Study On The Order Of Strong Earthquake Ground Motion In Term Of The Intensity Of Damage To Structures

Since the San-Francisco earthquake occurred in the United States in 1906,after more than 110 years of efforts,great progress has been made in modern earthquake engineering.The Long Beach earthquake(M_w=6.3)occurred in the Los Angeles area of the United States on March 10,1933.Scientists used accelerometers to record the first historic ground motion acceleration record(ground motion record)in the world.Hundreds of thousands of ground motion records have been collected all over the world in the past hundred years.These records provide a wealth of ground motion data sets for structural seismic design.At present,the most commonly used method for selecting input ground motion is based on the target spectrum matching method:design spectrum,uniform hazard spectrum,conditional mean spectrum and so on.But the destructive strength of many ground motion records to the structure is also different.The seismic capacity of structures varies greatly when different input ground motions are selected in seismic design.However,there is still an unsolved problem for earthquake engineering scientists and engineers all over the world:how to scientifically evaluate the destructive effect of ground motion on engineering and how to compare and order a large number of strong motion records according to the strength of engineering damage.In this paper,based on the theory of the most unfavorable design ground motion,the destructive strength of the ground motions from the most unfavorable to the most favorable is researched,the strong ground motion records are ordered according to the destructive strength,and the destructive strength of the ground motion records is combined with the transcendental probability.The recommended design ground motion records with different strength levels are given based on the transcendental probability.The specific research contents in this paper are as follows:(1)For the selection of ground motion database and ground motion parameters.The existing database is widely analyzed,and the data characteristics,coverage and other factors of each database are analyzed.The NGA-West2 database is selected for analysis,and the ground motion records are divided into four categories according to the site classification standards of our country.In this paper,17 commonly used ground motion parameters are widely selected to represent the characteristics of ground motion time-history,and the ground motion parameters are simplified through correlation analysis.Finally,six representative ground motion parameters,PGA,PGV,PGD,D_u,D_b and D_s,are given.(2)The period segments of the structure are redivided based on the improved triple spectrum,and the structure is divided into three types:rigid structure,rigid-flexible structure and flexible structure.it is assumed that the failure mechanism of the same kind of structure is the same,but the failure mechanism of different structures is different.In this paper,the division method of structural period segment is summarized,and two improvements are made based on the method proposed by Xu and Zhao:one is to consider the site factors,and the other is to consider the uncertainty of ground motion.Finally,the division results of structural period segment related to the site type are obtained.(3)The influence of the natural vibration period and yield strength coefficient of structure on the ordering of structural response is analyzed.When the elastic-plastic response occurs in the time history analysis of the structure,the nonlinear degree will change and the period will be prolonged.When the structural parameters change(natural vibration period and yield strength coefficient),the structural response generally changes,but the change of structural response sequencing is not known.Therefore,the influence of the natural vibration period and yield strength coefficient on structural response ranking is analyzed,and it is proved that the natural vibration period or yield strength coefficient has no influence on structural response ordering.(4)Finding out the relationship between the damage action of ground motion and the damage mechanism of structure.In previous assumption,there is a logarithmic relationship between the ground motion destructive strength parameters and the structural damage index.However,the destructive strength parameters representing different structural damages are proposed in this paper based on the Spearman correlation coefficient of the ground motion destructive strength parameters and the structural damage index.(5)Based on the damage index of single degree of freedom(SDOF)structure,the ordering of ground motion according to destructive strength is established.In this paper,the ordering results of unscaled ground motion records and the ordering results of scaled ground motion records combined with the current seismic design codes are given for each type of site and structure,which can provide design ground motions for seismic design.(6)By combining the destructive strength of ground motion with the exceeding probability,the ordering results of different exceeding probability corresponding to the destructive strength is established.In this paper,ground motions with transcendental probabilities of<1%,1%,2%,5%,10%,20%,30%,40%,50%,63.2%,70%and 80%are selected as recommended design ground motion records.