Analysis On Multi-Dimensional Seismic Response Of Rubber Bearings Base-Isolation Structure

The application of isolation technology is quite related to the study of the mechanical model and the seismic response analysis theory for isolated structures. So far. many objective factors such as natural characteristics of ground motions and spatial characteristics of structures are ignored by adopting simplified plane models and basic assumptions for convenience. Intensive studies on structural seismic responses under multi-dimensional earthquake excitations are carried out in this paper, based on summarizing researches of scholars at home and abroad. The main contents and conclusions are as follows:Firstly, according to the mechanical properties of laminated rubber bearings (LRBs). several common restoring force models are summarized, and their own characteristics and limitations are analyzed. Base on the comparison of several common structural calculation models. LRB is considered as a special element, and the storey shear model is employed as dynamic analysis model for isolated structures, also the corresponding assumptions and simplifications are proposed, then the kinematic equation is established and dynamic time-history analysis on structures are performed combined with numerical methods.Secondly, taking a seven-storey base-isolated structure for example, seismic responses of the structure under one-directional, bi-directional, and tri-directional earthquake excitations are compared, and the effects of multi-dimensional earthquake excitation on the isolated structure are studied by changing structural stiffness and introducing seismic response ratio coefficient. The results show that the seismic response of the structure is not only effected by the first mode but also effected by higher modes, and it has high nonlinear characteristics in translational process. Multi-dimensional earthquake excitation has a significant influence on structural dynamic response, compared with that under one-direction excitation. Both under one-directional ef and multi-dimensional earthquake excitations, hysteresis curves of isolation bearings are plump, which indicate that the bearings have good capacity of energy dissipation. Hysteresis curves under multi-dimensional excitation are very irregular compared to those under one-directional excitation, due to the coupling of mechanical properties in two directions. Further studies show that, effects of multi-dimensional earthquake excitations on the three indicators, such as acceleration response, isolation-layer displacement and storey shear force, of seismic responses are different with those of one-directional excitation. Therefore, the effect of multi-dimensional excitation should be paid more attention during design process.Lastly, effects of main parameters, including spectrum characteristic, acceleration amplitude of ground motion, input direction of ground motion and parameters of the isolation layer, from the aspects of ground motion and isolation layer, on multi-dimensional seismic responses are analyzed. Responses under one-direction excitation are compared with those under bi-directional and tri-directional excitations. The results show that both spectral characteristic and acceleration amplitude have remarkable effect on multi-dimensional seismic responses, while the influence of duration is slight under certain conditions. The input direction of ground motions is one of the important factors, seismic responses under bi-directional excitation increase with increasing input angle compared with those under one-directional excitation. Lateral stiffness of isolation layer has a significant influence on the displacement of isolation layer in X direction, the increase rate of displacement ratio under bi-directional excitation to one-directional excitation is obviously, especially if structural natural vibration periods hit a certain extent. The base shear force in X direction has similar characteristic. The yield force of isolation layer Qjand the scale factor r have remarkable influence on seismic responses, their trends are complex, but there are optimal values.In summary, in this paper, restoring force model and multi-dimensional seismic response analysis theory are studied systematically, and influence factors of multi-dimensional seismic response are analyzed, all these will provide certain references to analysis theory and calculation method on base-isolated structures.