柱失效方程中荷载相关特性对承载力抗震设计可靠度的影响

以竖向荷载和水平地震作用组合下的钢筋混凝土柱和钢柱为对象,研究了失效方程中荷载相关特性对柱承载力抗震可靠性的影响。根据现行《混凝土结构设计规范》和《钢结构设计规范》分析了不同柱弯矩轴力相关曲线的特性。结合多个框架结构实例,对比了柱失效方程中荷载相关曲线与规范考虑情形的异同。实例分析表明:水平地震和竖向荷载组合作用下,小偏压RC柱和工字型钢柱的荷载相关曲线与规范考虑的情形较为符合,均近似为负相关的直线;水平地震和竖向荷载组合作用下,大偏压RC柱的荷载相关曲线则与规范考虑的情形有较大出入,存在明显的正相关段部分。在此基础上,考虑失效方程复杂特性,依据已有的荷载和抗力变量概率模型,采用Monte Carlo法分析了水平地震和竖向荷载组合作用下柱的可靠性。结果表明:钢柱和小偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化幅度较小,与规范模式计算结果较接近;大偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化会有较大幅度波动,与规范模式计算结果差异较大;当轴压力荷载效应比值为负时,大偏压RC柱的承载力抗震可靠度会低于规范计算值较多,现行柱可靠性设计方法会偏于不安全。

Influence of correlations between loads in failure function on design reliability of seismic capacity for columns

The concrete and steel columns subj ected to a combination of vertical load and horizontal earthquake action are used to study the influence of correlations between loads in failure function on design reliability of seismic capacity of columns.According to the current Code for Design of Concrete Structures and Code for Design of Steel Structures,the correlations between moment and axial force are analyzed for different columns.Through comparisons of different columns in several frame structures, the similarities and differences are investigated between the load interaction curves and those considered in codes.It is indicated that the load interaction curves under this combination match well with those considered in codes for RC columns with compression failure and steel columns with I-shaped section, and they are all negatively correlated straight lines approximately;the load interaction curve of RC column with tension failure is largely different from that considered in codes,and obviously has some positive correlation parts. Based the complex failure function, reliability of columns under this combination is analyzed with the Monte Carlo method and current statistics of load and resistance.The results show that:(1 )the reliability indexes of seismic capacity vary lightly with different load effect ratios based on axial force for steel columns and RC columns with compression failure,and are close to those based on the codes;(2 )the reliability indexes vary greatly with different load effect ratios based on axial force for RC columns with tension failure,and are also largely different from those based on the codes;(3)the reliability indexes are lower than those based on the codes for RC columns with tension failure when the load effect ratio based on axial force is negative,as a consequence,the current reliability-based design method of columns may be unsafe in this case.