The Dynamic Amplification on Highway Bridges due to Traffic Flow P.H. Rattigan, E.J. OBrien, A. Gonzalez Dept. of Civil Engineering, University College Dublin, Earlsfort Terrace, Dublin 2, Ireland. Tel: +353 1 716 5575 Fax: +353 1 716 7399 mailto:paraic.rattigan@ucd.ie Domain: Dynamic loading Technical areas: Bridge engineering, civil engineering Abstract: It is important in the design of highway bridges that adequate consideration is given to the level of bridge excitation resulting from the dynamic components of a bridge-truck interaction system. The concept of a dynamic amplification factor (DAF) is used to describe the ratio between the maximum load effect when a bridge is loaded dynamically, and the maximum load effect when the same load is applied statically to the bridge. The Eurocode, EC1, Part 3, stipulates that a generalised DAF value be applied to the worst static load case for a given bridge. This worst static load case can be obtained by using Monte Carlo simulation to create a site-specific traffic load model based on weigh in motion (WIM) data. For a medium span 2-lane bridge, this worst load case may consist of two heavy 5-axle truck meeting at, or close to the mid-span of the bridge. However this approach is inherently conservative as the DAF is provided based only on a few general parameters that ignore many significant bridge and truck dynamic characteristics (in particular, in the Eurocode the dynamic amplification factor depends on two parameters: bridge length and shape of the influence line). As a result, unnecessary rehabilitation or replacement costs may be incurred. In recent times research has been carried out into improving vehicle models, road surface models and numerical models for the bridge-truck dynamic interaction. It is hoped to advance the knowledge of the dynamic interaction between bridges and crossing trucks using a finite element approach, whereby different load cases and simulation of critical load events can be carried out, using complex models. Thus a more representative and site-specific value for DAF may be obtained. 1. Introduction The Eurocode normal traffic load model for bridges is derived by applying a Dynamic Amplification Factor (DAF) to the worst static case obtained from extrapolating load effects using free flowing traffic simulations and weigh-in-motion data. In the Eurocode, the theoretical value of DAF for a particular bridge depends on the shape of its influence line and one single variable, i.e., bridge length (O’Connor 2001). Since this method does not take into