Disscussions On Modification For The Provisions Of Second-order Effects In Code For Design Of Concrete Structures And Verification For Stiffness Reduction Parameter Of Shear Wall

The guidance of recognition to second-order effect and its design method in reinforced concrete structures becomes more important in structural design. Although research on second-order effect rules and its design method has been made progress recently, there remains a series of important problems needed to clarify, in order to improve the design methods which are now ambiguous in characteristics of RC structure and rely heavily on empirical experience. The research in this paper was driven by the revision of China Standard"Code for Design of Concrete Structure". From the analytical and testing results, this paper made some academic progress as follows:①This paper makes a summary of relative provisions about second order effect in 2002 code, and gets new recognitions, simultaneously comments on the second order effect rules and the design method. Then it perceives and analyzes the overall pattern, specific method and its background in 50010-2010 code, compared with the 2002 national code, it certainly indicates that the modification on provisions of second order effect in 2010 version gets qualitative enhancement. This part in paper is to provide necessary explanations and discusses for the modification of national code.②A series of computer simulations are done in this paper focus on the boundary conditions of P -δeffect provisions in 2010 national codes and analyzing with different influence coefficients such as: concrete strength, unilateral reinforcement ratio, axial compression ratio, reinforcement grade and so on. The analyze results preliminary prove the boundary conditions in the code are suitable. Simultaneously, this paper preliminary discusses the C_mη_ns method in the code, and tentatively analyzes the situation when C_m value or P -δeffect is the dominate factor, which indicates considering second-order effect method in the code is basically proper.③In order to consider the stiffness reduction coefficient at the yield level for inelastic shear wall, this paper chooses the finite element program software ABAQUS to do damage plastic simulation for shear walls with rectangular cross-section, and compares the results of tests with simulation. The comparison shows ABAQUS is suitable to do damage plastic simulation for rectangular cross-section shear walls till the post-yield stage.④Since the stiffness reduction coefficient of shear wall relies heavily on empirical experience in both 2002 and 2010 codes, this paper does simulations of 28 rectangular cross-section shear walls collected from experiments at home and abroad, and gets a stiffness reduction coefficient at the yield stage. After that, this paper simulates shear walls with different concrete strength, moment reinforcement ratio in constraint edge component, compression ratio and aspect ratio to get how these factors influence the stiffness reduction coefficient. It concludes that the concrete strength hardly affects the coefficient. However, the aspect ratio has a big effect on the coefficient. Finally, the paper gathers statistics of tests measured coefficient values respectively on crack level and yield level and coefficient values from 28 ABAQUS simulations and 27 series of examples. On this basis, a proposition of stiffness reduction coefficients respectively on crack level and yield level is given for different aspect ratio shear walls.⑤For the necessary of following works, this paper also does some finite element damage plastic simulations for both'I'and'T'cross section shear walls. The analysis gets load-displacement curves and the normal stress cloud maps of the tension flange, the web and the compression flange, and the results suggest it is proper to simulate'I'and'T'cross section shear walls by ABAQUS. This part is tentative work for simulation of'I'and'T'cross section shear walls.