Flexural strengthening of steel I-beams using CFRP composites

Abstract

The degradation of construction materials has led to a growing need for the repair and strengthening of existing structures. The use of carbon fibre reinforced polymer (CFRP) for the strengthening of structural members has been expanding in structural engineering due to its advantages and practicality, proving to be highly effective in reinforcing concrete and timber elements. With steel being a widely used material in construction, particularly in large scale projects, interest has been increasing over the combination of these two highly strong and lightweight materials. This research study focuses on investigating the flexural behaviour of steel I-beams reinforced with CFRP composite materials through the experimental testing of five beam specimens. With one of the specimens being used for a control test, thus unreinforced, the other four beams were strengthened with CFRP laminate and wrapping. The first reinforced specimen was simply strengthened with a CFRP laminate bonded to the underside of the bottom flange with epoxy resin structural adhesive, while another specimen was identically strengthened with the difference that the CFRP material was anchored towards its ends to prevent delamination. The remaining two specimens were reinforced in the same manner using CFRP wrap. The four-point bending test was carried out on each beam specimen. From the results obtained, the stress-strain and load-vertical deflection curves, as well as the strain distribution throughout the section were plotted and used to compare the effectiveness of the CFRP reinforcement. Although delamination is the most common failure mode of this strengthening system, all the beam specimens failed through ductile yielding with the CFRP wrap remaining intact and transverse slip of the CFRP laminate being observed at mid-span. Results showed that both reinforcing materials increased the stiffness of the beam and enhanced its flexural capacity, however the CFRP wrap performed better than the CFRP laminate due to better adhesion and load transfer. The enhancement in load-carrying capacity of the specimen with an unanchored CFRP laminate was minimal, approximately 3%, and remained within the same margin with the anchors installed. On the other hand, the beam specimen strengthened with the CFRP wrap registered an increase of around 9%, which almost doubled with the anchoring plates installed towards the ends, giving an improvement of 17% over the control specimen.