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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。
Bottom frame structure because of its own characteristics of poor fire resistance, collapse may occur in the fire. In order to correctly evaluate the fire resistance of this kind of structure, six building fire tests were carried out using wood as fuel. The results show that: (1) Compared with the RC frame, the bottom frame has poor fire resistance. When there is more combustible material in the lower commercial building, the possibility of human collapsing when the fire fails is greater. ② The thermal expansion and deformation of reinforced concrete members in the fire are large, and the post-strength of concrete has a great influence on the fire resistance. To evaluate or predict the fire resistance of such structures, the temperature internal force and the post-concrete strength must be considered. ③ Concrete age more than a year and a half, the cube strength does not exceed 50MPa, the fire will not occur in general burst. ④ vertical deformation of buildings and cracks in the center pillar can be used as a precursor to the failure of the center pillar: After the fire has been ignited for more than 60m in, when the vertical deformation of the building reaches a compression average value of 2mm within 10m in; when the concrete body surrounded by fire columns Vertical cracks occur in the middle of the width (or height) of the cross section, especially when longer or wider cracks are formed or when dense cracks occur somewhere. Recommendation: When the lower part of the commercial fire load larger room, increase the cross-sectional size of the way to reduce the axial compression ratio.