可变作用代表值的线性回归推断方法

为克服实际工程中测试数据不足情况下,采用经典统计学方法推断可变作用的代表值时,由统计不确定性导致推断结果偏小的缺点,利用可变作用服从极大值I型分布,与极小值I型分布可相互转换的特性,根据极小值I型分布分位值的线性回归推断方法,提出了可变作用标准值、频遇值的线性回归推断方法,可在不同的置信度下考虑统计不确定性的影响,适用于小样本统计。分析结果表明:小样本条件下,按点估计法推断可变作用的标准值和频遇值时,结果偏小;按线性回归推断方法推断可变作用的标准值、频遇值和设计值时,可取置信度为0.75;可变作用的准永久值受统计不确定性的影响较小,可取点估计法的推断结果。     

楼面活荷载、风荷载的频遇值和准永久值的确定

现行GB50009-2001《建筑结构荷载规范》规定的频遇值系数和准永久值系数是根据工程经验确定的,没有严格的统计基础。针对此种情况,按照GB 50009—2001的统计定义,建立频遇值系数和准永久值系数与平均超越时间和设计基准期比值的关系,得到楼面活荷载和风荷载的频遇值系数和准永久值系数。按统计方法得出的楼面活荷载频遇值系数比GB 50009—2001规定的值稍大,其准永久值系数比GB 50009—2001规定的值小,风荷载频遇值系数则稍大于规定。     

采用频遇值的预应力混凝土抗裂性设计可靠度分析

提出了频遇值的概念,并通过作者自编的程序应用MONTE－CARLO方法模拟频遇值的实际分布,得出了频遇值的统计参数, μ,σ。采用频遇值,以预应力混凝土的抗裂性设计为例,进行了可靠度分析。     

钢筋混凝土水池受弯构件裂缝宽度可靠度分析

钢筋混凝土水池受弯构件裂缝宽度的可靠度与可变作用与永久作用的比值、准永久值系数综合值和配筋率有密切的关系。首先建立极限状态方程,采用蒙特卡罗法,分析了四组不同截面的构件在不同作用比、不同准永久值系数综合值和不同配筋率下,钢筋混凝土水池受弯构件按强度配筋下裂缝宽度的可靠度。结果表明:可靠指标随可变作用与永久作用的比值、配筋率的增大而增大,随构件截面、准永久值系数综合值的增大而减小。     

工业建筑可变作用的概率模型及可靠度

对工业建筑可变作用的概率模型及可靠度研究现状进行了综述,包括工业建筑可变作用的概率模型、工业建筑设计可靠度、既有工业建筑鉴定评级可靠度、工业建筑时变可靠度4个方面,揭示了当前研究的不足。工业建筑可变作用包括吊车荷载、工业建筑楼面活荷载和屋面积灰荷载,当前我国相关技术标准中荷载标准值的取值虽是建立在实测统计资料基础上的保守值,但对吊车荷载及荷载效应的概率模型仅做了初步研究,对工业建筑楼面活荷载和屋面积灰荷载的概率模型目前尚未有研究。工业建筑设计的目标可靠指标是以民用建筑设计校准结果为依据给定的,设计可靠度、鉴定分级可靠度的校准工作均采用民用建筑的可变作用和3种简单荷载组合,未考虑工业建筑特殊可变作用,校准结果是保守和粗略的。工业建筑时变可靠度涉及结构耐久性和吊车梁疲劳问题,是工业建筑全寿命可靠性分析与控制的理论基础,应给予足够重视。     

结构可靠度的时段分析方法

当结构可靠度的分析涉及多个荷载效应的组合时,目前多采用JCSS根据Turkstra规则推荐的组合方法,该法在国际、国内标准中都得到了应用。本文通过研究发现,这种方法与其所采用的荷载效应概率模型是不相符的,而且会导致结构可靠度的分析结果偏于冒进。为此文中提出了结构可靠度的时段分析方法,它不仅与荷载效应概率模型完全相符,而且不必采用经验方法进行荷载效应组合,组合问题已融入结构可靠度的计算之中;同时该法还具有较强的通用性,可应用于抗力为随机过程时的情形,以及抗力、荷载效应随机过程具有非平稳性和相关性时的情形。     

交叉井字梁楼面汽车荷重等效均布活荷载的换算

建筑物的楼面上或地下室顶板常因消防等原因需通行车辆而直接承受车辆荷重。我国《建筑结构荷载规范》(GB50009-2001)提出了汽车通道处楼面均布活荷载的标准值、组合值、频遇值和准永久值系数。本文结合实际工程对此问题进行探讨,供设计人员参考。     

夯实水泥土桩复合地基承载力可靠度分析

根据Vanmarche提出的随机场理论,以夯实水泥土桩为例建立了复合地基极限状态方程,对随机变量的概率模型进行了分析,结合工程实例采用JC法进行复合地基承载力的可靠度分析,给出了可靠度指标与置换率、桩间土发挥系数、荷载比及随机变量的变异性之间的关系。     

基坑设计时坑边超载取值问题的探讨

统计了基坑工程所涉及到的建筑材料和施工机械的超载值,介绍了相关规范中承载能力极限状态和正常使用极限状态用于基坑工程时的分项系数取值问题,认为正常使用极限状态下各种建筑材料、长期放置的施工设备等超载可采用组合值;土方运输车辆、商砼罐车等荷载可根据实际情况采用频遇值或准永久值,并建议了超载的各种代表值系数。提出基坑设计中应根据实际情况,计算各种超载的具体数据,从而降低基坑工程的风险。     

基于多元非线性回归的隧道结构可靠度及敏感性分析

针对隧道衬砌结构可靠度分析中功能函数难以显式表达的特点,类比响应面法提出了一种较为实用的可靠度计算方法。该方法利用ABAQUS非线性有限元分析及Origin数据处理的优势,拟合出各参数的单一随机变量函数,进行敏感性分析,从中提取能反映结构响应与随机变量变化关系的有价值因子进行组合。最后利用多元线性或非线性回归求出待定系数的值,得到满足工程要求的显式功能函数,进而用编制的一次二阶矩法可靠度指标计算程序进行可靠度计算。     

Redundancy-based service life assessment of corroded reinforced concrete elements considering parameter uncertainties

In order to assess the structural reliability and redundancy with respect to deterioration, appropriate models have to be selected which adequately describe the deterioration process. The parameters associated with these models have to be estimated based on statistical inference. In general, the uncertainties that arise from the estimation of parameters are not accounted for in reliability assessment and the obtained structural reliability indices are assumed to be constant values. When parameter uncertainties are considered, the structural reliability index can, however, be considered as a random variable which inevitably influences the full-probabilistic decision-making process. Furthermore, the structural reliability indices which are used in a reliability-based redundancy factor can be considered as random variables. Hence, this redundancy factor itself is a random variable as well. In this paper, a full-probabilistic framework is developed which allows for the service life assessment of reinforced concrete elements subjected to corrosion based on a probability-based redundancy factor and taking into account parameter uncertainties. It is proven that these parameter uncertainties have a significant influence on the lifetime estimates of concrete elements subjected to corrosion. Finally, a simplified method is proposed which allows to incorporate parameter uncertainties in the redundancy assessment.     

Methods of reliability model updating through additional events

Reliability theory is now applied in various areas. A first-order or second-order reliability method gives good approximations to both component and system reliability computations. With these available techniques, reliability models conditioned on additional events can be updated. Existing approaches to this important aspect of the reliability analysis are found numerically involved. New analytical methods, which are both theoretically reasonable and numerically efficient, are thus developed for computing the updated reliability as well as the updated distributions of the basic variables affecting the reliability. Especially, it is found that the distribution of an independent normal or lognormal variable, or the joint distribution of a group of normal or lognormal variables, is invariant through updating. Only its characteristic values need updating. Numerical examples for proof-loading and non-destructive inspection are also illustrated.     

Reliability assessment of reinforced concrete structures based on random damage model

A stochastic model is developed to describe the fracture behaviour of concrete fibres at micro-level, and a probabilistic relation between the fibre strain and the concrete damage variable is established. In this context, the concrete damage evolution can be quantified by two representative random variables. In this regard, the number of random variables employed in potential reliability assessment studies can be greatly reduced. The accuracy of the proposed method is verified by comparing the first- and second-order moments of the stochastic damage evolution with the corresponding closed form solutions. Further, the proposed method is applied to the non-linear analysis and reliability assessment of a five-story reinforced concrete frame, and the results show that it is quite efficient for stochastic response determination and reliability evaluation of complex structures.     

Probability density evolution analysis of stochastic nonlinear structure under non-stationary ground motions

In the present paper, a framework of dimension-reduction modeling method is developed for a dual stochastic dynamic structural system of spectrum-compatible non-stationary stochastic ground motion processes and stochastic structures. With the aid of the proposed method, the random variables used to describe the stochastic characteristics of the non-stationary ground motion processes and the structural parameters are respectively represented by the one-elementary-random-variable functions, contributing to an entire stochastic dynamic structural system readily described by merely two elementary random variables. Owing to the fact that the number of the elementary random variables needed is extremely small, the set of the representative points associated with the elementary random variables can thus be selected by the widely-used number theoretical method, and then the probability density evolution method can be conveniently combined to conduct the dynamic response analysis and dynamic reliability evaluation of nonlinear stochastic structures. In the numerical examples, the probability density evolution analysis of an eight-storey reinforced concrete frame structure with random parameters subjected to spectrum-compatible non-stationary stochastic ground motion processes is investigated as a case study. Numerical results fully demonstrated the effectiveness and robustness of the proposed method.     

基于强度折减的边坡抗滑桩可靠性分析

为了对边坡抗滑桩加固工程进行合理的设计,建立位移迭代有限元模型模拟桩-土间的相互作用,基于强度折减的位移迭代有限元法对边坡抗滑桩加固工程进行可靠性分析,把计算参数视为随机变量考虑参数变异性对抗滑桩锚固深度及边坡加固工程可靠性的影响。可靠指标的选取应考虑边坡工程等级,以目标可靠度为控制指标去指导抗滑桩锚固深度的设计。工程...     

工字形截面钢结构可靠性分析

以工字形截面的屈服应力和外荷载为随机变量 ,在满足稳定性条件下 ,进行结构可靠性分析。采用随机有限元法求解非线性安全余量可靠性指标和失效模式间的相关系数 ,为满足稳定性的工字形截面钢梁的结构可靠性分析提供一种合理方法     

同时考虑基本变量和极限状态模糊性的边坡模糊随机有限元可靠度分析

 基于边坡稳定有限元分析的滑面应力法,研究同时考虑基本变量模糊性和极限状态模糊性的边坡稳定模糊随机有限元可靠度分析方法。对于基本变量的模糊性,采用等价变换的方法将模糊变量等价变换为随机变量;对于极限状态的模糊性,基于概率积分法研究了模糊破坏概率及模糊随机可靠指标的求解方法。本方法既可求解边坡剖面上各有限单元的模糊随机可靠指标,亦可求解边坡整体最小可靠指标及临界滑面的位置;既可考虑基本变量的模糊性,又可考虑极限状态的模糊性,是常规的随机有限元可靠度分析方法的推广。当不考虑基本变量和极限状态的模糊性时,它即退化为随机有限元可靠度分析方法。     

Structural dynamic optimal design based on dynamic reliability

In this work, dimension and shape optimization of structures under stochastic process excitation is addressed in the context of element or system dynamic reliability constraints, where the structural gross mass is taken to be the objective function. Firstly, based on the dynamic response analysis of truss structures under stochastic process loads, the dynamic reliability constraints are developed and simplified, and the normalization of design variables is discussed to avoid some variables being drowned by others during optimization due to their different dimensions and orders of magnitude. The optimal models of dimension and shape with element or system dynamic reliability constraints are then presented. Two numerical examples are finally used to illustrate the results of different optimal designs, which demonstrate that the efficiency to solve the structural optimization with dynamic reliability constraints can be significantly improved if the design variables and their initial values are selected properly.     

Methods for approximate reliability analysis

Approximate solutions are developed for reliability problems involving constant-in-time and time-dependent random parameters. They are based on estimates of the distribution of scalar control variables obtained from approximations of the safety condition (control variable approach) or on a transformation of the input space of parameters into a space in which the safety condition is nearly linear (linearization approach). The distribution of the control variable or of the random parameters in the transformed space can be estimated from moments of these variables. The control variable approach is most effective when the random parameters are constant in time while the linearization approach is useful for time-dependent reliability studies since it permits application of various rules (e.g., Turkstra's rule) for approximate load combination analysis.