Effect of vertical irregularity on displacement concentration in building seismic design based on linear analysis

Recently, earthquakes with a magnitude of 5.0 or more have occurred in Pohang and Gyeongju in Korea, and the demands for seismic performance evaluation of buildings has been increasing. In particular, in the case of Pohang earthquake induced a significant damage to the middle and low rise piloti buildings. The purpose of this paper is to investigate the effects of displacement concentration on the buildings with the vertical irregularity subjected to horizontal shear forces. Displacement Concentration Factor (DCF) was defined as the displacement ratio of the first story to the top story to quantitatively analyze the degree of displacement concentration between equivalent static analysis and response spectrum analysis for the buildings with vertical irregularity. Displacement Concentration Amplification Factor (DCAF) was defined as the DCF ratio of the response spectrum method to the equivalent static analysis to compare displacement concentration on soft story. In this paper, DCAF according to the stiffness ratio of soft story and the number of story was analyzed through 2D model. Also DCAF value of 2D model was verified by 3D prototype model of 4-story piloti structure. The DCAF value tended to increase as the stiffness ratio decreased and the number of story increased. It was confirmed that the response spectrum method should be applied instead equivalent static analysis when the DCAF value is 1.35 or more according to the criteria of KBC 2016.