Study On Restoring Force Models And Structural Composition Of Concrete Core Walls With Concealed Steel Plate Bracings

Core wall is widely used in super high-rise buildings because of its high lateral stiffness and spatial effect.At present,the researches on core wall mainly focus on the influence analysis of design parameters,the optimization of seismic behaviour and the nonlinear finite element calculation model,etc.There are still insufficient researches on the restoring force models and the comparison of different structural composition.Therefore,based on the preliminary test results of the research group,this thesis takes the concrete core wall with concealed steel plate bracings（SPBCW）as the main research object,and the restoring force models and the influence of different structural composition on the seismic behaviour of core wall are studied by the finite element software Open Sees.The main research contents are as follows:（1）Based on the existing experimental studies,the finite element analysis model of the SPBCW is established by selecting appropriate element types and reasonable material constitutive relations.The simulation curve is in good agreement with the test curve,which shows that the finite element simulation can fully reflect the seismic behaviour of the core wall specimens under low-cycle reciprocating loads,and verifies the validity of the finite element model.（2）Using the finite element model,the parameter analysis are carried out on the ordinary SPBCW and the SPBCW with profile steel in boundary elements,and the main factors affecting its seismic behaviour are determined.On this basis,the design of the orthogonal experimental model and the nonlinear finite element calculation of each experimental model are completed.Based on the above calculation results,a tri-linear skeleton curve model with yield point,peak point and ultimate point as feature points is proposed.Through analysis and regression,the calculation method of each feature point on the skeleton curve and the hysteresis rule of the restoring force curve are given.The comparison with the existing test results shows that the proposed restoring force models consider various influencing factors,and the calculation results are close to the engineering reality and easy to apply,which provides a theoretical basis for the elasto-plastic analysis of the SPBCW.（3）Through nonlinear finite element simulation,the influence of the configurations of boundary elements on the seismic behaviour of core wall is discussed.The results show that when the steel content is the same,the circular steel tube in the boundary elements has a stronger constraint effect on the concrete than the profile steel.It has a certain improvement effect on the seismic behaviour of core wall,but the improvement is very limited and affected by the size effect.And when the steel content is constant,the corner boundary elements（corner column）of the core wall are equipped with different composite columns.Among them,the square steel tube filled with steel-reinforced concrete column has the most obvious effect on improving the seismic behaviour of the core wall,followed by the square steel tube concrete column,and the improvement effect of the steel reinforced concrete（SRC）column is the least.Among the SRC columns,the circular steel tube has the best effect,followed by square steel tube and cross steel tube.（4）Through nonlinear finite element simulation,the influence of the structural composition of core wall on its seismic behaviour is also discussed.The results show that,when the steel content is the same,compared with the ordinary concrete core wall,the bearing capacity of the core wall with concrete-filled steel tube（CFST）column,profile steel and bracings or CFST and bracings is increased more significantly than that of the core wall with profile steel,steel plate bracings（SPB）or steel truss.The ultimate displacement of the core wall with SPB,CFST column,profile steel and bracings,CFST and bracings is increased more obviously than that of the core wall with profile steel or steel truss.And as the aspect ratio increases or the axial compression ratio decreases,the bearing capacity and deformation capacity of each specimen are improved more than that of the ordinary core wall,the mechanical performance is fully exerted,and the advantages are more prominent.In addition,compared with the ordinary core wall and SRC core wall,the seismic behaviour of the steel plate reinforced concrete core wall have been significantly improved,and when the steel content is constant,the steel plate is mainly configured the bottom of the core wall where is subject to larger force,the improvement of the seismic behaviour is more prominent.The floor lateral displacement curves of each specimen are in a shear-bending type,and the maximum inter-storey displacement angles at yield and failure are all bigger than the limit of code for seismic design,indicating that different structural composition can make the core wall have better seismic behaviour and higher safety reserve.