SHAKE-TABLE TEST OF A 4-STORY FRAME-WALL RC STRUCTURE TO INVESTIGATE THE COLLAPSE MECHANISM AND SAFETY LIMIT

After an earthquake, it is important to judge the safety of buildings and make an efficient recovery plan. For that, it is necessary to know quantitatively the damage level and safety limit of buildings. An evaluation method of residual seismic capacity is described in the Japanese Standard for Post-earthquake Damage Level Classification of Buildings; however, the method does not consider the difference of deformation capacity of members such as walls and frames (columns and beams). Even though evaluation methods were proposed in previous research for the damage level and safety limit of RC buildings, the focus of the method has been mainly for moment-resting frames. Moreover, not enough experimental investigation has been done to verify the application of these methods. In this research, a new evaluation method for the collapse mechanism and safety limit of dual structures, which have members with different deformation capacity, was proposed. A shake-table test has been carried out to investigate the applicability of the proposed method to RC buildings consisting of moment resisting frames and shear walls. The test specimen was a 1/4 scale model of a 4-story RC building with multi-story shear walls in both X- and Y-directions. The structure was designed to exhibit a total collapse mechanism (frame-sway mechanism) and so, plastic hinges were designed at the bottom of columns and walls in the first story and beam ends of each story. To investigate the difference of collapse mechanism in the X- and Y-directions, contribution ratio of shear wall to the whole seismic capacity was varied. In the X-direction, two shear walls were placed with the intention of making the failure of shear walls dominate the collapse mechanism of the whole structure (i.e., the failure point of walls corresponded to the global structural safety limit). In the Y-direction, only one shear wall was used such that failure of columns and beams would dominate the global collapse mechanism, which meant that failure of the wall would not correspond to the global structural safety limit. The design concept was quantitatively confirmed based on seismic capacity indices using results of nonlinear pushover analyses. In the shake-table test, scaled artificial ground motions compatible with the Japanese standard spectrum were used as input. The damage of walls preceded in both directions and at the end of the test, the walls were severely damaged and the whole structure was close to collapse. The