Use of 3-Dimensional Nonlinear Response to Multi-Directional Ground Motions in Earthquake Resistant Design of Reinforced Concrete Frames

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An analytical model of a reinforced concrete column, which has two sets of multiple rotational inelastic springs at the both ends of an elastic flexural rod, is newly developed to analyze the interaction effect of bi-axial bending. The results of 3-dimensional response analysis of one-story frame models subjected to bi-directional strong ground motions show that the damage to columns and the story response of the frames can be increased by the interaction effect of the bi-axial bending of columns.To investigate the effect of time-varying axial load in columns on the earthquake response of a building, a simplified SDOF model, which is equivalent to longitudinal frames of a eight-story reinforced concrete building and has fiber-slice models for columns in the first story, is analysed considering the time-varying axial load in columns induced by the overturning moment of the transverse frame. It is illustrated that the high level of variation of axial load may cause the increase in the damage and the reduction of the lateral strength of the columns.Three dimensional earthquake response of an eleven-story reinforced concrete building with a setback is analysed by the method considering the inelastic characteristics of the constituent member. The relationship of the distribution of the lateral strength of frames and the distribution of the damage to frames is investigate. It is shown that the strength distribution of frames based on the distribution of the shear forces of the frames by the static or dynamic linear analysis may lead to the uniform damage distribution.