单层球面网壳考虑一致倒塌概率的倒塌安全储备分析

COLLAPSE SAFETY MARGIN ANALYSIS OF SINGLE-LAYER SPHERICAL LATTICE SHELLS CONSIDERING CONSISTENT COLLAPSE PROBABILITY

提出了考虑一致倒塌概率的单层球面网壳结构倒塌安全储备计算方法。以标准正态分布作为倒塌概率密度函数,采用指数型分布函数描述地震危险性,在假定网壳结构特大震倒塌率限值为10%的情况下,将两者积分得到了适用其50年内一致倒塌概率限值为0.46%,低于针对普通房屋建筑结构50年内一致倒塌概率1%的限值。在定义网壳结构特大地震强度水平的基础上,引入一致倒塌概率对其进行了修正。根据修正特大震强度,最终提出了针对网壳结构的倒塌安全储备系数(CMR)计算方法,这种做法可以使所做的抗倒塌设计更好地考虑到所有超越概率地震动水平,保证各抗震设防烈度下大跨网壳结构具备统一的倒塌概率限值要求。另外,通过谱形状参数对建议的倒塌安全储备计算结果进行了谱修正。针对三个算例网壳的增量动力分析对比了不同矢跨比和不同结构类型对倒塌安全储备以及50年倒塌概率的影响,三个算例结构均能满足倒塌概率限值的要求,50年倒塌概率与倒塌安全储备有较好的一致性。

A method is proposed to evaluate the collapse safety margin of single-layer lattice shells with the consideration of consistent collapse probability. With the assumed standard normal distribution for a collapse probability density function and the assumed exponential distribution for a seismic hazard function, the limit of 0.46% of 50-year consistent collapse probability for lattice shells is acquired through the integration of the two functions with a presumed collapse probability of 10% under major earthquakes. This limit is much lower than that suggested for ordinary building structures, i.e. 1%. The consistent collapse probability of large-span lattice shells is introduced to amend the pre-defined intensity of major earthquakes for large-span lattice shells. A new analytical method is proposed for the determination of the collapse margin ratio of lattice shells based on the amended intensity. The collapse resistance design combined with this method can account for earthquakeintensities with various probabilities of exceedance, making lattice shells have a unified limit of collapse probability with different seismic fortification intensities. Spectral correction is also carried out through spectral parameters in the final determination of collapse safety margin. The incremental dynamic analysis performed on three example single-layer spherical lattice shells is used to analyze the influence of a rise-span ratio and a structural system on collapse safety margin and 50-year collapse probability. All shells meet the requirement of the limit of 50-year consistent collapse probability. Consistency can be observed between collapse safety margin and 50-year collapse probability.