Repairing Distortion-Induced Fatigue in Steel Bridges Using a CFRP-Steel Retrofit

Abstract

Distortion-induced fatigue (DIF) cracking in steel bridges accounts for one of the most common types of fatigue damage in steel bridges in the United States. Many methods have been developed to repair DIF; however, most available repair methods require concrete deck removal, which is expensive and disruptive to traffic. This paper describes an experimental study aimed at investigating the fatigue behavior of steel bridge girders repaired with a novel CFRP and steel retrofit. The retrofit addresses an important need in repairing distortion-induced fatigue - creating a load path from the connection stiffener to the girder flange without requiring bolting or welding to the flange. To evaluate the performance of this combined retrofit, fatigue tests were conducted using a half-scale 2845 mm (9 ft) long steel girder-to-cross-frame subassembly. The girder was cyclically-loaded to produce realistic DIF crack patterns, then a retrofit that engages three surfaces: the web, the flange, and the connection plate, was added. Five trials are described; two of the trials were performed in the unretrofitted condition while the other three trials were performed in the retrofitted condition. The retrofit performance was examined for different crack patterns, up to a 4 in. crack length. The experimental results showed that the CFRP-steel retrofit was effective in preventing distortion-induced fatigue crack propagation for all the tested crack patterns and lengths.