EXPERIMENTAL STUDY ON PANCAKE COLLAPSE OF RC SPACIAL SLAB-COLUMN STRUCTURES UNDER EARTHQUAKE

Shaking table tests were conducted for two three-story spacial slab-column structure models with weak stories. The El-Centro (NS) earthquake record was used to produce the excitation and its peak acceleration increased gradually until the pancake collapse of the weak story occurred. Horizontal accelerations were recorded for all stories before and after the occurring of pancake collapse. The vertical accelerations induced by the pancake collapse were also recorded for the floor slabs of the weak story and the story just below. Model M-2 had more weight than Model M-1. Test results show that: 1) with the increasing of the seismic damage degree, the models’ torsional responses increased; 2) the fundamental frequencies of Models M-1 and M-2 prior to the occurring of pancake collapse were only 8.9% and 4.7% lower than their initial values respectively, indicating that it may be impractical to use the change of frequency to predict structural collapses; 3) intensive fluctuation occurred in a very short time period for the horizontal acceleration of each story due to the pancake collapse; and the maximum absolute accelerations of Models M-1 and M-2 during the fluctuating period were in a range of 5g~10g, 5~20 times larger of M-1’s and 10~50 times larger of M-2’s maximum absolute accelerations respectively; 4) the vertical accelerations of the weak story floor slab and the floor slab just below the weak story induced by the pancake collapse were in a range of 30g～40g.