Research On Design Method Of Frame-shear Wall Structure Considering P-? Effect

Frame-shear wall is a structural form widely used in high-rise buildings.How to consider the influence of its second-order effect(especially P-? effect)during design is an important issue in structural design.In recent years,scholars from all over the world have made some progress in studying the influence laws and design methods of second-order effects in structures.However,due to the complexity of second-order effects,various methods in engineering design circles are still limited and need to be further verified,especially the simplified calculation method for practical engineering design.Therefore,on the basis of understanding the effects of material nonlinearity,geometric nonlinearity,and second-order effects on the internal forces and deformation laws of structures,a reasonable and correct calculation method is proposed,which has important guiding significance for engineering applications and engineering design.This paper is based on the design of frame-shear wall structure mentioned in Technical Specification for Concrete Structures of Tall Building JGJ3-2010.Based on the analysis of characteristics of force and deformation of frame-shear wall structure under different circumstances of the proportion of overturning moments in frame part taking into account the second-order effects,this paper adopts comparative analysis and founds the problems existing in calculating the P-? effect of frame-shear wall structure in “Overall Increase Coefficient Method” of the current specification.Then the suggestions for improvement methods are given.The work done during the research process and the main results achieved are:(1)Through screening of components of lateral deformation in frame-shear wall structures,it demonstrates that from the quantitative point of view,the frame-shear wall structure increases with the proportion of overturning moment in the frame part,and the structural deformation gradually changes from bending deformation to shear deformation.(2)Based on the comparison of the finite element method(elastic second-order analysis method)and iterative method to calculate the structural P-? effect accuracy,the iterative method is used as the analytical framework to analyze the second-order effect of the frame-shear wall structure.(3)Through the comparative analysis of the designed series of examples,it is found that with the increase of the frame overturning moment in the frame-shear wall structure,the shear deformation component of the structure under the horizontal load increases,the overall deformation characteristics of the structure have changed,and the “Overall Increase Coefficient Method” that considers the P-? effect mentioned in current specification has not been fully applicable.(4)After summarizing,proposed methods for calculating the P-? effect of frame-shear wall structure are: For the structural deformation check under normal use limit state,as the nonlinear characteristics of the material are not obvious,the stiffness of the component is not reduced when calculating the displacement increase coefficient.For the structural analysis under the limit state of the bearing capacity,we should consider the reduction of the member stiffness according to the specification because the influence of non-linear material development on the internal force change can not be ignored.For the frame-shear wall structure whose frame overturning moment ratio is less than or equal to 50%,the calculation of displacement increase coefficient and internal force increase coefficient still use the “Overall Increase Coefficient Method” in Technical Specification for Concrete Structures of Tall Building JGJ3-2010.For frame-shear wall structures whose frame overturning moment ratio is greater than 50% and less than 80%,it is recommended that the displacement should be calculated by using the elastic second-order analysis method where the stiffness of the member is not reduced,and its second-order internal force should be calculated by using the elastic second-order analysis method for the stiffness reduction of members.For the frame-shear wall structure whose frame overturning moment ratio accounts for more than or equal to 80%,it is recommended to use the elastic second-order analysis method to consider its P-? effect.If a simplified calculation method is used,the overall displacement increase coefficient of the structure and the internal force increase factor of the frame part can be calculated according to the “Layer Increase Coefficient Method” in Code for Design of Concrete Structures GB50010-2010.The “Overall Increase Coefficient Method” can still be used for the internal force increase coefficient of the wall section.(5)Based on OpenSees,the nonlinear analysis of frame-shear wall structure with frame overturning moment accounting for 80% demonstrates the feasibility of the proposed method.