Study On Shear Capacity And Deformation For Reinforced Concrete Structure Based On Modified Compression Field Theory

For reinforced concrete members, shear failure mechanism is a complex issue. It is not yet fully understood. To this day, many shear analysis methods for reinforced concrete have been developed, including truss theory, limit equilibrium theory, statistical method, fracture mechanics method and nonlinear finite element method. Truss theory includes classical 45-degree truss model, improved truss model, compression field theory, modified compression field theory, disturbed stress field theory, softened truss theory, truss-arch theory and so on. In these theories, modified compression field theory, MCFT, developed in 1980s based on the research of Michael P Collins and his co-workers at the University of Toronro has opened up a new way of resolving the shear of reinforced concrete structures, and have been widely recognized by the international community so far. This theory has been used in the Canadian codes and the American codes.The past research has been primarily focused on estimation of the maximum lateral load capacity of reinforced concrete columns or shear wall rather than the load-deformation relation, which includes flexure, bond-slip and shear deformation components. Nevertheless, the effect of transverse loading, e.g., as in an earthquake, on reinforced concrete column or shear wall behavior has been an attractive topic of research for the last few decades. In recent decades, a few of theoretical models presented continuous monotonic lateral load-shear displacement response for RC panels or beam-columns on basis of mechanical fundamentals were developed, e.g. MCFT. Many researchers used analysis results of this theory to develop simplified lateral load-shear deformation response envelops of reinforced concrete compressive members.In this paper, a further research was made based on the modified compression field theory. The detailed works listed as follows:1. A further research on reinforced concrete beams without stirrups was made based on the MCFT. An expression of the average shear stress across the crack was derived and a simplified equation of shear strength considering the size effect in shear was developed. The obtained equations were verified with extensive sets of experimental data from different source (512data in total). It was found that the variation coefficients of ratio of shear strength calculated using the derived average shear stress across the crack based on modified compression field theory and simplified expressions to test data is small. Thus, it is suitable for shear analysis and design of reinforced concrete beams without stirrups.2. The shear capacity of RC members calculated by MCFT was underestimated due to ignortion of the shear carried by concrete in compression zone. According to shear failure mechanism of reinforced concrete members, a further research on reinforced concrete beams with stirrups was made based on the MCFT. A general method and its simplified method of the shear capacity considering the shear contribution of concrete in compression, shear stress transmitted across crack interface, and stirrups based on shear failure mechanism of reinforced concrete member were developed and verified with extensive sets of experimental data from different source (275 data in total). It was found that consistency between shear strength calculated using the derived expressions and test data were well. So it is suitable for shear analysis of reinforced concrete beams.3. To model lateral load-deformation relationship for reinforced concrete columns subjected to combined action of axial load and lateral load, a new method is developed using MCFT to model shear behavior and conventional section analysis to model flexure behavior, and considering the total lateral deformation of a column at its ends is comprised of deformations due to flexure and shear. The lateral load-deformation courses of reinforced concrete column failing in flexure, flexure-shear and shear can be presented in this method. Finally, the proposed model is compared with 15 rectangular columns from various low-cycle reverse loading tests. In general, the model predicted the lateral load-deformation response envelop reasonably well, so it can be used in lateral load-deformation analysis for reinforced concrete columns subjected to combined action of axial load and lateral load.4. The finite element procedure herein is made to reflect the nonlinear behavior of reinforced concrete shear wall by adopting the stress-strain formulations of the MCFT. In this method, aggregate interlock force along crack is calculated by proposed average shear stress formula. Such analysis is based on a secant stiffness formulation and utilizes only the lowest order finite elements (rectangular elements). The obtained lateral load-deformation response by this procedure has yielded excellent agreement with experimental results. This method can be used to predict the nonlinear behavior of shear wall, deep beams and other components up to the maximum shear strength.