The Effect Of Slabs On Strong Column-weak Beam Mechanism Of RC Frame Structures

In Wenchuan Earthquake, one of the major failure modes of frame structures is the strong beam-weak column mode, which illustrates that the strong column-weak beam mode required by the Chinese seismic code fails to realize. One of the main reasons is that the effect of slabs is not appropriately taken into account. Because of the complexity of frame-slab interaction, the slab is often assumed to be rigid, approximatively considering the influences of slabs on frame beam stiffness. However, the influences of slabs on frame beam strength is neglected in structural design and analysis. This simplified approach is impractical, and leads the major failure mode of the frame structures to plastic hinge mode in column. Because such damage is enormous, it is necessary to research the effect of slabs on the performance of frame structures.In response to the failure phenomena that reinforced concrete frame structures fail to realize the strong column-weak beam yield mechanism, this study assesses the influences of slabs on structural seismic performance. The main contests are as follows.1) According to the experimental and theoretical analysis, the effect of slab on the seismic performance of frame structures is analyzed.2) The finite solid element models of frame with and without slabs are established. By using static lateral loading method, the strength and stiffness properties on both kinds of frame structures are compared. By observing the scope of participation of slab reinforcements in bending beam ends at different lateral drifts, the effective width value of the slab is proposed.3) Depending on different column-to-beam strength ratios, the RC frame structures with and without slabs, which designed with the Chinese seismic code, are established. The top displacement, story drift and the distribution of plastic hinges under rare earthquake are studied with dynamic time history analysis. The reasonable column-to-beam strength ratios are obtained.4) Through the above analysis, some improved suggestions for ensuring the strong column-weak beam yield mechanism required by the Chinese seismic code in frame structures are presented, and some useful conclusions are given.