基于弯矩和轴力随机相关特性的RC偏压构件可靠度分析

Reliability analysis based on random correlative characteristics between moment and axial force for RC member subjected to eccentric compression

我国现行规范在分析混凝土偏心受压构件可靠度时,未考虑轴力和弯矩的随机相关特性。基于此,首先推导了弯矩和轴力间相关系数与对应荷载效应比值的函数表达式,得到了相关系数随荷载效应比值变化的规律。在此基础上定性分析了弯矩和轴力的随机相关特性对大偏压和小偏压两类构件失效概率的不同影响规律。采用Monte Carlo方法计算了当水平荷载起控制作用时偏压构件在不同荷载效应比值下的可靠度。计算结果表明:按小偏压构件设计的可靠指标较为稳定,弯矩和轴力的相关性变化对其影响较小;而按大偏压构件设计的可靠指标较不稳定,弯矩和轴力的相关性变化对其影响较大。对典型框架柱的荷载效应比值进行了特性分析,指出框架柱的弯矩荷载效应比值一般是轴力荷载效应比值的数倍,导致按大偏压框架柱设计的可靠指标较低。最后分别对承受水平风荷载和地震作用的框架结构中的大偏压柱进行了可靠度分析,分析结果表明大偏压框架柱可靠性较低。

The current code lacks considerations on the random correlative characteristics between moment and axial force in the reliability analysis of RC members subjected to eccentric compression.First,the function expression was derived between random correlative factors and corresponding load effect ratios.The varying rule was also obtained.Based on this analysis,the influences of different random correlation between moment and axial force on failure probability were qualitatively analyzed for the RC compressive members designed with large or small eccentricity.Then,the reliability was calculated with the Monte Carlo method for these two kinds of members under different load effect ratios when horizontal load dominated load combination.It shows that the reliability indices of the members designed with small eccentricity are stable and vary slightly under different random correlation between moment and axial force,while the reliability indices of the members designed with large eccentricity are unstable and vary greatly under different random correlation between moment and axial force.The characteristics of the load effect ratios were also discussed for the typical frame columns.It indicates that the load effect ratio of moment is several times bigger than that of axia force,resulting in low reliability indices for frame columns designed with large eccentricity.Finally,the reliability was analyzed for the columns designed with large eccentricity in practical frame structures under wind and earthquake action.The results validate that the reliability indices are low for frame columns designed with large eccentricity.