Compression performance of FRP-steel composite tube-confined ultrahigh-performance concrete (UHPC) columns

A new ultrahigh-performance concrete (UHPC)-filled fibre-reinforced polymer (FRP)-steel composite tube column (UHPCFSCT) was designed. This structure uses not only UHPC with high strength and durability to reduce the section size and improve the stiffness of the column but also FRP-steel composite tubes as confinement tubes to reduce the brittleness of the UHPC. Thirty-two UHPCFSCTs were subjected to monotonic axial compression tests. The key parameters include the number of FRP layers, FRP type, FRP hybrid condition and loading mode. The full-section-loaded specimens mainly exhibit shear failure, while the core-loaded specimens mainly exhibit middle expansion deformation. The stress-strain curves of UHPCFSCTs represent three types of columns with different numbers of FRP layers and FRP types: columns with weak, medium and strong confinements. The weak and medium confinement curves exhibit a softening section after the elastic-plastic stage, and the strong confinement curve shows a bilinear response. With the increase in the number of FRP layers, compared with those of the unconfined UHPC column, the ratios of the increases in peak stress, ultimate stress, and ultimate strain are 1.436-2.794, 2.046-4.822 and 0.778-2.315, respectively. The bearing capacity of the CFRP-confined specimens is stronger, while the deformation capacity of the BFRP-confined specimens is stronger. The ultimate stresses of the core-loaded specimens are 19.6%-30.6% higher than those of the full-section-loaded specimens. Existing strength models were used to evaluate the test data of UHPCFSCTs, and the Hu et al. model was used to predict the strength of UHPCFSCTs under core loading. Finally, through database regression analysis, a strength model that can be used to predict steel tube-confined UHPC, FRP-confined UHPC and UHPCFSCT strength under full-section loading was proposed.

Automated summary

A new type of ultrahigh-performance concrete-filled fibre-reinforced polymer-steel composite tube column was designed to reduce section size and improve column stiffness using high strength and durable UHPC, while also reducing brittleness by using FRP-steel composite tubes as confinement. The study analyzed key parameters through experimental tests and proposed strength prediction models.