Experimental study on the effectiveness of strengthening openings in two-way reinforced concrete slabs with CFRP sheets

This study presents an experiment on the impact of externally bonded carbon fiber-reinforced polymer (CFRP) sheets in strengthening large openings in two-way reinforced concrete (RC) slabs. Five identical square RC slabs with dimensions of 1200 mm × 1200 mm × 60 mm were fabricated. All the test slabs had a large, centrallylocated opening with dimensions of 400 mm × 400 mm. One slab was an unstrengthened control specimen,while four were strengthened at the opening using CFRP sheets. Two strengthening schemes were studied:CRFP sheets bonded along four sides of the opening and diagonal at the four corners of the opening at 45-degree angles. All test RC slabs were supported on all four sides and subjected to a vertical load applied to the perimeter of the opening. The main experimental results obtained include the load-displacement relationship at the edge of the opening, the cracking pattern and the failure mode of all test specimens. Based on these results, it can be seen that (1) using CFRP sheets to strengthen openings in two-way RC slabs increases the stiffness and load-bearing capacity of the slabs; (2) CFRP sheets bonded perpendicular to the principal stress direction in two-way slabs are more effective than those bonded along the edges of the openings. Additionally, an analytical calculation for the load-bearing capacity of RC slabs with openings strengthened with CFRP sheets was performed. The calculation results closely matched the experimental findings and provided a better understanding of the effect of CFRP sheets in strengthening.