EVALUATION OF SIMPLIFIED LOAD MODELS FOR FATIGUE ASSESSMENT OF RAILWAY STEEL BRIDGES

Abstract

The network of Indian rail is among the largest in the world and bridges form a crucial link in the network . assuring continuity of the track across natural and man made obstacles. The performance of bridges being critical to the network necessitates rigorous analysis and design for both static and dynamic loads. It is also necessary that the bridges be assessed for fatigue performance. Most codes for fatigue assessment recommend assessment based on passage of trains or the passage of simplified load models across the bridge. The fatigue provision in Steel Bridge Code (SBC) of Indian railways is under revision and therefore it becomes imperative that simplified load models embodied in there from static consideration be assessed with regarded to their adequacy from fatigue consideration. Typical Plate Girder Bridges (of spans 12.2m, 18.3m and 24.4m) and Welded Truss Bridge(of spans 30.5m, 45.7m and 61.0m) of the Indian railways have been analyzed using SAP 2000 for Modified Broad Gauge (MBG) and Heavy Mineral (HM) trains. Further, the bridges were analyzed for the passage of simplified load models as recommended in SBC on the basis of maximum shear and moments. Analytical results indicate . that the Equivalent Uniformly Distributed Load (EUDL) as recommended by SBC is inadequate for short span Girder bridges and the vertical and diagonal members of Welded Truss Bridges. Simplified load models need to be developed for MBG and HM loadings respectively, along the same lines as the as the other International Codes.