EPA-based Seismographic Research Of The Input Energy Spectrum

Compared with other seismic design methods,the energy method can better capture the nature of the structural response,and can also better explain the structural damage and other damages caused by earthquakes.However,at present,the seismic design for engineering structures based on the energy method for the whole designing process is yet to mature.And the site types,seismic wave samples and sample sizes studied by different researchers are quite different and lack representativeness,which leads to a gloomy situation,that is,conclusions of relevant studies vary vastly.Moreover,a consensus is yet to reach on input energy spectrum calculation formula for the SDOF system.Therefore,it is imperative to produce more samples,which will be further combined with the established seismic experience and current site categorization standards in China.In this way,an input energy spectrum calculation formula with greater goodness for fit and applicability may be achieved.Therefore,the work and conclusions of this paper are as follows :(1)Analysis of ground motion data and establishment of input energy spectrum.Programs are written to read and calculate(based on energy balance formula)a large amount of ground motion data collected from the PEER database of macroseism.Time-distance curves and energy spectra are obtained to show the energy produced in an elastic SDOF system(0.05 damping ratio)experiencing seismic waves from different sites.Then input energy spectra are analyzed.The result shows that with a higher degree of softness of soil,all energy curves gradually move to the long-period portion.(2)Fitting of input energy spectrum based on EPA and analysis on energy dissipation spectrum.The input energy spectra of four sites are re-classified.The effect of EPA is taken into consideration and the mean spectra of each group are divided into four sections.Consequently,four-segment formulas with better goodness for fitting are obtained..Moreover,the effects of different damping ratios on energy dissipation are analyzed.The result shows a decrease in the damping energy curve value near the peak where the damping ratio is increasing.But in the long period portion,it shows the opposite.(3)Analysis of elastoplastic input energy spectrum based on EPA.After the conversion of four-segment formulas of input energy spectra of the elastic SDOF system,input energy spectra of elastic SDOF system is obtained.The result is checked based on the bilinear hysteretic model with an enhancement coefficient of 0.2.This is basically in line with the result of actual calculation using specific ground motion data,which testifies the feasibility of the converted inelastic four-segment input energy spectra.