Development and structural application of a compression-dominant FRP-to-metal sleeve joint for lattice columns

For structural systems such as fibre-reinforced polymer (FRP) lattice columns, where compression is the dominant load, an excessive focus on balancing tensile and compressive performance at the connections often leads to structural redundancy and reduced efficiency. This paper proposes a compression-dominant bolted sleeve joint with end-contact (BSJE), in which load transfer is achieved through the direct compression of the FRP sleeve's end face, combined with the shear resistance of the bolts. Results from axial compression tests on the joints indicate that the load-bearing efficiency of the BSJE connection is significantly improved. The average ultimate load‑bearing capacity of the BSJE specimens was 1.86 times that of the bonded-bolted sleeve joint (BBSJ) specimens and 4.34 times that of the bolted sleeve joint (BSJ) specimens. The GFRP tube cross‑section achieved a compressive strength utilisation rate of 89.6%. Building on these findings, experimental studies were conducted at two levels—isolated joints and two-leg lattice column assemblies—to systematically investigate the mechanical performance and failure mechanisms of the BSJE under pure axial compression and combined compression–flexure interaction. Based on the experimental and numerical analysis results, a load capacity envelope curve for the axial force–bending moment (P–M) relationship of the BSJE joint was established. The study indicates that the BSJE connection exhibits excellent load-carrying efficiency under pure axial compression. However, in the design of lattice columns, the reduction in capacity caused by the coupled compression–bending effect must be taken into account.