钢筋混凝土底框架结构框架中柱耐火性能试验研究

Experimental study on fire resistance of interior column in bottom RC frame

底框架结构因其自身特点耐火性较差,可能在火灾中发生倒塌。为正确评估该类结构的耐火性能,以木方为燃料进行6栋建筑火灾试验。结果表明:①与钢筋混凝土全框架相比,底框架结构耐火性差,当下部商业用房存在较多可燃物,人为干预火灾失效时倒塌可能性较大。②钢筋混凝土构件在火灾中的热膨胀变形较大,混凝土的后期强度对耐火性能影响也很大,评估或预测该类结构的耐火性能时必须考虑温度内力和混凝土的后期强度。③混凝土龄期在1年半以上,立方体强度不超过50MPa时,火灾中一般不会发生爆裂。④建筑物竖向变形和中柱裂缝可作为中柱失效的预兆:在火灾轰燃后60m in以上,当建筑物竖向变形在10m in内压缩均值达到2mm;当四面受火柱的混凝土本体在其截面宽度(或高度)中间部位发生竖向裂缝,尤其是形成较长或较宽裂缝,或某处出现较密集裂缝时。建议:当下部商用房间火灾荷载较大时,采用增大截面尺寸的方式适当降低轴压比。

Because of its characteristics,Bottom RC frame is poor in fire resistance,and,may collapse when in fire.In order to evaluate the fire resistance capability of this type of structure correctly,fire tests were carried out separately in six buildings,using wood as fuel.The results show that：（1） Bottom RC frame is worse than the RC frame in fire resistance.The building is more likely to collapse,when much more fuel is deposited in the first floor of the building and human intervention fire failed.（2） RC structures have large thermal expansion deformation in fire.The post-strength of concrete can significantly influence its capability of fire resistance.Thus,thermal internal forces and post-strength of concrete must be considered,when evaluating and forecasting the fire resistance capability of such buildings.（3）The burst of concrete would not appear when the concrete age is more than 18 months and the cubic strength is less than 50MPa.（4）Vertical deformation of the building and cracks in the column,whose all sides are exposed to fire,can be taken as the sign of collapse： 60 minutes later after flashover,when the average compression vertical deformation of building reached 2mm within 10 minutes;when vertical crack appeared in the middle cross-section width（or height） of element,especially when the cracks are longer or wider,or when dense cracks appeared somewhere else.The suggestion is that when fire load is large in the commercial room of the lower part of bottom RC frame buildings,the section size of the column should be increased to reduce the axial compression ratio appropriately.