FRP wrapping for the rehabilitation of Circular Hollow Section (CHS) tubular steel connections

• Steel tubular connections could be effectively rehabilitated with FRP material.
• FRP composite had a remarkable contribution in stress reduction on the steel substrate.
• Confining action of the FRP had increased steel ductility and hindered plastification.
• FRP through thickness stress distribution revealed the saddle points to be critical
• Matrix failure in compression was the governing criteria in FRP damage assessment.
• Failure of FRP initiated at relatively high proportions of the ultimate load.

This paper presents the results of a numerical and experimental research program conducted on T and Y shaped steel tubular connections made of Circular Hollow Sections (CHS). Axial compression acting on the brace member and consequently on the chord face at the intersection was selected for the monotonic loading regime. Numerical models for six connections consisting of two T-shaped and four Y-shaped connections were generated using ABAQUS software package. Three of these connections served as reference without any reinforcement. The three others were identical connections strengthened with FRP. A displacement controlled non-linear static analysis was performed in which post-peak behavior of the connections was captured. Moreover, six test specimens were designed and fabricated based on the experiment configuration. The specimens were reinforced by uni-directional glass fibers impregnated with vinyl ester resin and wrapped all around the intersection of the members and the adjacent areas. A typical putty material was also incorporated at the intersection prior to placement of the FRP to avoid wrinkles and sharp edges at the corners. The load–displacement and load–ovalization behavior, state of strains, stresses and deflections were recorded on selected portions of the connections during the experiments. Steel and composite failure mechanisms were also studied. Assessment of the relative studies showed that the FRP wrapping had significant influence on the ultimate load capacity of the connections and had proven to highly improve connection behavior. In addition, contribution of the FRP wraps in load bearing and assisting the steel substrate to moderate the effects of such loading prior to failure initiation was remarkable.