Designed accelerograms for the direct dynamic method of determining seismic loads
To calculate the seismic stability of objects by the direct dynamic method of seismic loads, computed accelerograms for specified constructing site are required. The article shows that the use of accelerograms, which do not take into account the soils amplification properties of the particular study site, can lead to incorrect engineering calculations of the seismic resistance of buildings. The article considers the question of how different the maximum acceleration at the same input motion (in the form of an accelerogram) at different sites located close to each other is. The results of modeling the amplification of one and the same input motion by the soil strata of two different sites are presented. The sites have a similar geological structure. The bedrock is at the same depth. Geographically, the sites are located at a distance of 10 km from each other in Kiev on the right bank of the Dnieper. Under such conditions, when designing seismic resistant objects, design engineers for emergency load combination calculations usually use the same set of design accelerograms. The modelling results presented in this article showed that the soil amplifications of the same input motion, even closely spaced and, at first glance, sites with similar geological structure, may differ significantly. This discrepancy is due to the diversity of soil conditions and the characteristics of the seismic wave propagation in them, that is, the filtering seismic properties of soils. The use of calculated accelerograms, which do not take into account the filtering properties of soils at a particular site under study, leads to incorrect engineering calculations of the seismic resistance of buildings. The article shows that accelerograms should be calculated only taking into account the filtering properties of soils for specific sites of the proposed seismic resistant construction, which will achieve the required seismic resistance while reducing the cost of the object.
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