Study On The Methods Selecting And Synthesizing The Ground Motions Matched By Both Acceleration And Displacement Spectra

Ground motion(GM)record is crucial to the structural dynamic analysis.It can demonstrate the failure mechanism and aseismic capacity of structure by means of representative GM records.Therefore,it receives extensive attention from earthquake engineering and civil engineering to the GM selection.Herein,performance-based and resilience-based seismic design up-to-date requires selecting high-quality GM suite for structures.Discussion among researchers on the validity of GM records representing the seismic hazard in future does not terminate since the earthquake is random and the structure may fail in different modes.Moreover,the present seismic codes merely provides simple rule on the GM selection.It may be not robust and cumbersome to increase the GM records when the model is complex or performs in highly nonlinear state.To overcome this weakness,this article proposes a new GM selection strategy which can match the acceleration and displacement design spectra simultaneously.After that,the selected GMs can be modified by introducing acceleration wavelet to improve the spectral matching level.Finally,a new earthquake intensity vector was proposed and used for sampling records minimally but reasonably estimate the structural performance.The main contents include:(1)GM data processing is one of the key problems before the GM selection is done.High-pass filter cut-off frequency is an important parameter which will influence the displacement remarkably.To improve the GM data quality,a new methodology was proposed.Average displacement before P-wave arrival and the ending displacement were chosen as the measure parameters.They were used to measure the displacement change rate with low-cut frequency.By means of the curve angle function and least square method,frequency where the displacement and PGD change rate significantly change can be identified.Accordingly,the cut-off frequency can be detected.Comparison of the results derived from the proposed method were compared with traditional methods in addition to the inelastic displacement spectra and constant ductility strength reduction factor spectra.(2)Displacement spectrum can directly provide low-frequency information of GM record.The consistency of GM records may be enhanced if the long-period displacement spectra are considered in the GM selection.It is because divergence in the long-period acceleration spectra is much lower than that in the long-period displacement spectra.To select GMs both matching the acceleration and displacement spectra,this study adopted the non-dominated sorting multi-objective optimal method to optimally select the GM records.Initial population is generated by the stationary distribution of a Markov chain.Then,better non-dominated sorting population is selected as father population and evolves by selecting the records matching the sub-target acceleration spectra obtained by solving the inverse of multivariate normal distribution.Finally,the maximum response of RCF under the GM records derived by the proposed method and traditional method is compared.(3)Structural lateral collapse capacity estimation is crucial to the PBSD.It is low efficiency to assess the PBSD reliably using traditional GM selection method since numerous records are needed.Basically,response spectrum has nothing to do with the duration even though it reflects the frequency and amplitude of a GM record.Hence,it may be unreliable to predict the collapse capacity of a structure merely based on GMs matching target spectra.Through studying the correlation between the duration and collapse capacity result using the synthetic records in addition the other GM parameters,a new GM sampling method was proposed considering duration and matching both acceleration and displacement spectra.Finally,influence of GM number on 6 RCF structural collapse capacity was illustrated and a minimal GM number was accordingly proposed.(4)It is an effective way to supplement the GM database for dynamic analysis with synthetic records when the GM records are insufficient or the dynamic results are in great dispersion.Synthetic records can be used to analyze the influence of spectral matching on the structural performance estimation in addition to the GM parameters.However,the GM selection method would affect the result of synthetic GM record when the long-period displacement spectrum is not well matched.Displacement baseline drift occurs when the long-period displacement spectrum deviates far from the target spectrum in terms of traditional method.For this,this study proposed a new method based on wavelet package transform technique.Spectrum-compatible synthetic record is generated by re-comprising all decomposed components using genetic algorithm.Finally,the comparison of synthetic and real GM records was presented and its influence on RCF maximum drift,residual displacement and lateral collapse capacity was delineated.