DEFORMATION OF END CROSSBEAMS OF STEEL BRIDGES RELATED TO SUSTAINABILITY OF BRIDGE JOINTS

Abstract

Both AASHTO and Eurocode stipulate that the deflection of end crossbeams of bridges must be limited to 5 mm under the influence of frequent traffic loads. After a thorough literature review and survey of data from manufacturers of bridge joints, it must be concluded that the background of this requirement is not really based on facts. Durability of bridge joints certainly does not appear to be the basis. Another valid reason can be the comfort of road user, which is effectively disturbed by driving over bumps and thresholds. Although the road user expects light shocks at the end of a bridge, the acceleration inside the vehicle must be limited. Therefore, the state of a wheel driving over a threshold has been studied, by applying analytical equations taken from literature and extended. These allow a fairly accurate simulation of the state. Force required to cross the threshold produces an acceleration of wheel, which is transmitted to vehicle's sprung chassis. In the latter one finds the acceleration to which persons are subjected. Several values of comfort can be considered. It turns out that 5 mm limit is very conservative, and one could easily allow up to double the end cross beam’s deflection.