高强箍筋约束超高性能混凝土柱轴压性能

通过5根高强箍筋约束超高性能混凝土(Ultra high performance concrete，UHPC)柱及4根普通箍筋约束UHPC柱的轴心受压试验，对其承载力、破坏形态、钢筋应变及应力-应变曲线进行了研究，并结合延性、韧性指数分析了体积配箍率、箍筋强度、箍筋间距及形式对约束UHPC轴压性能的影响。结果表明:所有约束柱均表现为延性破坏，高强箍筋可减轻约束UHPC的破坏程度；高体积率、小间距、形式复杂的高强箍筋约束UHPC，约束效率高，承载力及变形能力提高显著，轴压性能较理想；体积配箍率对轴压性能的影响程度大于箍筋强度；影响体积配箍率变化的因素中，箍筋间距对改善约束性能的贡献最大，依次是箍筋形式和直径；高强箍筋可有效约束UHPC，在提高约束UHPC强度、变形性能及残余承载力方面明显优于普通箍筋；纵筋微曲会加速保护层剥离，密配高强箍筋能有效延迟纵筋屈曲，显著提高约束性能；纵筋微曲会削弱高强箍筋对核心UHPC的约束效果，建议采用高强纵筋与高强箍筋组合。在试验的基础上给出了能较准确预测箍筋约束UHPC柱承载力的计算式。 

Axial compression behavior of ultra-high performance concrete columns confined by high-strength stirrups

Based on the axial compression test of 5 ultra-high performance concrete (UHPC) columns confined by high-strength stirrups and 4 UHPC columns confined by normal-strength stirrups, the bearing capacity, failure mode, steel strain and stress-strain curve for the confined UHPC columns were studied, and the influences of volume stirrup ratio, strength, spacing and configuration of stirrup on the axial compression behavior of confined UHPC were analyzed by combining ductility and toughness index. The results show that all the specimens have ductility damages, and the damage degree of UHPC columns confined by high-strength stirrups is lighter. The confined UHPC columns with high volume stirrup ratio, closely spaced, high-strength and complex ties configuration have good confinement efficiency, bearing capacity and deformation performance, which also leads to an ideal axial compression behavior. The effect of volume stirrup ratio on the axial compression behavior of specimens is greater than that of stirrup strength. Among the three factors affecting the volume stirrup ratio, such as spacing, configuration and diameter of stirrup, the stirrup spacing contributes most to the improvement of confinement performance, followed by the configuration and diameter of stirrup. The UHPC confined by high-strength stirrups presents better axial compression performance and residual bearing capacity than the normal-stirrups. The micro-bending of the longitudinal bars accelerates the cover spalling, while the high-strength stirrups with close space effectively delays the buckling of longitudinal bars, and significantly improves the overall performance of the confined UHPC. The micro-bending of longitudinal bars weakens the confine effect of the high-strength stirrups on the core UHPC, and the combination of high-strength longitudinal bars and stirrups is suggested. Based on the test data, the formulas to determine the bearing capacity of UHPC columns confined by stirrups are drawn.