Rehabilitation of notch damaged steel beams using a carbon fiber reinforced hybrid polymeric-matrix composite

The retrofit of notch damaged steel beams is investigated via the experimental testing of nine wide-flange steel beam specimens and finite element simulation. Three notch configurations representing various damage levels were identified, and the beam specimens were retrofitted using carbon fiber reinforced polymer (CFRP) laminates and a recently developed Carbon-fiber Hybrid-polymeric Matrix Composite (CHMC) that has been termed CarbonFlex, and that exhibits superior energy dissipation and ductility properties. The peak-load deflections of the CarbonFlex-retrofitted beams were calculated to be between 67.8% and 73.1% higher than their CFRP-retrofitted counterparts. The results are attributed to the substantially higher damage tolerance of CarbonFlex than conventional carbon-fiber reinforced polymer. Finite element models were developed to investigate the damage mechanism and loading carrying capacities of the beams, and the strain/ stress distributions near the notch tips. The numerical results match closely with the experimentally determined load-deflection curves and the strain fields obtained by the digital imaging correlations (DIC) technique. Both experimental and numerical results clearly indicate the effectiveness of CarbonFlex, as a candidate retrofitting material, for damaged steel structures. Lastly, the micro-mechanisms by which CarbonFlex could sufficiently sustain a significant amount of the peak strength at large deformations are discussed through scanning electron microscopy (SEM) and nano-indentation studies.