Flexural strengthening of steel bridges with high modulus CFRP strips

Acceptance of carbon fiber-reinforced polymer (CFRP) materials for strengthening concrete structures, together with the recent availability of higher modulus CFRP strips, has resulted in the possibility to also strengthen steel structures. Steel bridge girders and building frames may require strengthening due to corrosion induced cross-section losses or changes in use. An experimental study investigating the feasibility of different strengthening approaches was conducted. Large-scale steel-concrete composite beams, typical of bridge structures, were used to consider the effect of CFRP modulus, prestressing of the CFRP strips, and splicing finite lengths of CFRP strips. All of the techniques examined were effective in utilizing the full capacity of the CFRP material, and increasing the elastic stiffness and ultimate strength of the beams. Results of the experimental program were compared to an analytical model that requires only the beam geometry and the constitutive properties of the CFRP, steel, and concrete. This model was used to investigate the importance of several key parameters. Finally, an approach for design is proposed that considers the bilinear behavior of a typical strengthened beam to the elastic-plastic behavior of the same beam before strengthening.