Dominant failure modes in stochastic structural systems

In an analysis of redundant structural systems in which either or both loading systems and/or member resistances are stochastic variables, all modes of failure are potentially of significance in the calculation of structural reliability. In practice, however, many modes do not contribute very much, and a problem has been to identify those modes which are stochastically dominant.In this paper a general, iterative procedure called the Truncates Enumeration Method [TEM] to determine the most stochastically dominant modes is derived from successive systematic curtailment of the results which would be obtained by complete enumeration. In this way, it is shown that the procedure presented has the capability to produce all dominant modes to within the accuracy of the criteria used for curtailment. The method is similar to that proposed by Murotsu et al.It is also shown that the incremental load method (ILM), proposed by Moses et al., has certain features common to TEM, that both techniques are essentially incremental in nature and that both methods produced the same mode failure probability statement, each using quite distinct procedures. It is finally argued that the methods are not restricted merely to the materials behaviour properties studied thus far by their proponents.     

An approach to reliability-based optimization of redundant structures

This paper proposes an optimum design procedure for redundant structures with the constraints on the formation probabilities of structural failure modes. Although there exist numerous failure modes in a large-scale redundant structure, it is found that only a representative group consisting of some dominant failure modes needs to be considered in the optimization process. The proposed procedure introduces such dominant modes step by step from various design stages to keep the total number of the constraints at a minimum level. A branch-and-bound technique is used to identify dominant failure modes in a design state. Some analytical methods are discussed for the calculation of the formation probabilities of failure modes in the optimum design process. A numerical example is given to illustrate the effectiveness of the proposed procedure.     

风荷载作用下输电塔结构体系可靠度分析

用荷载增量法结合有限元分析技术,通过枚举列出输电塔体系的主要失效路径,提出了蒙特卡洛概率方法,并通过Matlab软件计算出各输电塔体系的失效概率,最后以一大型输电塔进行了可靠度计算。     

Sensitivity and importance measures in structural reliability

In multivariate reliability problems, which depend on one or more parameters τ, a sensitivity factor α_E[τ] is defined as the derivative of the equivalent reliability index β_E(τ)=?φ^?1[P _f (τ)] with P _f (τ) the failure probability. α_E[τ] expresses the change of α_E(τ) due to small variations of τ. Since the numerical evaluation of α_E[τ] is usually impractical, an approximation α_E[τ]≈α[τ] is derived, which is asymptotically exact for extreme reliability levels. Simple formulae for α[τ] are given. The approximation α_E[τ]:a[τ] also provides the basis for a better understanding of the commonly used alpha values α_i=?1/βu i? as importance measures for stochastic variables.     

An assessment of high-order bounds for structural reliability

Second-order bounds are often used to estimate the reliability of series structural systems. However, the quality of second-order bounds is poor when the failure modes are highly correlated. This paper examines the merit of third and higher-order bounds. First, the general form of the nth-order upper and lower bounds is derived. Second, an efficient algorithm for computing the n-dimensional multinormal integral is presented. Finally, the performance of the third and fourth-order bounds is examined in three numerical examples. These bounds can provide significant improvement over the second-order bounds, particularly when the number of significant failure modes is small (less than 20) or when the correlations between modes are somewhat localized.     

具有中介状态的工程系统的可靠性分析

提出了其单元具有"安全-中介-失效"工作模式的各种系统的可靠性分析方法.这时,系统及其单元均具有安全、中介、失效三种工作状态.可靠性分析的结果是求出系统的安全概率PR、中介概率PM和失效概率PF.它们联合起来构成可靠性向量[PR,PM,PF].在分析中还考虑了系统各单元间失效相关性问题.     

Generation of dominant modes and reliability analysis of frames

The paper presents a technique for reliability analysis of frames using the stiffness matrix method of linear elastic and piecewise linear elastic-plastic structural analysis and the first order second moment reliability method. It involves automatic generation of stochastically dominant mechanisms (modes) and their safety margin equations and calculation of bounds on the system reliability. Based on the computational experiments, logical strategies are proposed for selection of plastic hinges and branching of failure paths to identify stochastically dominant mechanisms. The proposed method is illustrated with numerical examples. The results show very good agreement with the results of other research workers. The proposed method of generating stochastically dominant modes is simple and fairly efficient and less computer-time consuming.     

Reliability analysis of frame structures with brittle components

A review is provided of the recent developments in the reliability analysis of ductile (elastic-plastic) systems and of the stable configuration approach of structural system reliability analysis. These are combined to obtain a methodology for evaluating the reliability of frames that have primarily ductile components but also a few brittle components. The methodology is applied to two frame structures.     

中国钢结构设计的安全性评定

论述钢结构设计中的安全性评定研究方法及可推荐的标准．着重讨论了钢结构工程中安全系统工程、可靠性分析、可靠度评估的设计新概念，并提出了评定钢结构系统可靠性的方法及使用寿命的评估．     

结构全寿命的耐久性与安全性、适用性的关系

在结构可靠度分析和设计中,尚未考虑耐久性对结构安全性和适用性的影响,缺乏相应的耐久性失效准则,对耐久性概念的认识还存在一定的分歧,针对上述存在的问题,从结构全寿命的角度出发,分析了安全性、适用性和耐久性三者的基本概念,明确了三者的基本内涵。通过分析影响结构抗力变化的各种因素,结构性能随时间变化的过程,指出在结构全寿命期内,不同的耐久性水平对结构安全性和适用性将产生不同的影响,三者之间是相互制约、相互影响的交叉关系,重新定义了结构的耐久性。提出了基于性能设计的耐久性极限状态设计新理念,同时指出性能极限状态设计可根据不同的耐久性要求,定义不同的耐久性极限状态,对同一结构构件,若采用不同的性能极限状态,结构的失效概率或使用寿命会有较大的差别。     

建筑结构可靠性理论应用与发展

介绍了建筑结构可靠性的概念及分析步骤,阐述了目前识别结构体系主要失效模式的理论和算法,并对结构体系的分类以及失效概率计算方法作了具体说明,对促进结构体系可靠性理论研究具有积极的指导意义。     

结构可靠度计算方法综述

围绕建筑结构的可靠度计算,对寻求结构的主要失效模式及失效模式间的相关问题进行了阐述,总结了近年来国内外计算结构可靠度的各种方法,并对这些方法的优缺点进行了分析比较,为实际建筑结构的可靠度分析提供了参考。     

现役工业厂房钢筋混凝土连续板的可靠度计算

钢筋混凝土连续板经过一段时间的使用 ,其抗力和荷载效应都与设计时的不同。采用串联分析模型 ,计算结构体系的失效概率。即结构体系中有一个构件失效 ,则整个结构体系失效。连续板的失效概率应为荷载出现概率和相应荷载作用下的失效概率乘积的总和。以此对结构的安全性进行评估 ,为厂房的维修决策提供依据     

浅谈结构可靠度研究

阐述了结构可靠度的概念、基本理论,从结构工程角度分析其影响因素,并介绍了可靠度研究发展趋势,提出对目前可靠度设计的几点认识,以指导实践,确保结构稳定、安全。     

超高压输电杆塔结构体系可靠性研究

应用载荷增量最小准则法识别超高压输电杆塔结构体系的主要失效模式,同时结合blatlab优化工具箱。编制可靠度计算程序,工程算例计算结果表明现行超高压输电杆塔结构体系可靠度指标偏低,应适当提高。     

型钢混凝土结构构造设计优化与建议

对型钢混凝土构造设计提出优化方案,指出优化设计应充分考虑柱—梁节点受力性能和方便施工;分析了全型钢混凝土框架体系的优越性;提出确定型钢混凝土构件合理含钢率的原则,以指导类似工程的设计。     

深基坑边坡土钉支护稳定性的可靠度分析

对土坡分析中较为经典的圆弧滑动法进行改进,使其可以同时考虑土钉的拔出破坏和强度破坏两种破坏形式。鉴于传统确定性方法的局限性,综合考虑了土钉与土体之间的界面摩阻力强度值,以及土体强度参数的不确定性,经过对各参数及参数间关系的处理,对土钉支护结构的内部稳定进行了可靠度分析,推导出可靠度的计算公式,最后通过具体实例验证了该法,为土钉支护的设计由传统的安全系数法向更为经济、科学的分项安全系数法转变提供参考和依据。     

Probability-based criteria for structural design

Probability-based loading and resistance criteria are presented that are suitable for routine safety checking in design. The criteria are based on a comprehensive analysis of statistical data on structural loads and resistances and an examination of levels of reliability implied by the use of current design standards and specifications. The criteria are intended to be used in specifications that are oriented towards limit states design.