Proposed design guidelines for strengthening of steel bridges with FRP materials

This paper focuses on the use of externally bonded high modulus carbon fiber reinforced polymer (HM CFRP) materials to strengthen steel bridges and structures. Proper installation of the CFRP materials is necessary to prevent premature failure due to debonding. The paper proposes guidelines and installation techniques based on the best practice reported in the literature and the extensive practical experience in bonding of composite materials. The surface preparation of the materials, the application of the adhesive and the detailing of the strengthening are provided in detail. The design guidelines include the structural design criteria for the use of high modulus CFRP materials as flexural strengthening system of typical steel–concrete composite bridge girders. The flexural design procedure is based on a moment–curvature analysis and a specified increase of the live load carried by the bridge to satisfy specific serviceability requirements. A bond model is also described which can be used to calculate the shear and peel stresses within the adhesive thickness. To prevent a premature debonding failure of the strengthening system, the criteria specify a maximum principle stress in the adhesive which cannot be exceeded for a given characteristic strength of an adhesive. A worked example is presented to illustrate the proposed flexural design approach. The research findings conclude that high modulus CFRP materials provide a promising alternative for strengthening steel bridges that can be easily designed and installed to increase their strength and stiffness.