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 tha...

Fiber-reinforced polymer (FRP) overlays have been successfully used in the aerospace industry to repair fatigue damage in aluminum plates. With this success there is potential for use of similar FRP overlays to repair fatigue damage in aging steel bridge structures. This study investigated the effectiveness of repairing fatigue damage in steel plate with adhesively bonded carbon fiber–reinforced polymer (CFRP) overlays. A total of 15 steel plate specimens with preexisting fatigue cracks were repaired with varying thicknesses of CFRP overlays to evaluate the effect of the ratio of axial stiffness of the composite to that of the underlying steel, the axial stiffness ratio (SR), on increased fatigue life and decreased applied stress. The results showed that increasing the axial stiffness ratio from 0 to 0.4 could increase the fatigue life by a factor of 10 for the most extreme conditions, and with an optimal axial stiffness ratio infinite fatigue life may be reached. Fatigue life of the steel specime...

This study evaluates the performance of various methods to prevent and repair fatigue damage in welded connections, a recurring problem that affects a significant number of steel bridges. Experimental tests and analytical simulations were carried out to investigate the fatigue performance of coverplate specimens in which the welded connections were reinforced with carbon-fiber reinforced polymer (CFRP) overlays. Specimens were loaded in three-point bending induced by a cyclic load to evaluate the change in fatigue-crack initiation life of the welded connections caused by the attachment of the CFRP overlays. Test results showed that when bond between the CFRP overlays and the steel was maintained, the reduction in stress demand was sufficient to extend the fatigue life of the welded connections from AASHTO fatigue-design Category E’ in the unreinforced configuration to the infinite fatigue life range. Test results also showed that the fatigue strength of the bond layer was drastically improved by i...