Fatigue Enhancement of Welded Details in Steel Bridges Using CFRP Overlay Elements

Abstract

Carbon-fiber reinforced polymer (CFRP)-overlay elements were developed with the purpose of enhancing the fatigue performance of welded connections in steel bridge girders. Fatigue tests of seven specimens, including four CFRP-strengthened specimens and three control specimens, were performed to quantify the effect of the CFRP overlays on the fatigue crack initiation lives of the welded connections. Results showed that bonding of CFRP overlays significantly reduced the stress demand on welded connections tested at high stress ranges, leading to a large increase in fatigue crack initiation life. The level of effectiveness of the CFRP-overlay elements in extending the fatigue crack initiation lives of the tested connections was found to be affected primarily by bond strength under cyclic loading; bond strength was found to be dependent on the composition and thickness of the resin layer used to bond the CFRP to the steel. With the AASHTO fatigue design curves as a frame of reference, it was found that when an optimal bond composition was employed, reinforcing the welded connections with CFRP overlays led to a change in fatigue performance category from that consistent with Category E to runout at high stress ranges. An optimal bond composition was identified that resulted in excellent performance under fatigue loading.