Study On The Attenuation Of Ground Motion Energy

The structures are generally put into non-linear state under the strong ground motion. In fact, the investigation of earthquake disaster shows that it is true. First, there are inelastic deformations of structures after intensive earthquake. Second, there are permanent deformations of structures after intensive earthquake. Once the structures step into inelastic work state, the earthquake input energy is dissipated by the damp and inelastic distortion. Hence, the energy is the best parameter when a structure is inelastic designed or evaluated for seismic hazard. Presently, the ultimate-state seismic design based on energy has been concerned in the field of earthquake engineering. Based on 266 strong ground motion records from 15 earthquakes in America, an attenuation relationship was used to relate energy spectra to earthquake magnitude, source-to-site distance, and site class. The purpose of this study is to make a foundation of energy-based design and seismic hazard analysis.The main achievements of this study could be summarized as follows:1. Establishment of an improved strong ground motion database.Strong ground motion records, one of the experimental resources for earthquake engineering, have made an important role in earthquake engineering research. Although there are a large amount of strong ground motion records all over the world, for the mass, there are disadvantages such as having no uniform format, short of parameters and so on. So, records from 15 earthquakes in the U.S. are checked in this paper. Especially moment magnitude and fault-distance are added.2. Introduction of concept and calculating method for energy spectra.In ultimate-state seismic design, energy spectra have been used for the reliable indices of seismic motions that determine their influences on structural failure and non-linear response. Also, energy of ground motion can be viewed an index to incorporate the duration effect on structures, because longer duration usually induces a large energy demand. The duration of ground motion is so sufficiently taken into account. The concept and characteristic of energy spectra are introduced in detail in the paper.3. Discussion the two-stage regression analysis method.There is a good relativity between the magnitude and distance. This kind of relativity is inherent and inevitable. If the coefficients of attenuation model were solved simultaneously, errors in measuring magnitude would affect other coefficients. In order to minimize the biased result, a two-stage regression method suggested by Joyner and Boore is used to decouple the dependence of magnitude and distance. In fact, the two-stage regression method has been proved effective to decouple the coupling of the magnitude and distance, and minimize the regression error. The two-stage method, including the weighting matrix important for the stage-two regression, is discussed detailedly in the paper.4. Analysis of the attenuation law of ground motion energy.All records are classified into three site conditions. For the two components of a record, two energy equivalent spectra are calculated, and the geometric mean of the two spectra are adopted to analysis by two-stage regression method using an attenuation model. Then the attenuation law is attained. And the effect, of the parameters such as site conditions, magnitude, ductility and distance on the energy spectra is analysis detailedly in the paper. In order to validate the validity of the result in the paper, the result of Zhou and Uang (2000) is used to contrast with the result. Some important conclusions are made at last.