Fatigue Enhancement of Category E' Detailsin Steel Bridge Girders Using CFRP Materials

Abstract

Carbon Fiber Reinforced Polymer (CFRP) composite overlay elements were developed to improve the fatigue performance of Category E' steel details. By increasing the stiffness of the detail with the CFRP overlay, the stress demand at the weld is reduced, resulting in an increased fatigue life of the detail. The CFRP overlays were also designed to be tough enough to resist internal crack growth and delamination due to shear stress from applied loads. Development of the CFRP overlay elements is described, including material testing, finite element modeling of the composite overlay behavior, and a finite element parametric study to investigate relative effects of CFRP element properties. Fatigue testing of steel specimens stiffened with CFRP overlay elements is also described, with bond thickness between the steel and composite materials varied. Results showed that the CFRP elements are robust enough to resist both internal and bond degradation when tested at a stress range of 138 MPa (20 ksi), and can significantly extend the fatigue life of welded details. Modeling results showed that the stress range at the welded joint can be significantly reduced by application of the CFRP overlay element. While a good bond was maintained, crack initiation was effectively eliminated in coverplated specimens. Bond tenacity was investigated and recommendations for achieving good bond based on materials and thicknesses investigated are described.