Normalized Response Spectra And Regression Analysis Of Near-fault Ground Motions

In the field of earthquake engineering, the damage and collapse of engineering structures under near-fault ground motions and their unique characteristics attract the attention of the scholars. In the recent several great earthquakes, the researchers collected a lot of near-fault ground motion records, which provides the convenience for studying the properties of ground motions and their structural effect. This paper calculates the maximum displacement, acceleration and energy responses of bilinear SDOF systems subject to near-fault records, and analysis the change of normalized response spectra and inelastic velocity ratio spectra. Moreover, the regression analysis between the intensity measure parameters of near-fault ground motions and seismic response of bilinear SDOF systems is conducted. The main contents are listed as follows.Firstly, the Northridge and Chi-Chi150near-fault ground motions are taken as the seismic input, and inelastic displacement response spectra, acceleration response spectra and normalized energy response spectra are acquired. The influence of ductility coefficient and pulse type on the displacement and acceleration response spectra is investigated. Numerical results show that, the pulse type and ductility coefficient have significant affect on inelastic acceleration response spectra and displacement response spectra of SDOF system(μ=2,4,6,8). Furthermore, for the dimensionless period of T/Tm and T/Tgi(Tm and Tgi are the mean period of Fourier spectrum and improved characteristic period, respectively), the difference between the normalized input energy spectra under Chi-Chi ground motions with and without velocity pulses is small, and that of Northridge ground motions with and without velocity pulses is smaller. It means that the unified formulation can represent the normalized input energy spectra under impulsive and non-pulse near-fault records which is beneficial to simplify the engineering seismic design.Secondly, the constant ductility and strength inelastic velocity ratio (IVR) spectra under near-fault ground motions are computed. The ductility coefficient, strength reduction factor and damping ratio yield remarkable effect on the IVR spectra. The influence of Chi-Chi ground motions with and without velocity pulses on IVR spectra is larger, while the influence of Northridge ground motions with and without velocity pulses on IVR spectra is smaller. In addition, the effect of frequency content parameters on inelastic velocity ratio spectra is quite small.Finally, this paper introduces the index of local accuracy, and adopts the neglected polynomial regression models, as well as analyzes and evaluates the fitting function and goodness between the intensity measure parameters of near-fault ground motions and seismic responses of bilinear SDOF systems. Comprehensive comparison of regression analyses indicate that the fitting results between them are related to the type of ground motions with and without velocity pulses and the chosen intensity indices, and also associated with the natural periods of system as well as the adopted regression models. According to the fitting results, the better intensity parameters for near-fault ground motions can be identified. Moreover, the quadric polynomial function can satisfy the accuracy requirement of regression analysis for seismic design of structures. This work provides a help for the ground motion selection and fragility analysis of structure.