Strengthening of the Net Section of Steel Elements under Tensile Loads with Bonded CFRP Strips

The use of carbon-fiber-reinforced polymer (CFRP) is an increasingly common solution for the strengthening of structures. However, the majority of research and applications have focused on the retrofitting of concrete structures. The applications of adhesively bonded CFRP to enhance the load-carrying capacity of metallic elements has been widely studied in the aeronautical industry, but it is also a promising technique for the area of civil engineering. This paper presents an experimental study that was designed to verify the effectiveness of the use of CFRP for the strengthening of the net section of steel elements under tensile loading. A series of tensile tests were conducted with different bond lengths, number of layers, and surface preparations of the steel. The specimens consisted of double lap joints and steel plates with various hole configurations. The ultimate load, the failure mode, and the effective bond length for CFRP-strengthened specimens were determined. The results showed that using CFRP sheets for the strengthening to prevent net area failure provides no gain on the ultimate strength, a small gain at the elastic limit, and a larger gain if the designer accepts extending the limit state from the elastic limit to the debonding limit.