This paper presents the flexural cyclic behavior of I-shaped hot rolled steel deep sections used as beams in moment-resisting frames (MRF) featuring a carbon fiber reinforced polymer (CFRP) patch on the web through advanced finite element analysis. The main goal of the CFRP reinforcement is to increase the rotation capacity of the member without increasing the overstrength to avoid compromising the strong column-weak beam condition in MRF. A reduced finite element model of a steel beam is developed and validated with experimental data. The CFRP patch is modeled considering fracture in the adhesive layer using the cohesive zone modeling (CZM) technique that can capture the crack initiation and propagation. Different adhesive types are investigated where the CZM parameters are calibrated from high fidelity fracture mechanics tests that are thoroughly validated in the literature. This includes a rigid adhesive commonly found in the construction industry and two tough adhesives used in the automotive industry. The results revealed that the CFRP patch can increase the rotation capacity of a steel member considerably when using tough adhesives.

The use of the brittle adhesives commonly adopted in construction industry do not provide the best performance for steel structures. CFRP/Steel joint bonded with extremely tough adhesive achieve much higher strength and ductility. However, tough adhesives are not developed for the construction industry and their cost may question the feasibility of this repair solution. This paper presents a new high performance and cost-effective hybrid bi-adhesive CFRP/Steel joint by using an extremely tough adhesive in critical location and the brittle adhesive in the remaining areas of the adhesive layer. The role of the tough adhesive in the proposed joint is fundamentally different from previous bi-adhesive joint proposed in the literature as it contributes mainly in shear. Experimental testing and finite element analysis are conducted. The Digital image correlation (DIC) is used to measure the strain field on the CFRP. The results revealed that the proposed CFRP/Steel hybrid joint achieve higher strength than the joints with brittle adhesive. The use of the tough adhesive in the bi-adhesive joint reduces the concentration of shear stresses significantly. As little quantities of the tough adhesive are required to manufacture the proposed bi-adhesive joint, it deemed to be as cost-effective.

Recent experimental studies showed that deep steel I-shaped profiles classified as high ductility class sections in seismic design international codes exhibit low deformation capacity when subjected to cyclic loading. This paper presents an innovative retrofit solution to increase the rotation capacity of beams using bonded carbon fiber reinforced polymers (CFRP) patches validated with advanced finite element analysis. This investigation focuses on the flexural cyclic behaviour of I-shaped hot rolled steel deep section used as beams in moment-resisting frames (MRF) retrofitted with CFRP patches on the web. The main goal of this CFRP reinforcement is to increase the rotation capacity of the member without increasing the overstrength in order to avoid compromising the strong column-weak beam condition in MRF. A finite element model that simulates the cyclic plasticity behavior of the steel and the damage in the adhesive layer is developed. The damage is modelled using the cohesive zone modelling (CZM) technique that is able to capture the crack initiation and propagation. Details on the modelling techniques including the mesh sensitivity near the fracture zone are presented. The effectiveness of the retrofit solution depends strongly on the selection of the appropriate adhesive. Different adhesive types are investigated where the CZM parameters are calibrated from high fidelity fracture mechanics tests that are thoroughly validated in the literature. This includes a rigid adhesive commonly found in the construction industry and two tough adhesives used in the automotive industry. The results revealed that the CFRP patch can increase the rotation capacity of a steel member considerably when using tough adhesives.