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This paper consists or three parts. First, fatigue test data are presented for a tensile specimen with transverse stiffeners, a typical steel bridge detail. The specimens were tested under variable-amplitude fatigue for up to 250,000,000 cycles of loading proportional to the gross vehicle weight distribution of 27,000 trucks weighed on highways. Few and, in some cases, no stress ranges exceeded the endurance limit in the longest life tests. It took up to nine months to test the longest-life specimens.
Second, the variable-amplitude S-N life is predicted with an equivalent stress range model in which stress ranges smaller than the fatigue limit are assumed not to contribute to fatigue damage. A simplified S-N model is proposed for determining the fatigue life of existing bridges. The variable-amplitude fatigue limit is shown, both experimentally and analytically, to be a function of the constant-amplitude fatigue limit and the ratio of root-mean-cube stress range to maximum stress range of the variable-amplitude load spectrum.
In the third part of the paper, the variable-amplitude fatigue lives of the transverse stiffener specimens are predicted with a fracture mechanics model of crack growth.
Fatigue, highway bridges, variable amplitude, fatigue limit, steel, design, testing, specifications, overload, stiffeners, welds
Prof., Univ. of Maryland, College Park, MD
Turner-Fairbank Highway Research Center, Federal Highway Administration, McLean, VA