INFLUENCE OF SSI ON FATIGUE CHARACTERISTICS OF RAILWAY STEEL TRUSS BRIDGES

Abstract

Steel railway bridges are susceptible to fatigue damage under the action of repetitive and yet fluctuating moving train loads. In general, Soil Structure Interaction effects are exempted in detailed fatigue life estimation. The objective of this study is to depict a qualitative picture of SSI effects on fatigue life of railway steel truss bridges. Here, the fatigue characteristics of analytical models of prototype bridges are studied with and without consideration of SSI effects, i.e. with soil springs on pier and Abutment supports, and without soil spring on simple supports. The loading includes two categories of train loadings namely MBG and HM for three types of speeds namely operating, rated and future speed. Moving load analysis without inertia effect to capture time varying response and dynamic analysis with varying speed and damping were performed for all the conditions. Palmgren-Miner linear damage hypothesis is introduced for damage estimation after cycle counting of consecutive stress ranges through rainflow counting algorithm is performed. The methodology employed in this study shows a simple, though efficiently pursuable approach to capture the effects of some crucial parameters for representation of Bridge — Soil system and of fatigue provisions On the basis of observations made in this study, we may conclude that SSI effects are negligible for long span bridges. But for short span bridges and in idealistic un-damped condition, SSI effects can be included in detailed fatigue life estimation especially for abutment supported bridges