CALCULATING BRIDGES FOR THE ACTION OF A WEAK (DESIGN) EARTHQUAKE.

According to Russian standards calculating bridges is made only for the action of a strong (maximum design) earthquake with a frequency of once every 500-5000 years. In the whole world practice there is a transition to multi-level designing, which considers several structure limit states and the corresponding design actions. The paper discusses the features of such transition in relation to bridges, with the whole range of issues related to such calculations being described. These issues include specifying limit states, specifying the level of design action, setting load combinations and design schemes for bridges, and taking into account damping in bridge elements. The developed proposals require setting the allowable repeatability of certain limit states and are based on the instrumental part of the current the seismic scale standard.