大偏压RC柱中美两国规范抗震承载力设计方法对比与随机偏心距下的可靠度分析

Comparison of seismic capacity design methods in Chinese and American codes for RC columns with tension failure and its reliability analysis under random eccentricity

为研究大偏压RC柱不同抗震承载力设计方法的合理性,对比了中美两国规范中大偏压RC柱设计方法。考虑中国规范中对柱轴压比、配筋率等设计要求,得到了大偏压RC柱可靠度影响参数的合理组合情形,并明确了不同组合情形下两国规范方法承载力设计安全性的高低。基于中国规范中的承载力计算式,推导了以多个无量纲化设计参数表达的大偏压RC柱失效方程。考虑偏心距随机特性,分析了按两国规范方法设计的大偏压RC柱在不同设计参数下的抗震可靠度。结果表明:当中国规范方法中的柱端弯矩增大系数提高时,大偏压RC柱失效概率随其余参数变化的幅度亦随之增大;按美国规范方法计算的各种情形下的可靠指标平均值接近于按中国规范柱端弯矩增大系数1.5计算的可靠指标平均值;当两国规范方法对应的可靠指标平均值高于2.66时,大偏压RC柱失效概率会随各设计参数变化而出现高达数百倍差异的大幅度波动。

To explore the rationality of different design methods on seismic capacity of RC columns with tension failure,comparisons were made between the design methods in the Chinese and American codes. According to the design requirements in the Chinese code,e. g. axial compression ratio,reinforcement ratio,etc.,the rational combinations were obtained for parameters with strong effects on reliability,and the difference in the design safety of the two code-based methods was clarified. With the bearing capacity formulas in the Chinese code,the failure function was obtained and expressed by multiple normalized design parameters. Considering the random properties of eccentricity,the seismic capacity reliability with different design parameters was analyzed for RC columns with tension failure designed by these two code-based methods. The results indicate that: with the increase of the column moment amplification factor in the Chinese code,the variations of failure probabilities with other different parameters increase dramatically for RC columns with tension failure; the mean value of reliability indices in different cases based on the American code is close to that based on the Chinese code with a column moment amplification factor 1. 5; when the mean values of reliability indices are larger than 2. 66,the variations of failure probabilities in different cases are as much as hundreds of times for RC columns with tension failure designed by these two code-based methods.