火灾后钢筋混凝土柱剩余承载力试验研究与数值分析

Experimental study and numerical analysis on residual bearing capacity of reinforced concrete columns after fire

为研究火灾作用后钢筋混凝土柱的剩余承载力,以受火时间(0、90和150min)、荷载偏心率(0、0.8和1.6)、柱长度(1224mm和2448mm)、截面类型(方形和圆形)以及截面尺寸(边长153mm和306mm)为试验参数,进行了15个标准火灾后钢筋混凝土柱力学性能的试验研究,获得了破坏形态、荷载-变形曲线、剩余承载力、应变和挠度特征。采用数值方法计算了火灾后钢筋混凝土柱的荷载-变形关系曲线,在参数分析基础上获得了火灾后钢筋混凝土柱剩余承载力设计方法。研究结果表明,经历90min高温后,截面边长306mm钢筋混凝土柱承载力损失率可比边长153mm柱减少16.5%,荷载偏心率超过0.8时的火灾后剩余承载力可比轴心受压情况降低60%以上。随着受火时间、荷载偏心率或长细比的增加,火灾后钢筋混凝土柱的承载力和刚度降低,受火90min和150min后承载力可分别下降52.0%~55.8%和61.1%~65.9%;随着截面尺寸、配筋率、荷载偏心率的增大或长细比的减小,火灾后承载力影响系数增加;提出的火灾后圆形、方矩形钢筋混凝土柱承载力影响系数简化计算公式与数值计算结果和试验结果吻合较好。

In order to study the residual bearing capacity of reinforced concrete columns after fire,15 reinforced concrete columns are tested after standard fire,using fire time(0,90 and 150min),load eccentricity(0,0.8 and 1.6),column height(1224 and 2448mm),section type(square and circular),and section size(153 and 306mm side width)as experimental parameters.The failure mode,load-deformation curve,residual bearing capacity,strain and deflection characteristics are obtained.Numerical method is used to calculate the load-deformation relationship curve of reinforced concrete columns after fire.Based on parametric analysis,a design method for residual bearing capacity of reinforced concrete columns after fire is obtained.The results indicate that after 9Omin fire exposure,the loss rate of bearing capacity of reinforced concrete columns with a section width of 306mm can be reduced by 16.5%compared to columns with a width of 153mm.The columns with the load eccentricity exceeding 0.8 exhibit more than 60%reduction in post-fire residual bearing capacity than the concentrically loaded columns.With the increase of fire time,load eccentricity or slenderness ratio,the bearing capacity and stiffness of reinforced concrete columns decrease after fire.After 90min and 150min of fire,the bearing capacity can decrease by 52.0~55.8%and 61.1~65.9%respectively.As the section size,reinforcement ratio,and load eccentricity increase or the slenderness ratio decreases,the influence coefficient of post fire bearing capacity increases.The proposed simplified calculation formula for the influence coefficient of bearing capacity of circular,square and rectangular reinforced concrete columns after exposure to fire is in good agreement with the numerical calculation results and experimental results.