The effect of geometry dimensions on fatigue life of HFMI-treated cover plates

Journal article, 2025

One common method to strengthen existing steel bridges is the addition of cover plates to various bridge elements. Currently, using bolted connections is preferred to welded due to the poor fatigue performance of welded connections. The use of HFMI treatment to increase the fatigue strength of welded cover plates is investigated so that welding is used instead of bolting, which will have considerable savings in terms of site work and costs. This study explores how the geometry of beams and cover plates affects the fatigue life of welded cover plates in steel bridges, particularly those treated with HFMI treatment. The effective notch stress method was employed to analyze the effects of cover plate thickness, flange thickness, and weld throat size on the stresses at the toe and root of welded cover plates. Based on the results, expressions were developed to calculate stress concentration factors at the toe and weld root for various beam and cover plate dimensions. It was found that the weld throat size plays a significant role in the stress distribution at the weld and thus on the fatigue life of welded cover plates. Furthermore, the presence of shear stress at the weld toe increases the stress concentration factor at the root, making the weld root more susceptible to root cracking. Evaluating our experimental tests and previous tests in the literature indicates that HFMI treatment significantly enhances fatigue life at the weld toe; however, if the weld root deteriorates faster than the toe, HFMI treatment becomes less effective.