Static Load-Bearing Capacity Formulation for Steel Tubular T/Y-Joints Strengthened with GFRP and CFRP

Abstract Based on full-scale experiments on steel tubular T/Y-joints wrapped with FRP, nonlinear finite element (FE) models were verified and calibrated for prediction of the static load-bearing capacity (SLC) of FRP-strengthened joints. The verified FE methodology was utilized to perform parametric studies. Due to the fact that local buckling of the chord member is the governing mode of failure in tubular joints capacity, FRP strengthening on the chord is determining while brace strengthening showed negligible effects. Increasing the brace-to-chord diameter ratio (β), chord diameter-to-thickness ratio (γ), and brace inclination angle (θ) enhanced the joint capacity but decreased the FRP effectiveness on the joint capacity improvement. Based on the results of the experimentally-verified numerical analyses and parametric studies, three indices ψ, λ and δ were introduced as strengthening index, FRP fibers orientation and the stacking sequence, to represent the effective parameters respectively. Multiplying these indices by the unstrengthened joint capacity constitutes a practical and efficient formulation for estimating the SLC of FRP strengthened joints. Since a large number of FE models were generated and analyzed, the presented formulas can be employed for FRP optimal application on tubular joints, while providing a guideline for the assessment of the strengthened joint SLC.