Seismic Performance Analysis Of Irregularly Super-long Isolated Structure Considering Initial Unloaded Displacemental Isolators

Base-isolate technique has been widely recognized in the industry because of its good damping effect, so it is used as an effective protective measures to protect the building and internal facilities, meanwhile reduce the effects of the earthquake. With the improvement of the isolate technique, the means of theoretical and experimental analysis, super-long isolated structures are increasingly commen. Multi-tower structure with large podium is often used in the irregularly super-long isolated structures. Due to the long plane, temperature and shrinkage of the concrete will cause great stress resulting in cracking even affect the normal usage. However, the isolated structures play isolation effect by smaller stiffness of isolators, when bearing stiffness is relatively supple, temperature stress and concrete shrinkage will produce relative deformation of isolation bearings in the horizontal direction. When non-load deformation produced in the isolators, slightly eccectricity was in isolators before normal usage stage, whether this eccectricity will affect the isolation effect of the irregularly super-long isolated structure under strong earthquake or not, it’s need to be considered and researched further. When isolators deformed, whether seisimic performance will be greatly affected or in the event of strong earthquakes will be easily collapsed, there’s no enough detailed research. Due to the lack of rich research on this, more analyses are needed.Dynamic time-history analysis on the irregularly super-long isolated structure by Italian finite element software SeismoStruct was taken in this paper, and incremental dynamic analysis (IDA) on the irregularly super-long isolated structure subjected to pre-displacenment was taken. Based on these two analyses, analyses of following areas of dynamic effects and collapse resistance of irregularly super-long isolated structures considering pre-displacement:(1) Compared the dynamic response of the irregularly super-long isolated structure with traditional seismic structures under near-fault pulse, near-fault non-pulse and far-field earthquake, and investigated the isolation effect. The results show that under different earthquake and different intensity, the irregularly super-long isolated structure can perform well. Compared with traditional seismim structure, isolated structures can greatly reduce the dynamic response of structures.(2) Considered the influence of different ground motions, compared the dynamic response of irregularly super-long isolated structure under near-fault pulse, near-fault non-pulse and far-field earthquake, to investigate the influence of different ground motion on the dynamic response of the irregularly super-long isolated structure. The analysis shows that the response of the irregularly super-long isolated structure under the near-fault pulse is more obvious, which are related with the ground motion parameters. The greater the peak ground acceleration, the greater the peak ground velocity, the higher the energy input ground motion, the clearer is the dynamic response. Dynamic reponse of the middle tower under different earthquake is less than left and right towers; large energy input can stimulate greater response of upper structure, while ground motion of large spectra displacement can produce greater influence on horizontal displacement of isolators, the higher of the ratio of PGV/PGA, the more significant is the pulse effect of near-fault ground motion, and the more obvious is the horizontal displacement response of the isolation bearings.(3) Considering the initial displacement of isolators, analyze and compare the dynamic response of the irregularly super-long isolated structure under near-fault pulse, and investigate the seismic performance of this non-ideal isolated structure when encountered8degree and9degree rare earthquake respectively. The results show that the pre-displacement can affect the dynamic response of isolation, and the response is different at different locations. Initial displacement of isolators can increase the dynamic response of adjacent layers to isolators.(4) According to the actual project, take nonlinear dynamic time-history analysis by incremental dynamic analysi method to get the IDA curves of structure so that seismic performance can be analyzed. Obtained vulnerability curves based on IDA curves to analyze vulnerability of this non-ideal irregularly super-long isolated structure and to evaluate the seismic performance of the isolation subject to initial diaplacement. The results show that under the same PGA, the upper structure of the middle tower in response is smaller than the left and right towers. Isolator type is different, the IDA curves vary a lot, but curves showed a monotonically increasing trend overall. When20mm pre-displacement and no pre-displacement was in isolators, IDA curves are concentrated in the elastic stage while discreted large in nonlinear stage in left, middle and right towers. The more extended the IDA curves of different types of bearings under earthquake, the distribution is more scattered. Damage value corresponding to IDA curves of isolator type of GZY500is the maximum. In the near-fault earthquake, especially in the pulse-type ground motion, the damage value of upper structure and isolators are larger. Analyzed vulnerability based on the IDA curves, the analysis shows that when there is initial displacement in isolators, compared with non-displacement isolators, irregularly super-long isolated structure still has well seismic capability when encountered8degree and9degree rare earthquake, and isolators still can perform well.