Abstract
Emerging as a new technology, carbon fiber-reinforced polymer (CFRP) has been introduced to rehabilitate and strengthen steel structures using an adhesive agent. However, the outdoor service temperature is potentially degrading to the mechanical strength of the adhesive, as well as affecting the bonding of the strengthened steel structure. Therefore, this paper aims to investigate the bond relationship of CFRP-strengthened steel plates exposed to service temperatures. Two types of experiments were conducted to determine the tensile and flexural performance of CFRP-strengthened steel plates. The experiments were designed using a Box–Behnken design (BBD) and response surface methodology (RSM) by considering three parameters: service temperature (25 °C, 45 °C and 70 °C), number of CFRP layers (one, three and five layers) and bond length (40, 80 and 120 mm). The findings show the dominant failure mode transformed from adhesion failure between steel and adhesive interfaces to adhesion failure between CFRP and adhesive interfaces as the service temperature increased. The tensile strength improved by 25.62% when the service temperature increased. Field emission scanning electron microscope (FESEM) analysis proved that the strength enhancement is due to the densification and reduction of the adhesive particle microstructure gaps through the softening effect at service temperature. However, service temperature is found to have less impact on flexural strength. Incorporating the experimental results in RSM, two quadratic equations were developed to estimate the tensile and flexural strength of CFRP-strengthened steel plates. The high coefficient of determination, R2, yields at 0.9936 and 0.9846 indicate the high reliability of the models. Hence, it can be used as an estimation tool in the design stage.
Highlights
The deterioration of steel structures due to environmental exposure means that they are in need of being rehabilitated and strengthened to maintain and enhance structural integrity
In this study, the bond behavior of carbon fiber-reinforced polymer (CFRP)-strengthened steel plates exposed to service temperature were investigated
The dominant failure mode at room temperature occurs between steel and adhesive interfaces, and the dominant failure mode at service temperature occurs between CFRP and adhesive interfaces. 1- In tensile bonding, increases in temperature from 25 ◦C to 70 ◦C increases the ultimate load capacity by 25.62%, 48.79% and 60.71% after strengthening with one, three and five layers of CFRP, respectively
Summary
The deterioration of steel structures due to environmental exposure means that they are in need of being rehabilitated and strengthened to maintain and enhance structural integrity. The conventional retrofitting methods are the external attachment of a new steel plate or replacement with a new steel plate through welding or bolting These methods require heavy lifting equipment, more labor, time for installation and higher fatigue stress and danger, in high-elevation and fire-sensitive environments. When temperature exceeds the Tg at 50 ◦C, the adhesive mechanical properties transform from an elastic glassy state to a rubbery state, which significantly reduces the elastic modulus, stiffness and strength of the adhesive [4,5]. This situation strongly affects the bonding interfaces and adversely affects the bonding performance of CFRP-strengthened steel structures [6]
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