钢筋混凝土框架结构基于可靠度的最可能倒塌失效模式分析

在建筑结构的抗震设计中,常常希望通过合理的设计,使结构能按预期的强柱弱梁失效模式破坏,通常通过提高柱端弯矩增大系数(COF)使结构满足“强柱弱梁”的要求。该文考虑上层、下层、中间层这3 类层间失效模式,采用结构可靠度理论,对钢筋混凝土框架结构最可能倒塌失效模式及完全梁铰式失效模式的相对发生概率进行研究。算例结果表明:当COF 较小时,结构最可能失效模式为中层失效模式;当COF 较大时,则结构倒塌由上层失效模式控制。研究结果可为罕遇或特大地震作用下结构的抗倒塌设计提供参考。     

计算结构可靠度指标的修正迭代算法

针对一次二阶矩法可靠度指标分析中验算点的计算问题,提出一种新的修正迭代算法。基于对文献已有迭代算法无法收敛原因的认识和讨论,提出一个迭代迂回振荡的判据,并在检测到迭代迂回振荡后,在经典的HL-RF迭代算法的基础上采用插值技术引入验算点的校正解。数值算例表明:该修正迭代算法一定程度上克服了迭代过程迂回振荡的问题,与经典的HL-RF算法以及文献已有算法相比,在迭代的收敛性和稳定性方面具有优势。     

基于修正混沌控制的一次二阶矩可靠度算法

在结构可靠度指标的求解中,HL-RF迭代算法由于其格式简单,效率高被广泛应用到一次二阶矩计算中。然而该方法仅适用于功能函数非线性程度低的情况,当功能函数非线性程度较高时,HL-RF算法常会出现混沌、振荡和周期解的现象,甚至导致不收敛。该文在混沌控制理论的基础上提出了一种新的修正的混沌控制算法来控制迭代过程中产生的振荡。该方法在保留基于混沌控制方法稳健性的同时提高了计算效率,并对迭代过程中振荡现象引入了一种新的判据。当迭代过程逐渐收敛到最可能失效点时,采用经典的HL-RF算法;当检测到振荡时,采用基于修正混沌控制的迭代算法。算例结果表明：基于修正混沌控制的迭代算法能有效解决迭代中的振荡问题,与经典的HL-RF算法相比,该算法具备效率和稳健性方面的优势。     

结构体系可靠度分析的失效模式识别方法

本文分别对极限状态体系和网络评估体系这两大类体系失效模式的判别方法进行简单地介绍,对每一种判别方法的特点进行总结,并对该领域的研究成果进行了比较系统的分类和阐述。     

结构体系可靠度分析中的最小方差抽样

本文研究了并联结构体系可靠度分析中以失效概率估计值方差最小为条件的重要抽样问题。由于直接对抽样样本平均值和标准差进行优选比较困难,因而本文首先建立了三个定理,据此并通过数例分析给出正态抽样样本平均值和标准差的建议取值范围。分析和实际模拟表明,在以正态分布进行抽样的前提下,合理选取抽样样本平均值和标准差,可使抽样效率进一步提高。     

一种高效的结构可靠度近似分析方法

本文简要讨论了结构的可靠度计算的数值模拟方法,如Monte-Carlo法、响应面和两点近似法;结合结构分析的确定性有限元法及可靠度计算的一次二阶矩法,提出了一种结构可靠度分析的近似方法;算例表明,当荷载的不确定性远大于结构的不确定性时,本文提出的方法满足工程精度要求,从而大大简化了结构可靠度分析过程。     

地基承载力可靠度指标不同计算方法的比较

本文分别采用改进的JC法、随机投点法以及改进的搜索适应重要抽样法来计算地基承载力可靠度指标,并在计算过程中考虑了土性指标的自相关性和互相关性,将这三种计算方法进行了比较,结果表明,重要抽样法具有更大的优越性。     

无失效数据情形可靠度的多层Bayes估计

对无失效数据的研究,是近些年来遇到的一个新的实际问题,对二项分布无失效数据,在可靠度的先验分布为 Ｂｅｔａ 分布 Ｂｅｔａ（ ０,１;１,ｂ） 和不完全 Ｂｅｔａ 分布 Ｂｅｔａ（ Ｒ Ｌ,１;１,ｂ） 时,给出了可靠度的多层 Ｂａｙｅｓ 估计。     

基于实数编码的改进遗传算法在结构可靠度中的应用研究

本文将人工智能的关键技术之一演化算法中的遗传算法用于结构可靠度的计算,并在算法中采用实数编码技术及一系列目前较先进的策略和算子,同时将模拟退火的思想引入变异算子。通过算例证明这种改进遗传算法在求解可靠度尤其求解复杂非线性问题可靠度时具有良好收敛性和高效性。     

基于改进云图法的高土石坝抗震可靠度分析

高土石坝抗震可靠度研究对大坝抗震防灾和震害风险研究具有重要意义。通过考虑地震动和筑坝料参数双重随机性,建立基于地震易损性和地震峰值加速度概率密度函数的高土石坝抗震可靠度模型,为研究不同设计使用年限的高土石坝抗震可靠度提供依据。通过拉丁抽样方法选取筑坝料参数样本并与选择地震动组合成样本对,选取坝顶相对震陷率作为性能参数,提出考虑抗震设防标准的高土石坝性能水平了;采用SWANDYNE Ⅱ程序进行动力计算,并根据改进云图法得到不同地震峰值加速度下坝顶相对震陷率的地震易损性三维曲面;结合糯扎渡高土石坝不同设计年限的概率分布函数与地震易损性曲面,确定不同设计年限失效概率和抗震可靠度。分析结果表明:随着设计使用年限增加,大坝各个性能水平可靠度不断减小,对于严重破坏状态下不同设计年限可靠度均能满足《水利水电工程结构可靠性设计统一标准》规范要求,说明糯扎渡高土石坝在变形方面抗震设计是合理的。     

An inverse reliability analysis method for reliability-based design optimization with random and dependent interval variables constrained within ellipsoids

In practical design problems, interval variables exist. Many existing methods can handle only independent interval variables. Some interval variables, however, are dependent. In this work, dependent interval variables constrained within a multi-ellipsoid convex set are considered and incorporated into reliability-based design optimization (RBDO). An efficient RBDO method is proposed by employing the sequential single-loop procedure, which separates the coupled reliability analysis procedure from the deterministic optimization procedure. In the reliability analysis procedure, a single-loop optimization for the inverse reliability analysis is performed, and an efficient inverse reliability analysis method for searching for the worst-case most probable point (WMPP) is developed. The search method contains two stages. The first stage deals the situation where the WMPP is on the boundary of the feasible region, while the second stage accommodates the situation where the WMPP is inside the feasible region by interpolation. Three examples are used for a demonstration.     

Reliability analysis and reliability-based design optimization of roadway horizontal curves using a first-order reliability method

This article presents reliability analysis and reliability-based optimization of roadway minimum radius design based on vehicle dynamics, mainly focusing on exit ramps and interchanges. The performance functions are formulated as failure modes of vehicle rollover and sideslip. To accurately describe the failure modes, analytical models for rollover and sideslip are derived considering nonlinear characteristics of vehicle behaviour using the commercial software TruckSim. The probability of an accident is evaluated using the first-order reliability method and numerical studies are conducted using a single-unit truck model. To propose a practical application for the study, the reliability analysis for the minimum radius recommended by American Association of State Highway and Transportation Officials is conducted. The results show that, even if there are deviations from assumed design conditions of the current design guideline, the proposed design method can guarantee given target margins of safety against rollover and sideslip. Based on the reliability analysis, reliability-based design optimization is carried out and the results indicate new recommendations for minimum radii satisfying given target reliability levels.     

System reliability and sensitivity factors via the MPPSS method

A procedure is presented for obtaining the reliability of series, parallel, and mixed systems. The method, called Most Probable Point System Simulation (MPPSS) is simple, and numerically-based. We do not make any claims of analytic advance. Nevertheless, the procedure is more accurate than current analytically-based bounding methods (e.g. bi-modal) and it is computationally efficient. In addition, the method can be used to obtain system sensitivity factors, that is, the importance of each random variable to the system reliability. The procedure is demonstrated through three example illustrations.     

Influence of probability distribution of loads on optimum reliability

Since the Hyogoken-Nambu earthquake, people have begun to pay attention not only to a building's ultimate limit state, but also to its various limit states before collapse through its lifetime. One method to determine optimum reliability has been proposed on the basis of the minimum total cost concept. Load effects are often discussed regarding modeling for probabilistic analyses. Parameters for the probabilistic model, such as the coefficient of variation, the upper bound limit and the characteristics of tail probability, are thought to be important for probabilistic analyses. The purpose of this study is to clarify the effect of these factors on the optimum reliability index, the life-cycle cost and the design point. Numerical investigations have revealed that these factors sometimes significantly affect the optimum reliability, but not the life-cycle cost or the design point for both single and multiple limit states. The minimum total cost concept provides a stable design point with optimum reliability for different load probability models.     

A cuckoo search algorithm by Lévy flights for solving reliability redundancy allocation problems

A new metaheuristic optimization algorithm, called cuckoo search (CS), was recently developed by Yang and Deb (2009 Yang, X.S. and Deb, S., 2009. Cuckoo search via Lévy flights. In: Proceedings of world congress on nature &; biologically inspired computing (NaBIC 2009), 9–11 December 2009, Coimbatore, India. Piscataway, NJ: IEEE Press, 210–214.[Crossref] , [Google Scholar], 2010 Yang, X.S. and Deb, S., 2010. Engineering optimisation by cuckoo search. International Journal of Mathematical Modelling and Numerical Optimisation, 1, 330–343. doi: 10.1504/IJMMNO.2010.035430[Crossref] , [Google Scholar]). This article uses CS and Lévy flights to solve the reliability redundancy allocation problem. The redundancy allocation problem involves setting reliability objectives for components or subsystems in order to meet the resource consumption constraint, e.g. the total cost. The difficulties facing the redundancy allocation problem are to maintain feasibility with respect to three nonlinear constraints, namely, cost, weight and volume-related constraints. The redundancy allocation problems have been studied in the literature for decades, usually using mathematical programming or metaheuristic optimization algorithms. The performance of the algorithm is tested on five well-known reliability redundancy allocation problems and is compared with several well-known methods. Simulation results demonstrate that the optimal solutions obtained by CS are better than the best solutions obtained by other methods.