Deriving the Seismic Action for Alternative Return Periods According to Eurocode 8

摘要

The state of practice for major infrastructure projects (e. g. major suspension bridges, LNG plants etc) is to define multi-level seismic design criteria. Unfortunately, Eurocode 8 only presents data to allow a single level of criteria to be defined. The bridges section of Eurocode 8 (EN 1998 - 2) does present a methodology for deriving the seismic action (A_(gR)) for different return periods. A formula is provided which is dependent on an exponent k. The code states "...the value of the exponent k depends on the seismicity of the region. Normally, values in the range of 0.30 - 0.40 may be used...", but no definitive data for the appropriate value of k in regions of low, moderate or high seismicity is provided. This paper will present the development of the appropriate value for exponent k dependant on the 475 year value of A_(gR). The study is based on a more than fifty probabilistic seismic hazard studies carried out by Arup, in regions of low, moderate and high seismicity throughout the world. This development will allow Eurocode 8 to be used to define multiple level performance seismic design criteria, where the National Annex does not provide the necessary information. This will be particularly useful in the early stages of major projects before the development of a site specific hazard assessment.