高温下无粘结预应力混凝土扁梁试验研究

Experimental research on unbonded prestressed concrete flat beams under high temperature

通过自行研制开发的大型拼装式多功能电力加热炉,按照ISO834标准曲线升温,对26根无粘结预应力混凝土扁梁试件进行高温下试验研究。试验中观测了试件表面出现的渗水、油脂流淌与混凝土爆裂及外观颜色变化等宏观现象,研究了高温下试件变形、无粘结预应力筋的应力等力学性能的变化规律,分析了不同初始荷载、混凝土净保护层厚度及综合配筋指标等主要因素对其高温下力学性能的影响。试验结果表明:高温下试件发生动态连续变形,升温初期跨中挠度增加较小,温度较高时跨中挠度增长较大;预应力变化比较复杂;在同等升温条件下,试件承受的初始恒载越大,挠度变形也越大;增加混凝土保护层厚度,能延缓其内部钢筋的升温,提高试件的抗火性能;综合配筋指标q0较小的试件抵抗高温变形的能力较差。

In this research,26 unbonded prestressed concrete flat beams were tested under high temperature that was elevated gradually following the ISO 834 time-temperature standard curve using the large scale assembled electrical heating furnace self designed and manufactured.The macroscopical phenomena of water penetration,lube flowing,spalling of concrete and exterior color change were observed.The beam deformation in fire and the stress in debonded prestressing wires were investigated.The influences of initial load,concrete cover thickness and integrative steel ratio on the mechanical behavior of specimens under high temperature were studied.Test results indicate that the dynamic continuous deformation which increase small in the initial heating time but large later and the complicated varieties of prestressed tendons occurred at high temperature.The deflections are increased when supporting more initial loads.The elavating of steel rebars temperature is delayed and the fire-resistance behavior of members are improved when increasing the thickness of concrete cover.Capability of resisting deformation of the members with low integrative reinforcement ratio q0 is weak.