Study on the global stability of members strengthened with outer sleeves

This paper presents a prefabricated outer-sleeve strengthening method to address buckling of compression members in space structures. Eleven axial compression specimens and accompanying numerical analyses investigate the influence of key parameters on global stability. Results show that sleeve reinforcement significantly increases the ultimate bearing capacity, and failure modes are dominated by buckling at the middle span and sleeve slippage. It is revealed that rational hoop spacing is critical for preventing capacity degradation, and an optimal configuration is identified to ensure effective composite action. Finite-element analyses indicate that increasing geometric dimensions such as sleeve thickness and outer diameter effectively enhances the capacity through increased moment of inertia. Furthermore, the sensitivity of the strengthened members to initial imperfections is quantified. Theoretical derivations demonstrate that the lateral restraint provided by the sleeve significantly reduces the equivalent slenderness ratio, confirming that lateral restraint governs stability improvement. Based on the small-deflection theory and static equilibrium conditions, the prediction formula for the ultimate capacity of sleeved reinforced members is derived. Verification results demonstrate good agreement between the theoretical predicted values and experimental values. The findings offer a theoretical basis for engineering practice. • An outer-sleeve method is proposed to prevent buckling. • Key parameters (spacing, dimensions, imperfection) are studied for capacity and failure modes. • Capacity formula is derived via small-deflection theory.