically investigated.(5)A small size SRCSW specimen was designed and manufactured,of which the wire vibration strain gauges were fixed in the PC layer and CIP layer.In line with the process from casting and curing to the usage,the shrinkage effect at the early curing stage and creep effect at the loading stage of the shear wall specimen were recorded.(6)According to the self-drying resulted from the hydration of concrete and the humidity diffusion caused by the humidity difference,the internal humidity field model of the SRCSW specimen was established,and the humidity distribution inside the wall specimen was calculated by using the finite difference method.And then the strain field of the SRCSW specimen was derived by applying the GL2000 theory on the prediction of the shrinkage effect.Based on the above analytical model,the factors such as the width of the shear wall,the environmental humidity and the concrete strength which may affect the distribution of humidity and strain,were discussed.Furthermore,the cracking risk due to the shrinkage stress was evaluated.(7)According to the deformation coordination of concrete and reinforcements inside the shear wall specimen under the long-term axial load,the strain model was performed by using the age-adjusted effective modulus method(AEMM)and the stress of the cross-section were deduced.Based on the GL2000 theory,the calculation model for calculating creep effects of the SRCSW sp ecimen was established.Lastly,the influences of concrete strength,vertical load,curing age,the loading age and environmental humidity on the creep effect of SRCSW were compared.