Experimental Fatigue Evaluation of Typical Cross-Frame Details in Steel I-Girder Bridges

Cross-frames, which primarily serve as stability braces in steel I-girder systems during erection and deck construction, are susceptible to load-induced fatigue problems in finished composite structures if not properly detailed. Due to eccentricity in the connections, cross-frames are often subjected to significant in-plane and out-of-plane bending effects that can affect the fatigue resistance. This paper documents the results of a full-scale laboratory study that evaluates the fatigue performance of common welded cross-frame configurations and details. Eighteen unique cross-frame panels, including various typical and proposed connection details, were fabricated and tested for failure under cyclic loading that simulated the effect of live load traffic on composite girder systems. Based on the results of this experimental study, many details that are prevalently used in practice were shown to exhibit poor fatigue characteristics due to (1) the presence of localized stress concentrations near welds and/or (2) significant bending stresses not explicitly considered in analysis and design. Conversely, the proposed details mitigated these effects and were subsequently found to improve the fatigue life of cross-frame systems.