FRP-steel bond study of IM and UHM CFRP strips

Prior research has highlighted the premature debonding failure in spliced Ultra High Modulus (UHM) CFRP laminates. This study is the initial step in developing an alternate to spliced laminates by introducing CFRP strip panels that provide continuity through a finger joint between two consecutive panels. The panels are fabricated using narrow CFRP strips (e.g., 5 mm) mounted on a fabric mesh designed to preserve the required clear spacing between individual strips. The objective herein is the determination of the bond strength and development length for the individual strips in the finger joint. Initially, an estimate of the development length for both Intermediate Modulus (IM) and UHM CFRP laminates is derived from tests conducted on steel plate specimens doubly reinforced with CFRP laminates. Tests on double lap shear specimens, for both IM and UHM CFRP, were carried out to derive the bond characteristics for the 50 mm wide laminates and the 5 mm and 10 mm wide CFRP strips. The laminates and the strips have the same thickness. The development length was 50 mm and 75 mm, and the bond strength was 1.9 kN/mm and 3.0 kN/mm for the IM and UHM CFRP strips (both 5 mm and 10 mm), respectively. These findings will be used in future studies to develop a “finger joint” that connects the CFRP strip panels to form a continuous externally bonded reinforcement. The experimental results showed that CFRP strips having a low CFRP strip to steel width ratio have higher bond strength per unit width when compared to both IM and UHM CFRP and 50 mm wide laminates.