| The seismic isolated design makes the vibration frequency of the engineering structure far away from the characteristic frequency of the soil,which reduces the input of the earthquake energy.Meanwhile,certain types of isolation device such as leadrubber bearings(LRB)can also dissipate the seismic energy and further reduce the response of the superstructure.Since the seismic isolation technology has been incorporated into relevant chapters,the isolation technology has been widely accepted and applied by engineers because of the good anti-seismic performance of the isolation structure.As one of the effective means to resist earthquake,isolation technology has been applied to many important projects such as high-rise buildings,long-span bridges and nuclear power stations.With the wide application of the isolation structure,the demand for the corresponding earthquake risk assessment is becoming more and more urgent,which provides important basis for post-earthquake loss assessment.For the existing methods of fragility analysis for base isolation structures are inefficient or inaccurate,in this paper,the time domain explicit method is applied to the fragility analysis of base-isolated structures,which has the advantage of high accuracy high efficiency compared with traditional methods.The mechanical properties of the isolation bearing have a great influence on the response of the base isolation structure,so the uncertainty of the parameters of the isolation bearing needs to be taken into consideration in the fragility analysis.In this paper,the uncertain parameters of the isolation bearing are regarded as interval variables,and the envelope of the fragility of the base isolation structure is obtained by combining the combination of the combined method with the explicit time domain method in the interval analysis.This study has completed the following work:(1)Summarized the conventional methods of fragilility analysis,such as regression analysis method,probability demand model,response surface method and generalized polynomial chaos expansion method,and analyzed the computational characteristics of these methods.(2)Considering the nature of non-stationary stochastic process excited by earthquake,it is more reasonable to use random vibration method to carry out fragility analysis,and get accurate results.The random vibration theory is applied to the fragility analysis,and the time domain explicit method is applied to analyze the fragility of the non-isolated structure.(3)In view of the base isolation shear structure,the corresponding explicit response iterative formula is derived,and the fragility analysis method based on the explicit random simulation in time domain is proposed.Firstly,the explicit reduceddimension iterative formula for solving local nonlinear motion equations is established;Secondly,obtain the first excursion probility of interlayer displacement and isolation layer displacement by random simulation;Finally,the fragility curve of isolation design is obtained by considering different ground motion intensity.The calculation results show that the proposed method has the same computational accuracy and higher computational efficiency compared with the traditional Monte Carlo method,which greatly reduces the calculation work and improves the calculation efficiency of the fragility curve accurately through random simulation,and is beneficial to the engineering application of the fragility analysis of isolation design.(4)The influence of uncertain parameters of the isolation bearing(initial stiffness,yield stiffness and bearing size)on the fragility of isolated structures is studied.According to the requirements of the design specification and the related support experiment,the uncertain parameters of the isolation bearing are considered as interval variables.The simplified endpoint combination method and the time domain explicit random simulation method are used to solve the vulnerability curve of the interval distribution design,which is convenient for engineering application. |
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