Shaking table test and numerical simulation on a vertical hybrid structure under seismic excitation

A shaking table test of a 12‐story steel/reinforced concrete (S/RC) frame, which is composed of a 4‐story steel frame in the higher part, a 1‐story S/RC frame as a transition story in the middle part, and a 7‐story reinforced concrete (RC) frame in the lower part of the model, has been conducted, and its results are compared with those of a standard 12‐story RC frame to evaluate seismic performance of this S/RC frame. The numerical simulation on such hybrid frame structure has been performed and validated by the above experimental results. It is found that irregular lateral‐stiffness distribution along structural height will not only increase rotation at the joint of boundary between transition story and steel frame or concrete frame but also enlarge rotation at such joint and lead to more obvious rigid deformation in steel frame of S/RC frame, which will undoubtedly intensify bending failure. Meanwhile, acceleration response of the upper steel frame will reach its peak when characteristic site period is near the counterpart of the upper steel frame. Further, the maximum interstory drift under frequent earthquake excitation is at the lower substructure, namely, the RC frame, but this is not the case in rare earthquake situation. When it comes to determining damping ratio for vertical hybrid structure, a general method for engineering, which takes concrete and steel damping ratio for the whole structure analysis and then gets envelopes of these results for design, may yield conservative results. Meanwhile, such method may underestimate responses near the transition story.