Axial compression performance of GFRP-confined hybrid fiber-reinforced UHPC columns

In order to further improve the mechanical properties of ultra-high-performance concrete (UHPC) columns confined with glass fiber-reinforced polymer (GFRP), a new strategy of reinforcing UHPC with a steel–polypropylene (PP) hybrid fiber was proposed. Subsequently, the effects of GFRP tube wall thickness and steel–PP fiber content on the axial compression performance of such columns were systematically studied. The results indicate that GFRP tube confinement can effectively mitigate the brittle failure tendency of UHPC columns, thus improving their deformation capacity prior to failure. When this confinement effect is synergistically coupled with the bridging action of hybrid fibers, the load-bearing capacity of the test specimens is significantly enhanced. On the basis of orthogonal test results, a combination of high-level confinement (using a 9 mm-thick GFRP tube) and moderate fiber content (incorporating 1.5% steel fibers and 0.1% PP fibers) is recommended for achieving optimal axial compression performance of the columns. Furthermore, through theoretical analysis, a calculation formula for the bearing capacity of GFRP-confined hybrid fiber-reinforced UHPC columns was established, and the results derived from this formula show a good correlation with the experimental data.