Graphical abstract Load, P, vs. mid-span displacement, Δ, for un-strengthened (control) steel beam and steel beams strengthened with 50 mm wide (full width) Ultra-High Modulus (UHM) CFRP laminate, 10 mm Strips Panel, and 5 mm Strip Panel. Display Omitted

Highlights • Steel beam strengthened with the 50 mm wide UHM CFRP laminate failed in rupture. • Failure load for 50 mm UHM CFRP strengthened beam was 39% larger than control beam. • Two beams strengthened with 5 mm & 10 mm UHM CFRP strip panels failed in debonding. • Failure load for 10 mm UHM CFRP strip panel beam was 27% larger than control beam. • Failure load for 5 mm UHM CFRP strip panel beam was 26% larger than control beam. • Steel yielding was not detected prior to failure in all UHM strengthened beams.

Abstract Strengthening of steel beams utilizing FRP material has numerous advantages over traditional methods, which include bolting or welding new steel plates to the existing structure. Compared to other FRP material, Carbon FRPs (CFRPs) have been preferred for strengthening steel due to their higher stiffness. The emergence of High Modulus (HM) and Ultra-High Modulus (UHM) CFRP laminates, with an elastic modulus higher than that of steel, enables an increase in load transfer in steel beams prior to yielding of steel. Earlier research has highlighted the premature debonding failure of splice plates when used with UHM CFRP laminates. As an alternative to using a splice plate/laminate, this study investigates the performance of CFRP strip panels. The panels are designed so that continuity between two consecutive panels can be achieved through a finger joint. The panels are fabricated using narrow UHM CFRP strips (e.g., 5 mm, 10 mm) mounted on a fabric mesh, which is designed to maintain the necessary clear spacing between individual strips. Flexural tests are carried out under 4-point bending on steel wide flange beams. A 50 mm wide UHM CFRP laminate strengthened beam without laminate splicing is compared with the novel strip panel type splice strengthened girders. Two different strip widths of 5 mm and 10 mm are tested and all beams, strengthened with the same CFRP area, are evaluated against an un-strengthened control steel beam. The failure of the steel beam strengthened with the 50 mm UHM CFRP laminate was due to laminate rupture at a failure load (PFU-50mm) that is 39% larger than the load at which yielding initiated (Py) in the un-strengthened control beam (PFU-50mm = 1.39 Py). The tensile strains observed during rupture were 30% higher than the average maximum tensile strain observed in the material tests. The beams strengthened with UHM CFRP strip panels failed in debonding at the finger joint, with failure loads that are 27% and 26% larger than Py for the 10 mm and 5 mm strip panels respectively (PFU-10mm = 1.27 Py, PFU-5mm = 1.26 Py).