超高强混凝土型钢组合柱抗火性能试验研究

Experimental study on fire resistance of ultra-high strength concrete encased steel columns

为研究型钢保护层厚度、柱截面尺寸、荷载比、长细比和箍筋间距对超高强混凝土型钢组合柱高温承载力的影响,开展了14根纤维增强120 MPa混凝土型钢组合柱在ISO 834标准升温曲线下的承载力试验。组合柱高温破坏现象和竖向位移历程表明:体积掺量0.15%的聚丙烯纤维能够有效防止超高强混凝土的高温爆裂;随着长细比的增加,组合柱从截面强度破坏转变为屈曲破坏。总体上,竖向位移历程曲线可分为受火初期膨胀阶段、后继的压缩变形稳定增长阶段和破坏前的压缩变形急剧增长阶段。纤维增强120 MPa混凝土型钢组合柱的耐火极限随着长细比和荷载比的增加而降低;随着截面尺寸和型钢保护层的增加而增长;双肢箍间距在80~150 mm范围变化,对耐火极限的影响较小。对比耐火极限的试验值和EN 1994-1-2及规程DBJ/T 15-81—2011简化计算方法的建议值发现,EN 1994-1-2的计算值低于试验值30%~186%,规程DBJ/T 15-81—2011的计算值与试验值偏差为-49%~16%。因此,现行规范不适用于预测120 MPa混凝土型钢组合柱的耐火极限。

Fourteen fiber reinforced ultra-high strength concrete encased steel columns exposed to ISO 834 standard fire were tested under axial compression in this study. The influences of thickness of concrete cover, cross-section size, load ratio, slenderness ratio and hoop spacing on the bearing capacity of the column at the elevated temperature were studied. The failure modes and the vertical displacement-time history curves of the specimens show that the use of 0.15% polypropylene(PP) fiber by volume can prevent the spalling of the ultra-high strength concrete effectively. With the increase of slenderness ratio, the cross-sectional strength failure changes to buckling failure. In general, the vertical displacement-time history curves consist of three phases: thermal expansion, gradually compressive shortening and rapid development of deflection before failure. With the increase of slenderness ratio and load ratio, the fire resistance decreases. With the increase of cross-sectional size and thickness of concrete cover, the fire resistance increases. The varying of the hoop spacing from 80 mm to 150 mm has little influence on the fire resistance. Compared with the measured fire resistance, the fire resistances evaluated by EN 1994-1-2 are lower by 30% to 186%. The deviation between the fire resistance evaluated by DBJ/T 15-81—2011 and the measured value ranges from-49% to 16%. This indicates that the existing codes are not suitable for the fire resistance design of 120 MPa fiber reinforced ultra-high strength concrete encased steel columns at elevated temperatures and need to be modified.