# Fatigue of Steel Beams by Simulated Bridge Traffic

*by*Charles G. Schilling, (M.ASCE), Section Supervisor — Engrg. Mechanics; U.S. Steel Corp., Research Lab., Monroeville, Pa.,

Karl H. Klippstein, Assoc. Research Consultant; U.S. Steel Corp., Research Lab., Monroeville, Pa.,

**Serial Information**: Issue 8, Pg. 1561-1575

**Document Type:**Journal Paper

**Abstract:**

A review of field measurements on bridges under traffic showed that a family of Rayleigh probability-density curves can represent the frequency of occurrence of stress ranges of different magnitudes in actual bridges. A particular histogram for a bridge can be approximated by a particular curve from the family. Each curve is defined by: (1)The modal stress range, S_{r}_{m}; and (2)a parameter S_{r}_{d}, which is a measure of the width of the probability-density curve. Different combinations of S_{r}_{m} and S_{r}_{d} were included. The variable-amplitude data can be related to the constant-amplitude data by using an effective stress range to represent the variable-amplitude spectrum. The effective stress range is the constant-amplitude stress range that would result in the same fatigue life as the variable-amplitude spectrum, and may be taken as the root-mean-square stress range of the spectrum or calculated from Miner's law.

**Subject Headings:**Steel beams | Steel bridges | Traffic models | Curvature | Effective stress | Bridges | Fatigue (material) | Bridge components

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