Abstract
A structural reliability evaluation is performed of the current AASHTO fatigue specification for steel bridges. The reliability model incorporates uncertainties in vehicular loading, analysis, and fatigue life. Field data is obtained from a weigh‐in‐motion system, which utilizes existing bridges as equivalent static scales. The load data includes truck axle and gross weights, headways, impact, stress range, girder distribution, and volume. A fatigue life model is formulated in terms of a fatigue failure function. Using the loading and fatigue life data a safety index is calculated using a level II reliability program. The study reviews the current specification in order to derive uniform reliability levels over the range of typical designs. The proposed revisions include: (1) A design vehicle model more representative of the current U.S. truck population; (2) changes in allowable stress ranges to eliminate variations in safety index; and (3) a range of load factors to represent site specific truck volume and loadometer (weights) values. These recommended changes lead to more uniform safety levels and fatigue lives for steel bridges.
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