A Numerical and Experimental Study on Fatigue Life of HFMI-treated Cover Plates in Steel Bridges

Paper in proceeding, 2026

There are a lot of bridges in Sweden that need to be upgraded and strengthened due to heavier traffic. One common method to strengthen existing steel bridges is the addition of cover plates to various bridge elements. Welded cover plates are avoided due to their poor fatigue performance. To mitigate this issue, high frequency mechanical impact (HFMI) treatment is suggested. 3-point bending fatigue tests were done to investigate the effect of weld size and stress range on fatigue life of HFMI-treated welded cover plates. The effective notch stress method was employed to analyze the stress concentration factors at the weld toe and root. Two case studies (5-mm and 7-mm weld throat size) were numerically analyzed and compared with experimental tests. The numerical results are in good agreement with experimental tests. It was found that the weld throat size plays a significant role in the stress distribution at the weld and thus on the failure mode (toe or root cracking) of welded details. Two different failure modes, toe and root cracking, were observed.