Study on mechanical properties of circular compression members strengthened by T steel welding: Experiments and FEA

To investigate the influence of T steel welding reinforcement on the mechanical properties of circular tube compression members, this study conducts experimental and numerical simulation research. Nine specimens were designed, with variables including 3 or 4 T steel pieces, weld interval lengths of 400 mm/600 mm, continuous welding, and under load welding conditions. DIC technology, strain gauges, and a horizontal loading device were used to test the mechanical responses, while corresponding finite element models were established. The results show that the ultimate capacity of reinforced members increased from 19.45 kN to over 53 kN, and the failure mode transformed from middle-span bending instability to instability failure combined with horizontal torsion of T steel (for T3 series) or instability failure combined with horizontal bending (for T4 series). Initial imperfection is a key influencing factor: Specimens T4 exhibited more significant imperfections due to greater welding heat input, which offset the advantage of their section moment of inertia and resulted in similar bearing capacities between T3 and T4 specimens. Under load welding affected the development direction of initial imperfections, and obvious deformation and axial force degradation occurred in the members after cooling. The finite element models showed high prediction accuracy, and this study can provide a basis for engineering applications.