Analysis and Comparison of Eurocode and Snip Traffic Load Models for Railway Bridges

Abstract

The traffic loads and consequently the load effects in the bridge structures determined according to the Eurocode (EN) have been found to be substantially different from the values obtained by the SNiP code model used in Lithuania. For highway bridges the SNiP loads are lighter (sometimes 1,5-2,0 times), for railway loads they are considerably heaver. It was decided to investigate whether railway bridges designed to EN and SNiP load models have sufficient capacity and how to achieve good agreement between the load effects determined according to both codes. In this article the results of comparison for simply-supported bridge decks with span lengths ranging from 2 to 80 m. are presented. Rail traffic load models from EN and SNiP are analysed. The objective of the study was to modify the Eurocode rail traffic load factors to fit them to the SNiP loading provisions and to determine the consequences for bridge supestructures, if the bridges were designed according to the code SNiP and assesed according to the Eurocode. It is shown that the actions imposed on bridges of 10-40 m length of spans (that is common in Lithuanian practice) due to rail traffic according to the EN code are 20-40 % lower than those determined according to the SNiP. The EN code gives even five traffic load models in comparison with only one load model in the SNiP. However the effects of load model SW/2 are sometimes lower than those calculated by LM71. The recommendations are presented how to adjust the loading models for both codes in order to insert the specifications of loads on bridges in new national Annex actually in preparation for Lithuanian standard LST EN 1990/A1:2006 lt.