Analytical approach for improving damage equivalence factors

Keywords: Damage equivalence factors Fatigue load model Equivalent length Weigh-In-Motion Traffic load model Monte-Carlo simulation a b s t r a c t The fatigue design of bridges under variable amplitude traffic loads is not straightforward. To simplify the task, the current Eurocode provisions apply fatigue load model 3 and damage equivalence factors (k). However , the fatigue load model and the damage equivalence factors have several shortcomings: (1) the critical span length is defined for limited bridge influence lines, (2) the damage equivalence factors neglect simultaneous presence of several heavy vehicles on bridges, and (3) the safety margin of damage equivalence factors is not uniform for all bridge influence lines. The current study identifies the effective parameters in the damage equivalence factors through a step-by-step analytical approach. Based on the analytical studies, new propositions for two main parameters of the fatigue load model and fatigue equivalent length are made. These modifications not only improve the accuracy of damage equivalence factors (both k and k max) but also extend the application to any bridge influence line. In addition, the proposed modifications are generalized by introducing a partial damage equivalence factor (k 5) which takes into account the effect of repetition in influence lines. The proposed parameters are justified with traffic simulations for various bridge cases. Fatigue is a major parameter in the design of bridges, and bridge design codes usually have specifications for safety verification against fatigue. The fatigue check of a new bridge is complex since it requires the knowledge of traffic loads during the entire life of the bridge, while load assumptions can be made, the engineers still have the work of doing damage accumulation calculations [1]. The concept of damage equivalence factor for a predefined fatigue load model is proposed by the Eurocodes [2,3] as well as the SIA codes [4,5], to express the traffic actions with equivalent stress range at two million cycles and to compare with the resistance of a detail. It is commonly used due to its simplicity, though very few researches [6,7] have been carried out to evaluate its accuracy. The shortcomings of damage equivalence factors can be summarized as follows [8–10]: the definition of fatigue equivalent length is limited, and it does not allow for treating all bridge influence lines; the effect of simultaneity in which several trucks stand on a bridge simultaneously is neglected; the k factors obtained for different bridge …