Analysis On Pounding Responses Of High-rise Connecting Structures With Flexible Joints Under Earthquake Excitations

In recent years, with the diversity development of architectural form and based on the use functional requirements of the single building, many single buildings are connected with large span steel truss at the top or in the middle, forming the connecting buildings with one or two layer corridors. The early connected form was rigid, but for large-span connecting structure with rigid form, a great temperature stress could be created in the connecting truss due to the temperature changes, and the rigid connection will increase translation-torsion coupling seismic response of the structure under earthquake excitations. In order to solve these problems recently, some experts have taken a new attempt on connection form and designed some new project examples with flexible connection. The flexible connection mainly refers to the elastic bearing connection between the tower building and the corridor; which can effectively reduce the temperature stress and translation-torsion coupling seismic response of the connected structure under earthquake excitations. But it also brings some new problems, such as, pounding between the connecting body and the towers, the collapse of the corridors under strong earthquake excitation. In this paper, based on a long-span flexible connecting structure with multi-towers, in which the connective bearings include pin and elastoplastic bearings, the pounding responses of the connecting structures with flexible joints under rare occurrence earthquake excitations are studied by nonlinear time history analysis method, mainly as follows:1. In genernal, the number of elements of connecting buildings with multi-towers is larger, elastic dynamic analysis is not possible on the ordinary PC, let alone the nonlinear time history analysis. Thus, it is necessary to simplify the tower model. First, the top elastoplastic displacements of single tower are obtained by elastoplastic time history analysis software EPDA under the rare earthquake action; secondly, based on the principle that the elastic displacemetns of towers are equal to the elastoplastic displacements under the same rare earthquake action, reduce the elastic modulus of concrete of towers. finally, towers after modulus reduction are made with sub-structure condensation, generating super-element. Then the number of computing units can be greatly reduced and the computational efficiency can be significantly improved. Due to the corridors truss are steel structure; it can be simulated directly by using elastoplastic beam element without any simplification.2. The equivalent linearization is used to simulate the elastoplastic hysteresis loops of the flexible connecting bearing, and the corresponding equivalent stiffness and equivalent damping of the bearing are obtained.3. The maximum displacement of bearings are obtained by nonlinear time history analysis under 6 degrees rare earthquake excitation, and the maximum displacement can be considered as the critical gap of the pounding.4. Considering the unpredictability of the earthquake intensity, the peak accelerations of earthquake are amplified by 1.5 times or 2 times respectively. The poundings are simulated by KELVIN pounding model, and the dynamic responses of the whole connecting structure in the case of pounding are calculated by the nonlinear time history analysis.5. The analysis results of pounding response show that the direction of the internal forces of the connecting truss caused by pounding is consistent with the direction of the internal forces caused by gravity when the pounding occurred in the upper part of the corridor, and the internal forces are amplified, but the interal forces direction are opposite when the pounding occurred in the lower part of the corridor, so the interal force are reduced. Therefore, the damage of the corridor structure is more serious when the pounding occurred in the upper part. Because the connection building of computation example include pin joints and elasto-plastic connection bearing, and the connection bearings have certain stiffness and damping, the rebounding after pounding do not cause a large opposite displacement in flexible connection bearing. So the corridor collapse can be avoided if the bearings of connection buildings are properly designed under strong earthquake excitations...