考虑轴向约束的钢筋混凝土梁高温下竖向推覆试验

Vertical Push-down Tests of RC Beams at High Temperature Considering Axial Restraint

为研究轴向约束对钢筋混凝土梁高温下大变形力学性能的影响,进行了1根常温和2根高温下约束梁的竖向推覆试验。比较分析了不同升温时间对轴向约束钢筋混凝土梁测点温度、升温反应及延性和耗能等的影响;重点研究了轴向约束钢筋混凝土梁的高温反应、破坏形态、承载能力和受力机制。结果表明:升温过程中,随着温度的升高,轴向约束钢筋混凝土梁不断向下挠曲,但炉温超过800℃之后,挠度有所恢复;由于受热膨胀引起的轴压力影响,高温下约束梁塑性铰区域明显缩小,其延性和耗能能力随着温度的升高而降低;高温作用产生的初始轴压力提高了梁的峰值承载力,但随着升温时间的延长,其提高幅度低于材料劣化对梁峰值承载力的降低幅度;初始轴压力使得高温梁在破坏前始终处于压弯机制;研究结果可为验证和校正火灾下约束混凝土梁力学行为的数值模拟以及理论分析提供可靠的试验数据,并为进一步探讨高温下钢筋混凝土约束梁大变形时的破坏准则提供依据。

In order to investigate the influence of axial restraint on the mechanical behaviours of fire-exposed reinforced concrete(RC) beams at large deformation, the push-down tests of one restrained beam at ambient temperature and two restrained beams at high temperature were carried out. The effects of different heating time on the measuring point temperature, heating response, ductility and energy dissipation of axially restrained RC beams were compared and analyzed. The thermal response, failure mode, bearing capacity and force mechanism of axially restrained RC beams were mainly studied. The results show that during the heating process, with the increase of temperature, the axially restrained RC beams deflect downward continuously, but the deflection recovers after the furnace temperature exceeds 800 ℃. Due to the influence of axial compression caused by thermal expansion, the plastic hinge area of restrained beams at high temperature is obviously reduced, and its ductility and energy dissipation capacity decrease with the increase of temperature. The initial axial compression caused by high temperature increases the peak bearing capacity of beams, but with the increase of heating time, the increase amplitude is less than the decrease amplitude of peak bearing capacity of beams caused by material deterioration. The initial axial compression makes high temperature beams always in bending mechanism before failure. The paper can provide reliable experimental data for verifying and modifying the numerical simulation as well as theoretical analysis of the mechanical behavior of confined concrete beams under fire, and provide a basis for further exploring the failure criteria of axially restrained RC beams under large deformation at high temperature.