Research on the Ultimate Bearing Capacity of BFRP-Confined Square Steel Tubular Mortar Specimens Under Axial Compression

In order to study the mechanical properties of basalt fiber reinforced polymer （BFRP）-confined square steel tubular mortar specimens under axial compression， static axial compression tests were conducted on nine specimens with different BFRP layers and section heights. The characteristics of the load-square steel tube longitudinal strain （displacement） curve， failure mode， ultimate bearing capacity， and synergistic reaction between the square steel tube and BFRP were analyzed. ABAQUS simulations were used to obtain the nominal compressive stress-square steel tube longitudinal strain curves and deformation modes of the specimens. The effects of BFRP layers， square steel tube cross-sectional height， and other factors on the static performance of the specimens were investigated and discussed. Additionally， the effects of the number of BFRP layers and the height of the square steel tube section on the static performance of the specimens were explored. Based on performance analysis， the axial compressive strength （<italic>f</italic>_bfscy） of BFRP-confined square steel tubular mortar specimens was defined and fitted to obtain the formula for calculating their ultimate bearing capacity under axial compression. Applying this formula to optimize the ultimate bearing capacity of reinforced components in tunnel lining engineering， using the commonly-used Ι16 I-beam as the benchmark for replacement， and considering economic efficiency and space occupancy， this paper propose optimized parameters for reinforced components （<italic>w</italic>=54.2 mm、<italic>m</italic>=3、<italic>f</italic>_y=235 MPa、<italic>f</italic>_cu=80 MPa、<italic>f</italic>_bf=3092 MPa）.