| How to select strong motion records is always the most concerned problem for engineers in the seismic analysis of structures.So far,there are no unified understanding on how to select strong motion records in China and abroad.At present,there are three main methods of selecting ground motions:(1)Real records having the same source,path,and site properties as the design earthquake.(2)Artificial earthquake records with specific mathematical models to meet the requirements.(3)Semi artificial earthquake records which use the real records as "seeds" to meet the requirements by adjusting their Fourier amplitude spectrum.However,the first type of ground motion record is rare,which makes it difficult to select such records..The artificial earthquake records lack some important information of nature properties.Semi artificial earthquake records combine the advantages of real records and artificial records.These kind of records not only maintain the nonstationary character of real records,but also match the target spectrum.Code for seismic design of urban bridges and Specification of seismic design for Highway Engineering in China,and the seismic design of the California Transport Department of the United States clearly stipulate that this semi artificial strong earthquake records can be selected.Although some of the codes for seismic design in our country suggest this semi artificial strong motion records,it has not been applied in other codes.Therefore,this paper uses the method of adjusting Fourier amplitude spectrum to match the strong motion records suitable for various codes under different conditions,and analyzes the application of this method in various codes.This paper's main work and conclusions are as follows:(1)Three basic approaches for spectral matching are introduced,including scaling method,frequency domain method(adjusting the Fourier amplitude spectrum based on the ratio of the target response spectrum)and time domain method(adding wavelets to the initial records directly).In addition,the advantages and disadvantages of these methods are compared.Among them,the scaling method is a simple linear method.The frequency domain method is suitable for the entire target spectrum matching.SeismoMatch software is suitable for spectrum matching with a specific period.(2)The current various codes for seismic design in China are introduced,including Code for seismic design of buildings(GB 50011-2010),Code for seismic design of urban bridges(CJJ 166-2011),Code for seismic design of hydraulic structures of hydropower project(NB 35047-2015),Specification for seismic design of special structures in petrochemical industry(SH 3147-2014),Code for seismic design of special structures(GB 50191-2012),Specification of seismic design for highway engineering(JTG B02-2013),Code for seismic design of petrochemical steel facilities(GB 50761-2012).We compared the target spectra of each code and the regulations of design ground motion records.The requirements of these codes for the design ground motion recodes can be summarized as follows:the design ground motion recodes are not less than three groups,either real records or artificial earthquake records can be selected.(3)By adjusting the Fourier amplitude spectrum of initial records to match target spectrum of each codes.The appendix gives the design strong motion records of each codes under different site types,different fortification intensities,different earthquake effects and different design earthquake groups.What we found are as follows:The shorter the period of the target spectrum is,the faster the computation speed is.And the mean relative error of Code for seismic design of petrochemical steel facilities is obviously higher than that other codes.This shows that the longer the period of the target spectrum is,the worse the matching precision is.(4)A new method for selecting ground motion records that can match the target spectrum for mean spectrum of multiple sets of records is proposed in this paper. |
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