Composite Patch Configuration and Prestress Effect on SIFs for Inclined Cracks in Steel Plates

The fatigue life of steel bridges can be extended by externally bonding carbon fiber-reinforced polymer (CFRP) patches to the damaged elements to arrest the crack propagation. In this paper, the influence of the patch pretension level, stiffness, and fiber orientation on the stress intensity factor levels are investigated. A three-dimensional finite-element model of the double-sided CFRP patch-strengthened specimen is used to study the fracture behavior of an inclined edge crack under different combinations of loading Modes I and II. The introduction of a compressive stress by pretensioning of the CFRP patch prior to bonding produced a significant reduction of up to 70% in stress intensity factors (SIFs) for different crack lengths, which led to increasing the remaining fatigue life of the steel member. The increase in the CFRP patch-to-steel axial stiffness ratio reduced the SIFs by up to 30%. The optimum benefit of using the CFRP patch to reduce mode I SIF was accomplished when the patch axial stiffness was about 50% of or below the steel plate stiffness. Furthermore, orienting the fibers perpendicular to the crack direction is not necessarily the most effective in arresting the crack propagation. The effectiveness of the fiber orientation in the composite patch depends mainly on both the loading direction and the crack inclination angle. (C) 2016 American Society of Civil Engineers.