我国抗震规范时程分析中地震动的输入数量

Number of Earthquake Ground Motion Inputs for Time-History Analysis of Seismic Design Code in China

针对我国现行建筑抗震规范时程分析中地震动输入数量这一问题开展研究.首先基于结构响应参数服从对数正态分布的理论假设,通过500次/组蒙特卡罗抽样,模拟了两种不同输入地震动数量方案下的结构响应参数的累积概率分布曲线,表明了3条记录下选择响应最大值和七条记录下选择响应平均值两种输入方案的累积概率分布曲线存在较大差异:前者计算结果期望值要高于理论均值,且结果受响应离散性影响较大;后者计算结果的期望值就是响应理论均值本身,受响应离散性影响较小.同时对我国某10层平面RC框架进行弹塑性时程分析,结果表明:3条记录选取最大值的输入方案下结构响应预测均值要显著高于增加记录选取数量和控制记录间离散性的其他输入方案;建议在7条及以上强震动记录下的响应均值的基础上,以记录数量与响应离散性作为参数,通过经验修正公式来计算0.84分位值,以得到满足规范要求的84%以上保证率的计算结果,并对该经验修正公式在我国抗震规范下的适用性做了结构数值模拟验证.

This study aims to determine a proper input number of strong motion recordings for structural timehistory analysis in China seismic design code.The cumulative probability curves of structural response under different number of records were simulated using 500 times of Monte Carlo samplings based on the assumption that the seismic demand can be represented by a lognormal distribution.Consequently,significant difference was observed in cumulative probability curves between using the maximum response of three ground motions and using the average response of seven or more ground motions:in the former,the expectation of results is much higher than the theoretical mean structural response and is significantly affected by the structural response variation;while in the latter,the expectation of results is close to the theoretical mean structural response.In addition,nonlinear time-history analysis was carried out of a 10-story typical reinforced concrete(RC)frame according to Chinese seismic code.It turns out that using three records has a significantly higher mean MIDR(maximum inter-story displacement angle)and COV(coefficients of variation)compared with other schemes using more records as input and controlling the record-to-record variation.Finally,on the basis of the response mean values of seven or more strong vibration records,an empirical correction formula using record number and structural response variation as parameters was proposed to calculate the 0.84 quantile value to guarantee the assurance rate of 84%required by seismic design code.The applicability of the empirical correction formula under the seismic code of China is verified by numerical simulation of the 10-story RC frame.