混凝土轴压方柱满足目标抗火可靠指标的建议截面

对混凝土轴压柱抗火计算所用荷载比与其常温设计荷载比的换算关系进行了推导和分析,分别针对耐火等级一级和二级情况下的柱耐火极限要求,给出了四面受火轴压方柱满足目标抗火可靠指标的最小截面取值。研究表明:①常温设计荷载比大致为抗火计算所用荷载比的2～5倍,一般混凝土柱可近似取2.5倍;②荷载比小于0.2时,现行规范给出的300mm×300mm截面柱,在抗火可靠指标不小于目标抗火可靠指标的情况下可以满足二级耐火要求;③荷载比和耐火等级是影响轴压柱最小截面取值的主要因素。

Suggested Sections for Axially Loaded Concrete Columns in Meeting the Target Fire-resistance Reliability Index

A conversion relationship between the load ratio used in fire-resistance calculation and that used in structural design at normal temperature is analyzed for axially loaded concrete columns.To meet the target fire-resistance reliability indexes for fire endurances related to Grade 1 and Grade 2 fire resistance ratings,respectively,the minimum sectional dimensions for four-face heated axially loaded concrete columns are proposed.The results show that:(a) the design load ratio at room temperature is about 2~5 times of that for fire-resistance calculation,and an approximate value of 2.5 is feasible to common concrete columns;(b) in the case that the load ratio is less than 0.2 and the fire-resistance reliability index is not less than the target index,columns with a section of 300 mm×300 mm given in current code can meet the Grade 2 fire resistance requirement;and(c) load ratio and fire resistance rating are main factors that influence the minimum sectional dimensions of axially loaded concrete columns.