Study on performance of RC frames with casting in-situ slabs under bi-directional horizontal seismic excitation

During the Wenchuan earthquake, many local building structures were suffered huge damage, especially the multi-story RC frames with slabs in which the weak-beam strong-column design philosophy were not realized. The contribution of the slabs can be very important. Current studies focus on pseudo-stastics of connections, pushover analysis and time-history investigation without slabs. Seismic performance of RC frames with casting in-situ slabs under bidirectional seismic excitation has not been reported yet. In order to investigate the influence of floor slabs during earthquake, three FE models are built by ANSYS. These three models are bare frame under bidirectional seismic excitation, frame with slab under unidirectional seismic excitation and frame with slab under bidirectional seismic excitation. Natural period of vibration, cumulative story drift, slabs participation and moment history of the models are compared. The results indicate that the natural period of vibration and the cumulative story drift reduces in frames with slabs. The abnormal and uneven moment equilibrium appears in connections when the participation of the slabs is considered. Compared to unidirectional seismic excitation, slab participation increases with a decrease stress level during bi-directional seismic excitation. The design should be paid more attention.