足尺平板无梁楼盖抗火性能试验研究

Experimental study on fire resistance properties of full-scale flat-plate floor subjected to fire

对2个足尺钢筋混凝土平板无梁楼盖试件进行了抗火试验,测量了火灾作用下板的平面内(水平)位移和平面外(竖向)位移等,考察了板的约束反力变化,分析了混凝土板沿厚度的温度分布以及钢筋的温度变化。结果表明:单面受火的钢筋混凝土板沿厚度的温度呈非线性分布,温度梯度随时间的增长而快速增大,并且毛细孔水和凝胶水等水分的存在使混凝土在100℃时产生了升温水平段;水分不仅影响了混凝土的升温,还使受火混凝土产生爆裂,含水率太高时板将因混凝土的爆裂而导致破坏;柱上板带和跨中板带的约束反力均产生了显著变化,柱上板带的约束反力由第4 min时的8.2 kN/m下降到试验结束时的2.7 kN/m,跨中板带则由第4 min时的4.5 kN/m下降到接近0;平板无梁楼盖的板顶裂缝最终形成对角呈双曲线形,与传统塑性铰线理论的柱附近局部屈服线模式一致。

Two full-scale reinforced concrete fiat-plate floors were tested in fire. The horizontal and vertical deflections of the slab edges under fire were measured. The variation of restraining force was observed. The temperature distribution of concrete and temperature variation of rebars were analyzed. The results indicate that the temperature distribution along depth of the slab with single surface being exposed to fire is nonlinear and the temperature variation increases quickly with time. There is a plateau in the temperature rise at 100 ~C level attributed to the existence of capillary water and gel water. The moisture also leads to spalling of concrete, which might lead to slab destruction if the water content is too high. Significant variation of the restraining force occurs both in column strips and middle strips of the fiat-plate floor. The restraining force in column strips decrease from 8.2 kN/m at four minute after ignition to 2.7 kN/m at the end of test. And the restraining force in middle strips decrease from 4.5 kN/m at four minute after ignition to nearly 0 at the end of test. The top surface cracks form in a hyperbolic pattern between every diagonal columns of the fiat-plate floor, consistent with local buckling nearby columns of the classical yield line theory.