Report No.: CCEER-97-1-B

Title: Sensitivity Analysis of Fatigue Evaluation of Steel Bridges

Authors: Prem P. Rirnal and Ahmad M. Itani

Date: September 1997

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557


This report presents the sensitivity analysis of fatigue evaluation for Nevada steel bridges. Parameters affecting applied stress ranges were studied and varied in a three-span four steel plate girder bridge to determine their effect on fatigue evaluation. The allowable stress range parameters were examined to determine their effect on the overall fatigue behavior. The current research and practice of other major state DOTs in dealing with fatigue cracks, evaluation procedures and repair methods were studied and examined.

From the study, it was found that for closely spaced (S < 5.83 ft.) and widely spaced (S > 17.5 ft.) bridges, the 3-D structural analysis gave approximately 50% and 25% higher stress range values than the 2-D analysis respectively. For normally spaced (10 < S < 14 ft.) bridges, the 2-D structural analysis gave 50% higher values. For the case of skewed bridges, the 2-D structural analysis gave approximately 50%, 75%, and 170% higher values of stress ranges than 3-D analysis for 0° , 30° , and 60° skewed bridges, respectively. It was also found that increasing the skew angle, girder spacing and depth will decrease the stress ranges. The applied stress ranges did not vary with the configuration and cross-sectional area of cross frame and lateral bracing. However, as skew angle increases, cross frame and lateral bracing members attracted more axial forces having these location prone to out-of-plane fatigue cracking. The single HS2O Truck was found to be the most damaging load in terms of fatigue life due to its high frequency of occurrence during the life span of a bridge. Over thirty states responded to the questionnaire about fatigue evaluation and repair methods. Many of these responses could be applicable to Nevada steel bridges (Abstract by authors).