Optimum Distribution of Story Shear Force Coefficient for Energy Based Seismic Design Process

Abstract eng:
Typically, the story shear force acting horizontally on a multi-story structure is proportionally calculated to the height of and weight acting upon each story. The story shear force distributions of most seismic design codes generally reflect the influences of higher vibration modes based on the elastic deformations of structures. However, as the seismic design allows for the plastic behavior of a structure, the story shear force distribution shall be effective after it is yielded due to earthquake excitation. Hence, this study conducted numerical analyses on the story shear force distributions of most seismic design codes to find out the characteristics of how a structure is damaged between stories. By conducting the static and dynamic response analyses based on the calculation formula for the story shear force distribution, which is proposed by the seismic design code of several countries, in this paper we weigh the behaviors of a multi-story structure including plastic deformation, and analyze the characteristics of damage distribution caused by ground motion. Considering the nature of distribution of story shear force coefficient, which appears in the story-specific distribution, a beam with infinite stiffness and the 2D framework were applied to the model shape for response analysis in order to facilitate the story-specific design and the analysis of response characteristics. Analysis results show that the more forces are distributed onto high stories, the lower its concentration is and the more energy is absorbed. In comparison of the distribution of cumulative plastic deformation ratios of analytical models according to a variety of input earthquake motions, the models KBC2009 and IBC2006 with the linear type distribution of story shear force coefficients showed that the damage was tended to extremely concentrated in top portion. The models UBC97, NZS1170, AIJ and H.Akiyama with the distribution of story shear force coefficients in curvilinear form showed that the layer damage was relatively well dispersed compared to the models KBC2009 and IBC2006. In analyzing the layer damage intensity and the energy absorption at limit state, the seismic efficiency of H.Akiyama model with the largest increase in distribution of story shear force coefficients in top portion was excellent. We drew the optimum distribution of story shear force coefficients, implementing the optimum distribution of layer damage in which the damage distribution uniformly appears on all stories for analytical models having a variety of natural periods, and proposed the calculation formula with variables resulted from analyzing the optimum distribution of story shear force according to the changes of natural periods. With the analytical models in the same conditions, the damage distribution by the proposed calculation formula showed the most equitable form in comparison to the layer damage distribution obtained from the distribution of story shear force coefficients based on the seismic design code of several countries. From the results, this study proposes the optimum story shear force distribution and its calculation formula that make the damages uniformly distributed onto whole stories. Consequently, the story damage distribution from the optimum calculation formula was considerably more stable than existing seismic design codes.

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