Elastoplastic Time History Analysis Of Irregular Plane Isolated Frame Structure

The design of isolation structure in practical engineering mostly assumes that the stiffness of floor in-plane is infinite. The elstroplastic of upper structure isn’t considered, either. In fact, under the rare earthquake, some component of upper structure may enter the plastic. For irregular plane structure, the floor may also enter the plastic. A L shaped practical project with isolation technique, considering the plastic of the upper structure, is studied in this paper. The main work is as follows:(1) According to a small span structure on which the floor has a great effect, model A and model B are set up to be researched. The former considers the effect of floor approximatively according to the current codes. The latter considers the actual section and reinforcement of beam, floor and column.(2) A SAP2000analysis model is established according to the actual section and reinforcement of beam, floor and column. The model for dynamic elastic and elastoplastic time history analysis is studied under three earthquake waves.(3) The upper structure finite element model for dynamic elastoplastic time history analysis is set up to compare with the real model with isolation bearing.Through the above study the following main conclusions:(1)For the small span structure, the rigidity amplification coefficient of frame beam according to the current codes is lower; Under the action of earthquake, the slab reinforcement has adverse effect on the distribution of plastic hinge and the seismic performance; The effect of slab reinforcement should be considered in the seismic analysis and research of practical engineering; The phenomenon of over reinforcement should be avoided in the design of frame beam’s reinforcement. The frame beam’s upper reinforcement could be reduced if possible.(2) After being isolated, the shear coefficient of structure increases with the increase of floor evenly. The range is small and no more than10%. Under frequency earthquake, design earthquake and rare earthquake,64%,43%and38%of the input seismic wave peak acceleration are the peak acceleration of the top structure. With the increase of earthquake intensity, damping effect increased(3) Under design earthquake, the inter-storey drift angle of upper structure is1/558. The upper structure is elastic.Under rare earthquake, the inter-storey drift angle of upper structure is1/216. Some component of upper structure enter the plastic. The plastic hinge is mainly concentrated in the frame beam end.(4) Comparing with the actual model with isolation bearing, the inter-storey shear, inter-storey drift and the peak acceleration of the top structure of the model according to the simplified design method is2.2times of the isolation model. The action increases with the increase of floor. Under rare earthquake the plastic hinge of simple model is more than isolation model. And some column damage. The current simplified design method of upper structure is safe and viable. And there is a lot of security reserve space.(5) Under the rare earthquake, in seismic peak acceleration time, the floor of isolation model and simple model don’t enter the plastic. The floor stress of isolation model is bigger than simple model, which is different from the inter-storey drift. During the design of irregular plane isolated structure, the requirement floor could reduce appropriately. But should be higher than the design requirement of floor with simplified method.