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阐述基于可靠度理论的基础设计的评估。首先总结具有结构抗力和荷载效应2个基础变量的结构可靠度基本理论。结构抗力的不确定性可以由统计学上的平均值和变异系数(cov或)Ω来描述。变异系数指变量的标准差和平均值的比值。敏感度分析的结果显示结构抗力的变异系数(ΩR)在其应用范围之内时,在分析结构可靠度方面扮演着相当重要的角色。基于这些阐述,在预先指定的风险水平(pf)上ΩR一定有其上限。当结构抗力呈正态分布的时候,这个极限ΩR独立于荷载效应随机性,和安全指数β成反比。安全指数可以定义为在标准正态分布区间极限状态到原点之间的最小距离。在这个极限ΩR之下,结构可以在预定风险水平之下安全工作。中心安全系数(FS)可以由结构抗力和荷载效应的变异系数根据平方关系求得。然而,一些情况下结构抗力为非正态分布的情况并不少见。因此,等效正态分布的概念可以用来得到非正态分布结构抗力的ΩR极限。地质方面的随机变量可能是正态分布,也可能是非正态分布,结构抗力中基本变量之间的关系可能是线性也可能是非线性,或者非常复杂以致于结构抗力只能通过有限元分析才能得到。在此情况下,随机数可以通过蒙特卡洛模拟技术获得。拟合的结构抗力的分布可以在随机试验的基础上通过配合度检验确定。现实中,土壤的力学特性不是各向同性的,同样也不能认为是单一材料的,它们的不确定性是不可以被忽略的。简便的设计方式认为不确定参数是常数,并且通过使用定值的安全系数来确定结构截面,设计原则没有将土壤参数对安全系数的影响考虑进去。参考计算出来的失效概率表明,确定值的安全系数法无法保证足够的安全。因此,在某种情况下,安全系数大于等于3,对于结构容许承受能力,并不能认为太保守。
Describe the evaluation of basic design based on reliability theory. Firstly, the basic theory of structural reliability with two basic variables of structural resistance and load effect is summarized. The structural resistance uncertainty can be described by the statistical mean and coefficient of variation (cov or) Ω. Coefficient of variation refers to the standard deviation of the variable and the average ratio. Sensitivity analysis results show that the coefficient of variation (ΩR) of structural resistance within its scope of application plays an important role in the analysis of structural reliability. Based on these statements, ΩR must have its upper limit at a pre-specified risk level (pf). When the structural resistance is normally distributed, this limit ΩR is independent of the randomness of the loading effect and inversely proportional to the safety index β. The safety index can be defined as the minimum distance to the origin between the limit state of the standard normal distribution interval. Under this limit ΩR, the structure can safely operate below a predetermined level of risk. The center safety factor (FS) can be obtained from the square relationship by the coefficient of variation of structural resistance and load effect. However, in some cases it is not uncommon for structural resistance to be non-normal. Therefore, the concept of equivalent normal distribution can be used to obtain the ΩR limit of structurally non-normal distribution. Geological random variables may be normal distribution or non-normal distribution. The relationship between basic variables in structural resistance may be linear or non-linear, or so complex that structural resistance can only be obtained by finite element analysis . In this case, the random number can be obtained by Monte Carlo simulation. The distribution of the fitted structural resistance can be determined on the basis of a randomized test by the fit test. In fact, the mechanical properties of soils are not isotropic, nor can they be considered as a single material, and their uncertainties can not be ignored. The simple design approach assumes that the uncertain parameters are constants, and that the structural cross-section is determined by using the set safety factor, the design principle does not take into account the effect of soil parameters on the safety factor. The calculated failure probability shows that the safety factor method of determining the value can not guarantee sufficient safety. Therefore, in some cases, the safety factor is greater than or equal to 3, which is not considered too conservative for the structure to tolerate.