Design of Steel Beams Strengthened with Low-Modulus CFRP Laminates: Fid-Bau Portal

Design of Steel Beams Strengthened with Low-Modulus CFRP Laminates

Selvaraj, Sivaganesh / Madhavan, Mahendrakumar

This paper presents an analytical study to investigate the ability of low-modulus ( $< 150 GPa$ ) carbon fiber–reinforced polymer (CFRP) laminates to strengthen steel beams. Although the need for retrofitting structural elements is high in South Asian countries, the nonavailability of high-modulus CFRP led to the use of low-modulus CFRP in this investigation. The aim of this study was twofold: (1) to understand the behavior of structural members strengthened with low-modulus CFRP; and (2) to suggest an appropriate limit state to predict the design strength of the CFRP-strengthened member. Four-point bending experiments were carried out to examine the behavior of CFRP-strengthened steel beams. In general, the governing failure mode of steel beams strengthened with low-modulus CFRP was intermediate debonding. The occurrence of intermediate debonding was due to the large difference in moduli of steel and low-modulus CFRP. The design predictions indicated that the use of the ultimate strain design limit state suggested by current design provisions is unconservative compared with the experimental results. Therefore, based on the failure mode observed in the experiments, two new design limit states were introduced to determine the ultimate design strain; the first is conservative, up to the elastic strain of steel beam (elastic strain limit state), and the other is up to transition point of low-modulus CFRP (transition strain limit state). Such conservative design limit states are suggested to prevent the debonding failure between CFRP and steel beams. The design and reliability analysis results indicated that the newly introduced limit states (elastic strain and transition strain) are suitable for the design of steel beams strengthened with low modulus CFRP.