Retrofitting of steel beams using low-modulus carbon fiber reinforced polymer laminates

A feasibility study on the use of low modulus (<125 GPa) carbon fiber reinforced polymer (CFRP) in the retrofitting schemes of structural steel beams subjected to flexural loading is presented. A various CFRP wrapping optimization methods were introduced namely tension flange strengthening and U-wrap strengthening. The result indicates that the strength of the member can be increased significantly by adopting the appropriate wrapping method. A simple theoretical calculation to estimate the design moment capacity of the CFRP strengthened steel member with the nonlinear material properties has been presented. Further, the design stress and strain values recommended in the current design provisions of ACI were validated with the test results and found to be unconservative. Therefore, a method to evaluate the design strain of a strengthened structural steel member using low modulus CFRP has been suggested from the present results. The reliability study based on the limited test results also indicates that the suggested elastic strain design limit state is reliable. For ease of understanding, a design example for predicting the design strength of the steel flexural member strengthened using low modulus CFRP has been provided.