Research And Application Of The Target Spectrum In Strong Motion Records Selection

With the development of the strong motions observation techniques, the accumulations of the strong motions data have played a great role in the development of structural seismic design theory. The dynamic time history analysis method is required to be used as a necessary complement to the static design method, especially for high-building, large span structures, other special structure or important project. However, there is no detailed specification on the selection of the strong motion records.The strong motion records selected by the designers lack the theoretical basis. The parameter of structural responses is too discrete.In this paper, the strong motion records are collected. The empirical formula of the correlation of the spectrum is improved, which is used to determine the conditions mean spectrum. Based on the ground motion attenuation relation, the relationship between seismic information and seismic design parameters has been proposed. The standard spectrum in the seismic codes is not suitable as a target spectrum. Two methods to deriving the target spectrum are proposed. One is PGA target spectrum based on the attenuation relationship of ground motion. The other is EPA average target spectrum based on the strong motion records. The selection and application of the strong motion records in seismic safety evaluation work are studied in this paper.The main contents are as follows:1. The data of the ground motion records are collected, and the correlations between ground motion parameters are analyzed statistically. Based on the 20 thousands records, the change trend of the boundary periodic point of the correlation of the peak value and response spectrum is found. Based on the site, the adjustment empirical formula of correlation coefficient is proposed, which improves the site characterization of the target spectrum.2. Based on the peak ground motion acceleration(PGA) attenuation relationship, a relationship of the fault distance and the seismic design group is derived, which becomes the primary conditions of the selection of the ground motion records. The analysis of the correlation between the structural responses and the response spectrum show that it is significant around the structural natural period. The farther distance, the correlation coefficient is smaller. The basic principle of matching target spectrum of standards is as follows: the first, refer the distance and the site. The scope of matching target spectrum is determined by the structural natural period, such as 0.4T1-1.5T1. Records are selected according to the mean square error. The scale coefficient of the time history of records is limited from 0.2 to 4.0.3. A reasonable target spectrum in line with seismic requirements is studied. For the project site, when there is no earthquake information of seismic safety evaluation, We propose a reasonable target spectrum which is established by ground motion attenuation relationship. Determine the magnitude and distance by the peak acceleration attenuation relationships. Then, based on the acceleration response spectrum attenuation the spectrum corresponding to the target PGA is obtained. The mean of those response spectrum is the PGA target spectrum. On the basis of the strong motion records, the target spectrum spectral shape and distribution is matched. The target spectrum has the form of a mean and standard deviation. The characteristics of the distribution of the target spectral response express the uncertainty of ground motion. The structural response distribution has a reasonable range.4. This paper proposes a method to establish the EPA mean target spectrum, according to the type of sites and distances to grouping strong motion records data. By the comparison of the EPA target spectrum with standards spectrum of codes, it shows that the EPA mean target spectrum has a more realistic spectral shape. When the standards spectrum of codes is used as the target spectrum of strong motion records selection, the following advices are recommended: 1. Increase the characteristic period. 2. Reduce the value of the long-period response spectrum of 1/2 groups of seismic design and I / II site. Both target spectrums have nothing to do with the structure dynamic characteristics. It is broadly applicable to various structures.5. Methods and principles of the selection of the ground motion records are propesed based on the SHA. Suggestions are as follows:(1) To I level evaluations of sites, the primary condition is identified based on the scenario earthquake. The site design spectrum is taken as the target spectrum, and is matched to selecting records.(2) To II and III level evaluation, conditions mean target spectrum method is taken. The acceleration response spectrum value of the structure is as a condition. Conditions target spectrum is established as the target spectrum,which is matched to selecting records.(3) To IV level evaluation of sites, according to the target PGA values, PGA target spectrum is taken as the target spectrum.