A probabilistic model of bathing beach safety

An improved mathematical model for bathing beach safety is proposed. It is derived by joining the probability of infection from a given dose (Poisson distribution and the probability of acquiring such a dose (lognormal distribution).Even in the absence of better clinical and epidemiological data, the model permits an assessment of relative risk from certain hazards and the design of more meaningful bacteriological standards for individual beaches.     

Long-term damage of historic masonry: A probabilistic model

Creep and the creep-fatigue interaction have shown to strongly influence the mechanical behaviour of ancient masonry and long-term heavy loads proved to cause a continuous damage. The problem of achieving a reliable life-time estimate of historic masonry toward the effects of persistent loading has been dealt with by a probabilistic approach. The results of pseudo-creep tests on ancient masonry of different ages and their interpretation through a probabilistic model are presented, aimed to the individuation of a random variable as a significant index of vulnerability, and to the solution of the classic problem of reliability in stochastic conditions.     

A space-time probabilistic model for pipe network reconstruction planning

A space-time probabilistic model can be combined with a dual objective management model to rank reconstruction strategies for a water supply pipe network. The network is characterised by similar age and environmental and traffic conditions. A homogeneous spatial Poisson process represents the location of pipe failures, while the number of failures is modelled by a non-homogeneous Poisson process. Thus, a space-time Poisson process describes failure probabilities in space and time. A simulation procedure is used to generate failure patterns in any time and estimate expected costs and expected failure consequences. A dual objective management model may be developed to aid ranking reconstruction strategies for a selected time horizon aiming at minimising cost and failure impact. A Failure Impact Index FI is formulated by calculating the areal extend of unacceptable pressure drops due to individual failures. The results indicate a trade-off exists between cost and FI.     

A probabilistic fatigue strength model for brick masonry under compression

The paper presents the development of a model for the fatigue resistance of brick masonry under compression. The model takes into account the random nature of the fatigue strength phenomena and, as a consequence, proposes different model parameters as a function of the desired probability level. The model, based on a Weibull distribution, has been calibrated with the still limited experimental data on brick masonry under high cycle compression loading. Very good correlation is obtained. The results show that there is a clear trend of the experimental data to follow the Weibull distribution. It is also shown how the fatigue resistance of brick masonry is not only dependent on the magnitude of the stress cycles, but also on the magnitude of the minimum stress level. The paper also shows how the proposed model can be used in the reliability-based assessment of the fatigue performance of existing masonry arch bridges. Either the nominal probability of failure (reliability index) to fatigue or the remaining service life with a predefined probability level for an existing bridge can be predicted with the proposed method.     

A comprehensive probabilistic model of chloride ingress in unsaturated concrete

Corrosion induced by chloride ions has become a critical issue for many reinforced concrete structures. The chloride ingress into concrete has been usually simplified as a diffusion problem where the chloride concentration throughout concrete is estimated analytically. However, this simplified approach has several limitations. For instance, it does not consider chloride ingress by convection which is essential to model chloride penetration in unsaturated conditions as spray and tidal areas. This paper presents a comprehensive model of chloride penetration where the governing equations are solved by coupling finite element and finite difference methods. The uncertainties related to the problem are also considered by using random variables to represent the model’s parameters and the materials’ properties, and stochastic processes to model environmental actions. Furthermore, this approach accounts for: (1) chloride binding capacity; (2) time-variant nature of temperature, humidity and surface chloride concentration; (3) concrete aging; and (4) chloride flow in unsaturated conditions. The proposed approach is illustrated by a numerical example where the factors controlling chloride ingress and the effect of weather conditions were studied. The results stress the importance of including the influence of the random nature of environmental actions, chloride binding, convection and two-dimensional chloride ingress for a comprehensive lifetime assessment.     

A probabilistic framework based on statistical learning theory for structural reliability analysis of transmission line systems

This paper describes a novel application of statistical learning theory to structural reliability analysis of transmission lines considering the uncertainties of climatic variables such as, wind speed, ice thickness and wind angle, and of the resistance of structural elements. The problem of reliability analysis of complex structural systems with implicit limit state functions is addressed by statistical model selection, where the goal is to select a surrogate model of the finite element solver that provides the value of the performance function for each conductor, insulator or tower element. After determining the performance function for each structural element, Monte Carlo simulation is used to calculate their failure probabilities. The failure probabilities of towers and the entire line are then estimated from the failure probabilities of their elements/components considering the correlation between failure events. In order to quantify the relative importance of line components and provide the engineers with a practical decision tool, the paper presents the calculation of two types of component importance measures. The presented methodology can be used to achieve optimised design, and to assess upgrading strategies to increase the line capacity.     

Improving project outcomes through operational reliability: A conceptual model

The work reported here is part of an on-going research effort concerned with developing a methodology to improve the outcomes of projects involving complex information systems. To facilitate the study, previous research concerned with high reliability organisations (HRO) is examined. An analysis of this literature is used to develop a conceptual model that explains how highly reliable operational capabilities are achieved and maintained. Cases of catastrophic failures are evaluated using this paradigm to illustrate its utility as an analytical research tool and its potential as a systemic framework for evaluating the operational capability of organisations prior to project initiation.     

A probabilistic model for chloride-ingress and initiation of corrosion in reinforced concrete structures

Corrosion of the reinforcement is a major problem for a large number of reinforced concrete structures because it can lead to a substantial decrease of the load-bearing capacity. One mode of corrosion initiation is that the chloride content around the reinforcement exceeds a critical threshold value. In the present paper a statistical model by which the chloride content in a reinforced concrete structure can be predicted, is developed. The model parameters are estimated on the basis of measurements. The distribution of the time to initiation of corrosion can now be estimated by traditional FORM/SORM-analysis. The model can also be used to determine optimal repair and maintenance strategies. In a number of examples these applications are illustrated.     

A probabilistic model for the assessment of uncertainties in the shear strength of rock discontinuities

Discontinuity shear strength plays a critical role in many problems encountered in rock engineering, especially in the design of rock slopes. Since its precise estimation is generally not possible, it is crucial that the errors and uncertainties associated with its estimate be quantified and reflected in the design procedure. In this study, the uncertainties underlying discontinuity shear strength are thoroughly examined and an uncertainty analysis model is developed for the estimation of in situ discontinuity shear strength with a special emphasis on rock slopes. An extensive literature survey on shear behavior of unfilled rock discontinuities has been carried out and the necessary data for the quantification of uncertainties are extracted from this survey. These uncertainties stem from the discrepancies between laboratory-measured and in situ discontinuity shear strength values, as well as from the inherent variability of shear strength within a rock medium. The main causes of discrepancies, namely, scale, anisotropy and water saturation are considered. For each source of discrepancy a correction factor, treated as a random variable, is assigned and guidelines for the quantification of the statistical parameters of these correction factors are presented within the framework of the proposed uncertainty analysis model. The proposed uncertainty model provides an analytical tool for the systematic treatment of uncertainties involved in the estimation of the in situ value of peak friction angle from the laboratory test results.     

装备研制可靠性工作项目风险评估综合模型

武器装备研制作为军事战略的重要组成部分,对军队战斗力的形成有着十分重要的影响。装备研制可靠性工作项目必须要用科学的方法来指导,目的是能够确定正确的武器装备研制决策,为军队提供坚实的物质技术基础。总结了用风险影响图分析问题的思想,综述了层次分析法的优缺点,对装备研制可靠性工作项目风险评估做了介绍。     

A probabilistic risk analysis technique with an application to enclosure fires

A new technique for solving stochastic differential equations is described and illustrated by an application to a simple theory of enclosure fires. The relevance of this technique to the prediction of complex processes in accidental fires is discussed.     

A model for determination of motor vehicle emission factors from on-road measurements with a focus on submicrometer particles

The multiplicity of parameters that influence traffic-related emissions and that are often very difficult to measure or predict, makes the assessment of traffic emissions a very complicated process, strongly dependent on local conditions and usually associated with a high degree of error. The aim of this paper was to develop, calibrate and test a simple model for 'on-road' measurements of traffic emission factors as part of a major program focussed on the assessment of traffic contribution to fine and ultrafine emissions to the whole air shed and to local areas in south-east Queensland, Australia. A mathematical model developed was based on the mass balance concept for on-road assessment of traffic-related emission rates. The model requires fewer experimental data points as input and is more applicable to the common on-road testing situation, when no more than two monitors of a specific pollutant can be used. The model was tested and calibrated using experimental data on particle number concentration collected at a road-monitoring site using the scanning mobility particle sizer, and was applied to assess the emission factors of submicrometer particles emitted by traffic. The average emission factor obtained using the box model and the experimental data from road measurements was 1.75 x 10(14) particles km(-1) vehicle(-1), with a standard error of 67.6%. While the emission factor obtained was comparable with some results obtained from dynamometer studies and applied to the vehicle mix at the sampling site, they were significantly higher than the factors reported by other studies.     

高速铁路900t级模块式运梁车的改进方案

从秦沈客运专线运架混凝土箱梁的实践，笔者深感应大力推广采用通用的模块式运输车运梁，以取代专用的中梁式运梁车。一台轮胎式运梁车，与相配套的同吨级架桥机相比，虽自重仅为后者的1／2～1／3，但购置费却高出10％～20％。中铁二局进口的一台550t Nicola中梁式运梁车，可运24m双线梁，中铁四局购置国产450t中梁式运梁车，可运32m单线箱梁，但二者今后都难于在需架32m双线梁的京沪高速铁路中发挥作用，这就是重型专用运梁车的共同缺点。克服此缺点的办法就是采用模块式运输车，既可组合后运900t重的高速铁路的32m梁，又可适应不同的运输需要作不同的分解组合。     

A new model for effects of impersistent joint sets on rock slope stability

Joints often have profound effects on elastic properties and strength of rock masses and therefore on rock slope stability. In surface mine slopes, joints are usually too numerous to be taken into account individually, so an equivalent properties approach is necessary. Previous work that treats a jointed rock mass as an equivalent composite material of joints and intact rock between resulted in excellent agreement between estimated and true rock mass elastic moduli in case of fully persistent joints, for example, [Pariseau WG. An equivalent plasticity theory for jointed rock masses. Int J Rock Mech Min Sci 1999;36(7):907–18]. Rock mass failure mechanisms on joints and through intact rock were retained using influence functions obviating the need for an equivalent rock mass strength. Impersistent joints, which are not continuous on a joint plane, can be accommodated [Pariseau WG. Effects of joint persistence on jointed rock masses. Trans Soc Min Metal Explor 2003;314:121–8]. However, slope stability analysis of a large, deep copper mine indicated a need for computational efficiency even in two-dimensional analysis of vertical sections through pit walls [Puri S. Role of joint persistence in rock slope stability. MS thesis, Department of Mining Engineering, University of Utah, 2006]. The analyses by the popular finite element method used small elements of bench size near the pit slopes and much larger elements away from the pit walls. The reasons for the graded meshes were numerical accuracy (small elements) and computational economy (large elements). Small elements contained only a few joints, while the larger elements contained hundreds of joints and led to impractical computation run times, on the order of days. A new modeling procedure that recognizes sufficiently large elements as representative volume elements (RVEs) assists in overcoming this obstacle. A companion improvement embeds a sufficient number of joints in RVE-size elements that then allows for recovery of joint failure mechanisms that are lost with the RVE designation. These innovations reduced PC (Pentium-4) run times by two orders of magnitude to a few hours.     

中外合资一体化工程项目管理模式实践分析

通过中外合资大型石油化工项目的一体化工程项目管理模式的实践,总结了实施一体化工程项目管理模式的优点和缺点,分析了选择一体化工程项目管理模式的条件,为社会上类似项目的管理提供一定的参考。     

带横缝高混凝土拱坝动力模型试验研究

在我国西南地震高发区建设高混凝土拱坝,大坝的抗震安全是一个非常重要的课题。通过振动台动力模型试验,研究带横缝高混凝土拱坝在地震荷载作用下从弹性变形到最终破坏的动力特性。试验表明,带横缝拱坝与整体拱坝的动力特性及破坏形态均有所不同。     

弦杆受压大直径空间相贯节点足尺模型试验与设计研究

针对贵阳奥体中心主体育场罩篷空间钢管桁架屋盖中的上、下弦相贯节点,进行了足尺节点破坏试验。详细介绍了试验方案、过程、现象和结果。根据试件的受力全过程特点,进行了试验数据分析,了解各加载阶段相贯节点的应力分布情况,得出了此工程节点的破坏模式。并运用有限元软件,从应力、应变和位移三方面对钢管相贯节点进行全过程屈曲分析。揭示了相贯节点的受力性能、塑性区的扩展过程和节点区的应力、应变分布状态,进一步确定了空间相贯节点的破坏准则和承载力确定准则。将节点试验结果、有限元计算结果和规范计算结果进行了对比,并对空间相贯节点的空间相关性予以分析和探讨。     

弦杆受拉大直径空间相贯节点足尺模型试验与设计研究

以贵阳奥体中心主体育场工程为背景,针对空间钢管桁架屋盖受拉上弦相贯节点,进行足尺节点极限承载力破坏试验。对节点试验过程和破坏现象进行了深入研究,分析了各加载阶段相贯节点的应力分布情况及整个加载过程塑性区的开展过程,结合有限元分析对空间相贯节点破坏机理进行分析研究,并应用有限元软件模拟试验加载过程进行非线性计算,分析节点破坏准则。按提出的节点设计承载力准则判定节点设计承载力,并与规范计算值进行比较。针对规范主弦杆受拉则不考虑主弦杆轴力变化对节点承载力的影响,进行主弦杆轴力变化对节点承载力影响的非线性有限元分析,并与规范计算值比较。研究表明,无论支弦杆受拉或受压,随主弦杆拉力的增加,节点承载力逐渐降低。