Nonlinear analysis for failure behavior of reinforced concrete beams and frames

Abstract

In this dissertation, methods for predicting the entire behaviors including the softening of reinforced concrete beams and frames due to flexural failure are developed. For structural analysis considering the strain-softening, it is very important to the accurate evaluation for the material nonlinearity. Then the model for the stress-strain relationship of concrete in uniaxial compression is proposed by the regression analysis of the test data by others. In the strain-softening analysis, the displacement control method is one of the widely used methods. But it is a fatal shortcoming for the loss of the symmetrical and banded nature of the stiffness matrix. Therefore, in order to keep the symmetry and to include the nonproportional loading, the displacement control method is newly modified. To predict the entire load-deformation characteristics, solution techniques are developed. The nonlayered method in beams is proposed by using the model for the moment-curvature relation. For frames, the combined layered and nonlayered method is suggested. To demonstrate the validity of this algorithm, the analytical results are compared with the experimental results by several investigators. The proposed method reduce greatly the computational time and needs the very small space of the computer main memory with comparison to the present layered method. Therefore, this method provides a more efficient and economical method for a complete analysis of reinforced concrete structures. Accordingly, it is possible to application for analysis of some more large scaled structures without using additional auxiliary system. The analytical result leads to spurious sensitivity to the chosen element size in both beams and frames. This problem is overcome by modifying regidities and curvatures for each element based on the concept of concentrated inelastic rotations at plastic hinge considering the applied axial load.