Shear reinforcement of steel I-beams using CFRP composites

Abstract

This dissertation presents a comprehensive investigation into the strengthening of steel I-beams using carbon fibre-reinforced polymer (CFRP) materials. Steel I-beams are widely utilized in various structural applications due to their high load-carrying capacity. However, in certain cases, such as increased loading demands or structural degradation, the existing I-beams may require reinforcement to enhance their structural performance. In recent years, CFRP materials have emerged as a promising solution for the retrofitting and strengthening of steel structures. The objective of this research is to evaluate the effectiveness and feasibility of CFRP strengthening techniques for steel I-beams. The study encompasses experimental testing, and analytical models to assess the structural behaviour, load-carrying capacity, and overall performance of CFRP-strengthened I-beams. This would be ideal over existing strengthening procedures in locations were due to health and safety issues together site restrictions welding would be prohibited. Laboratory experiments were conducted to investigate the mechanical properties of CFRP materials namely SikaWrap® - 600, as well as their bond behaviour with steel surfaces using epoxy Sikardur® - 300. Six configurations of CFRP installation were used to understand their respective structural performance in relation to a control beam; namely CFRP bonded 1) to the web only in a vertical orientation (i.e., perpendicular to the flanges); 2) to the web and on the radii of the beam in a vertical orientation; 3) all around the beam in a vertical orientation; 4) to the web at 45°; 5) to the web and on the radii of the beam at 45°; 6) all around the beam at 45°; to a 6” x 3” recycled S235 I-beam of length 1.3 m under four-point bending. Vertical and diagonal orientation configurations increase the shear area of the web of the steel section by 140 mm2 and 170 mm2, respectively. It was shown that 1.2 mm CFRP strengthening material has the potential for enhancing shear strength at yield by a minimum of 21.42% (for configuration 1) and up to a maximum of 37.5% (for configuration 4). This upper limit enhancement would be equivalent to welding a 2.8 mm S275 steel plate using EN 1993-1-1:2006 guidelines. These findings underscore the potential of CFRP as an effective method for shear strengthening. Moreover, CFRP offers the added benefits of efficiency, not requiring heavy lifting equipment or specialized tools. The outcomes of this study will contribute to a deeper understanding of CFRP strengthening techniques for steel I-beams and their potential for enhancing structural integrity. The research findings will assist engineers in making informed decisions regarding the implementation of CFRP strengthening strategies, leading to improved load-carrying capacity, enhanced durability, and extended service life of steel I-beam structures.