A Study On Analysis Approach For Seismic Responses Of Aseismic And Isolated Structures Based On Explicit Time-Domain Random Vibration Method

The response spectrum method and the time-history analysis method,recommended by the Code for Seismic Design of Buildings(GB 50011-2010),can not fully reflect the random effects of seismic excitations on buildings due to the inherent non-deterministic features of seismic excitations.The response spectrum method actually has been found to inaccurately estimate the seismic responses in most cases owing to the assumption of white noise input and equal modal peak factors.For the seismic analysis of isolated structures,the seismic isolating coefficient method recommended in the Code for Seismic Design of Buildings(GB 50011-2010)is dependent on the seismic responses of the non-isolated structure obtained by the response spectrum method.Accordingly,certain errors also can be found between the responses obtained by the code method and the random vibration method in practical applications.Therefore,it has been a great demand to use the real random vibration method to conduct the seismic analysis of aseismic and isolated structures.For this reason,a new approach for the seismic analysis of aseismic and isolated structures has been proposed in this dissertation to improve the seismic analysis methods for these types of structures in the current design codes based on the explicit time-domain approach developed in recent years.The major work in this dissertation is described as follows:(1)The research on the random vibration methods for linear and nonlinear systems is reviewed from the point of view of uncoupling treatment of the physical evolution mechanism and the probabilistic evolution mechanism involved in random vibration problems.Then,the analysis methods for seismic responses of aseismic and isolated structures in the current design codes are introduced.Different types of nonlinear restoring force models and the corresponding equivalent linear models for isolated systems are discussed.Specific attention has been paid to the implementation and existing problems for the seismic isolating coefficient method using in the code of our country.(2)The explicit time-domain method(ETDM)for deterministic structures under nonstationary excitation is elaborated based on the explicit time-domain expression of dynamic response.Using the above explicit expression,mean values and variances of the structure responses at different time points are obtained through the calculation rules of the first order moments and the second order moments.In particular,the ETDM can separate the physical evolution mechanism and the probabilistic evolution mechanism in random vibration problem,so that it provides a fundamental tool for further investigation of the seismic responses of large-scale aseismic and isolated structures.(3)The efficient Monte-Carlo simulation(MCS)based on ETDM is proposed for the random vibration analysis for seismic response of aseismic structure.The calculation principle and the implementation method of the proposed method are clarified for seismic analysis of structures,including the transform method for the equivalent power spectrum of seismic excitations corresponding to the specified response spectrum,the formulation method based on the precise integration method and the Newmark-β integration,the implementation method for the explicit expressions of seismic responses of a structure,and the detailed implementation process for the efficient MCS based on ETDM.(4)The efficient MCS based on ETDM with dimension-reduced iteration scheme is proposed for the random vibration analysis of isolated structure.With the advantage of dimension-reduced representation of the time-domain explicit expressions for dynamic responses of an isolated structure,only those local degrees of freedom related to isolators in the pseudo-linear motion equations are required for nonlinear iterative computation.The proposed method can serve as a high-efficiency random vibration method for nonlinear seismic analysis of isolated structure.(5)The proposed approach is employed to the application to seismic analyses of the aseismic and isolated structure from the point of view of practical engineering.An adjustment approach based on the calibrated storey shear forces obtained by the present random vibration method for the seismic responses of aseismic and isolated structures are proposed to overcome the problem induced by the method recommended by the current design code.Numerical examples and engineering applications show that the proposed random vibration methods for obtaining the random responses of aseismic and isolated structures under non-stationary seismic excitation have good accuracy and efficiency.An effective way to conduct the seismic design based on random vibration theory is provided for the improvement of current design codes.