Fatigue Damage Factor Calibration for Long-Span Cable-Stayed Bridge Decks

Part 2 of the Eurocode 3 (EN 1993-2) proposes a straight forward fatigue verification method using a single heavy vehicle model (FLM3) and a damage equivalent factor, lambda, to represent the fatigue damaging effects of the real traffic on road bridges. The method is very appealing for bridge design. However, the lambda-factor has limitations and is not defined in the EN1993-2 for some load cases or "span lengths" above 80 m, renamed here as "critical lengths". This is the case of cable-stayed bridge decks, where a combination of two internal forces-bending and compression (induced by the stays)-is a characteristic of this bridge system, and stay-cables, with specific shapes of influence lines. To address the above issues a variant solution of the Vasco da Gama Bridge is taken as the case study. In this paper, the results of the lambda-factor computed for different critical lengths are compared with previous studies and the original work that led to the current EN formulas for lambda. Based on these results, a constant lambda value for critical lengths above 80 m is proposed to update the EN for the "mid-span case". For the fatigue design of stays and steel girders, recommendations are given for determining the critical length based on the influence line of the bending moments.