Evaluation of Safety against Collapse under Strong Earthquake Motion

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Purpose :It has been pointed out from tests, analyses and earthquake damages that column shear forces in beam-yielding reinforced concrete frames could be higher than calculated from an analysis neglecting inelastic axial elongation of beams. The objectives of this study are 1) to develop and verify analytical models, 2) to analyze frames numerically and theoretically, and 3) to establish a simple and rational design formula, for the magnification of the column shear due to the beam axial deformation.Outcome :A computer program for nonlinear analyses of reinforced concrete frames was developed, in which the beam axial deformations due to nonlinear cyclic loading could be simulated as observed in frame tests. The beam model also was verified in detail through the beam tests specially conducted with axial constraint force applied in proportion to the observed elongation. Static and dynamic nonlinear analyses of reinforced concrete frame structures with different parameters, such as beam … More depth, column stiffness, number of spans and stories, were carried out with and without considering the beam axial deformations. The effects of the beam elongation on the column shear were evaluated both analytically and theoretically. A simple and rational design formula for the magnification was derived from the theoretical evaluation based on the mechanical properties of the frames, which was verified through the analytical results.Conclusions :The major findings are : 1) A method for nonlinear and dynamic frame using beam model with inelastic axial deformation was developed, which was verified through the frame tests and the beam tests ; 2) The effects of the beam axial deformations on the column shear of reinforced concrete buildings were investigated through the nonlinear static arid dynamic analyses, from which the column shear forces, especially in the exterior column on compression side, could be much higher than expected from the conventional analysis ; 3) A general and rational design method for the magnification is proposed based on the parameters of the designed frame. Less