Performance of steel sections strengthened with carbon fibre reinforced polymer plate under tropical climate

The use of Carbon Fibre Reinforced Polymer (CFRP) to strengthen steel structures has attracted the attention of researchers in recent years. Previous researches demonstrated that bonding of CFRP plates to the steel sections has been a successful method to increase the mechanical properties. However, behaviour of the system under various environmental conditions has not completely been defined yet. The main objective of the study is to evaluate the performance of steel/CFRP bonding system after exposure in natural tropical climate. Environmental conditions including wet/dry cycles, submerging in plain water, salt water and acidic solution were considered to define the effect of different exposures on the system. In the experimental program, double lap shear specimens (DLS) and strengthened I-section steel beams were prepared and subjected to the environmental exposures up to 8 months. Further, CFRP and epoxy adhesive coupons were prepared and exposed to the same conditions to find the influence of aging on the materials individually. Tensile tests and four-point bending tests were performed after exposure and the mechanical properties were compared to the control specimens. The results demonstrated that the epoxy adhesive was the critical part. In addition, the strength and stiffness of the coupons which were subjected to tropical climate showed a remarkable increase around 16% and 11% at the beginning of exposure, respectively. However, these properties were reduced gradually until the end of exposure. The results of tests on DLS specimens and strengthened steel beams indicated the same rate of properties degradation as the adhesive coupons. The failure mode for strengthened steel beams was lateral-buckling which showed the bonding strength was still remained after exposure. Further, the properties of CFRP plate showed negligible changes for all environmental conditions. The theoretical analysis has been conducted to predict the properties of specimens before and after exposure and the results showed close agreement to the experimental tests