Factors Derived from Tests for Fatigue Evaluation of Typical North American Steel Railway Bridges

This article presents the derivation of a static live-load multiplier, alpha (ratio of measured static to simple calculated static), to be applied to the live-load stress range and a rating mean impact multiplier (ratio of average maximum measured impact compared to full calculated impact at various speeds) to be applied to the American Railway Engineering and Maintenance-of-Way Association (AREMA) full design impact for fatigue evaluation purposes of North American freight railway steel bridge spans. These multipliers were derived based on tests of typical North American railway bridge spans conducted by Canadian National (CN) from the mid-1970s to the early 2000s under the direction of the author. Spans tested were subjected to good rail and wheel maintenance typical of North American mainline quality. Roughly 45% of the bridge spans had good-quality continuous jointed rail. Tests were restricted to spans with continuous rail, with adequate either bolted or welded rail joints and without special track work. Different multipliers are presented for three groups: (1) stringers, beams, girders, and floor beams; (2) hangers; and (3) other truss members. Data used in the study were restricted to freight speeds up to 125 kph (80 mph) and spans up to 122 m (400 ft).