体系可靠指标对随机变量分布参数的敏感性

目前,在体系可靠指标对随机变量的敏感性分析中,没有考虑失效模式间的相关系数对随机变量的敏感性。针对这个问题,通过理论推导,得到了失效模式间的相关系数对随机变量的敏感性,进而修正了体系可靠指标对随机变量的敏感性表达式;根据敏感性定义及参考现行规范,提出了随机变量作为常量的判断标准。算例结果表明,修正的体系可靠指标对随机变量的敏感性表达式是正确的,提出的随机变量作为常量的标准是可行的。因此,本研究完善了体系可靠指标对随机变量的敏感性分析方法,为提高结构体系可靠指标的计算效率提供了理论依据。     

求解概率型网络计划时差问题的一种计算模型

对概率型网络计划问题,目前国内外的研究重点是网络计划的计算工期的估计和关键性的确定方面,对于线路和工作时差问题研究的较少,并且都是基于确定型网络计划时差的研究,而时差又是利用网络计划进行工程项目进度控制的一个重要参数。文章结合随机优势的思想,提出一种计算概率型网络计划线路和工作时差的计算模型,为概率型网络计划的时差问题提供了一些参考。     

随机变量相关性对隧道二衬作用效应的研究

地下工程中岩土层自身的随机性、模糊性及不确定性因素使得隧道工程面临着较大风险。随着隧道工程的蓬勃发展,如何提高隧道工程衬砌结构的安全度、降低工程结构风险措施的研究显得尤为重要。然而,直至目前仍然没有系统、科学的方法来降低隧道工程风险。本文以可靠度理论为基础,同时基于ANSYS软件中的PDS技术,对隧道工程中二衬结构的某些参数的相关性入手,探讨随机输入变量的相关系数对二衬结构的作用效应的影响。研究成果表明:忽略随机变量之间的相关性将对计算结果造成很大误差;二衬作用效应与计算参数的相关系数之间存在一定的线性关系;隧道设计中应当考虑计算参数间的相关性才能使工程设计更贴近真实情况。     

拟建结构和现有结构的抗力概率模型

完善了结构抗力的随机过程概率模型,对独立增量过程概率模型作了更深入的阐述,并论述了抗力概率模型应满足的基本条件。针对拟建结构和现有结构之间的差别,文中还建立了不同结构具体的抗力概率模型,在现有结构抗力的概率模型中引入了未确知量,以反映人们在认识现有结构当前抗力时的未确知性。文中的抗力概率模型不仅解决了自相关系数难以统计的困难,而且在结构可靠性的分析中可以得到偏于保守的结果。     

Highway and Road Probabilistic Safety Assessment Based on Bayesian Network Models

A Bayesian network model is developed, in which all the items or safety related elements encountered when traveling along a highway or road, such as terrain, infrastructure, light signals, speed limit signs, intersections, roundabouts, curves, tunnels, viaducts, and any other safety relevant elements are reproduced. Since human error is the main cause of accidents, special attention is given to modeling the driver behavior variables (driver's tiredness and attention) and to how they evolve with time or travel length. The sets of conditional probabilities of variables given their parents, which permit to quantify the Bayesian network joint probability, are obtained and written as closed formulas, which allow us to identify the particular contribution of each variable to safety and facilitate the computer implementation of the proposed method. In particular, the probabilities of incidents affecting safety are calculated so that a probabilistic safety assessment of the road can be done and its most critical elements can be identified and sorted by importance. This permits the improvement of road safety making adequate corrections to save time and money in the maintenance program by concentrating on the most critical elements and effective investments. Some real examples of a Spanish highway and a conventional road are provided to illustrate the proposed methodology and show its advantages and performance.     

基于“服务水平”概念的路网总体容量计算模型

引入"路网服务水平"概念,建立不同路网服务水平条件下的交通网络总体容量计算模型;根据交通流基本参数速度—流量—密度之间的基本关系,建立不同服务水平下各级道路的车流密度计算模型;进而确定道路交通网络系统所能承受的车辆数以及交通系统所能适应的交通需求总量,并结合青岛市城市综合交通规划,给出了路网容量计算实例.     

建筑物理模型与结构分析模型的数据映射研究

本文围绕AEC/FM领域应用软件的信息共享与互用,探讨了建筑建模软件与结构分析软件间的数据映射方案。基于IFC(Industry Foundation Classes)标准,分析了建筑物理模型与结构分析模型的异同,提出了从IFC建筑物理模型文件中提取结构构件以及结构构件连接节点拓扑信息的方法,并基于这些映射算法,利用C++编程语言实现了本文提出的通用结构分析模型(SGF)与IFC建筑物理模型的双向数据接口。最后,提出了以SGF为中心的多种建筑物理模型与多种结构分析模型的数据集成基本框架。     

浅析城市交通拥挤现象及解决方法

随着城市化进程的加快,城市交通需求量急剧增加,交通拥挤已成为我国大中城市的普遍问题。交通拥挤不仅造成了城市巨大的经济损失,而且影响了居民的生活质量,可以说交通拥挤已成为制约城市经济发展的瓶颈。文章在分析我国城市道路交通拥挤的原因的基础上,提出了解决城市交通拥挤的措施。     

Proactive,Backward Analysis and Learning in Road Probabilistic Bayesian Network Models

Some probabilistic safety assessment models based on Bayesian networks have been recommended recently for safety analysis of highways and roads. These methods provide a very natural and powerful alternative to traditional approaches, such as fault and event tree based methods. In this article, we present several new and original contributions to complement the inference engine tools of these models to provide new and relevant information about safety and backward analysis on one hand, and to learn the complex multidimensional joint probabilities of all variables, on the other hand. More precisely, we show how standard tools combined with the partitioning technique can be used in new ways to solve three relevant problems (1) to prognosticate the most probable combinations of variables leading to incidents, (2) to perform a backward analysis to identify the causes of accidents, and (3) to learn the model parameters using Bayesian conjugate methods (categorical and Dirichlet families). Finally, some real examples of applications are used to illustrate the proposed methods.     

半刚接钢框架系统刚度可靠性对随机变量的敏感性分析

本文将梯度优化法与有限元法相结合,研究了结构失效模式可靠度对隐式随机变量的敏感性,并用PNET法分析了结构系统刚度可靠度对随机变量的敏感性。通过三个算例,对影响半刚接钢框架系统刚度可靠度的多个随机变量进行了敏感性分析,结果表明:在中高层钢框架中,结构系统刚度可靠度对连接刚度Rk的均值敏感性更为显著,而对其变异系数和分布类型的敏感性较小,在结构设计中应慎重考虑。     

Microscopic Models and Network Transformations for Automated Railway Traffic Planning

This article tackles the real‐world planning problem of railway operations. Improving the timetable planning process will result in more reliable product plans and a higher quality of service for passengers and freight operators. We focus on the microscopic models for computing accurate track blocking times for guaranteeing feasibility and stability of railway timetables. A conflict detection and resolution model manages feasibility by identifying conflicts and computing minimum headway times that provide conflict‐free services. The timetable compression method is used for computing capacity consumption and verifying the stability according to the UIC Capacity Code 406. Furthermore, the microscopic models have been incorporated in a multilevel timetabling framework for completely automated generation of timetables. The approach is demonstrated in a real‐world case study from the Dutch railway network. Practitioners can use these microscopic timetabling models as an important component in the timetabling process to improve the general quality of timetables.     

On the Bicycle Traffic in China

Editor: Min Fengkui's article "Bicycle traffic inChina" in your issue of June 1986 (volume 2number 1) provides a valuable overview ofthe growth of bicycling in China's cities andits relationship to public transportation. Healso offers some interesting proposals re-garding policies to be followed in cities ofvarious sizes with respect to the promotionof bicycling and public transportation. While much of his paper is interestingand useful, we do want to take issue withcertain parts of his analysis as well as with     

Kernel Smoothing Method Applicable to the Dynamic Calibration of Traffic Flow Models

Abstract: Real time traffic flow simulation models are used to provide traffic information for dynamic traffic management systems. Those simulation models are supplied by traffic data in order to estimate and predict traffic conditions in unobserved sections of a traffic network. In general, most of recent real time traffic simulators are based on the macroscopic model because the macroscopic model replicates the average traffic behavior in terms of observable variables such as (time–space) flow and speed at a relatively fast computational time. Like other simulation models, an important aspect of the real time macroscopic simulator is to calibrate the model parameters online. The most conventional way of the online calibration is to add a random walk to the parameters to constitute an augmentation of the traffic variables and the model parameters to be estimated. Actually, this method allows the parameters to vary at every time step and, therefore, describes the adaptation of the model to the prevailing traffic conditions. However, it has been reported that the use of the random walk results in a loss of information and an increase of the covariance of parameters, which consequently leads to posteriors that are far more diffuse than the theoretical posteriors for the true parameters. To this end, this article puts forward a Kernel density estimation technique in the calibration process to handle the covariance issue and to avoid the information loss. The Kernel density estimation technique is embedded in the particle filter algorithm, which is extended to the calibration problems. The proposed framework is investigated using real‐life data collected in a freeway in England.     

Uncertainty Processing and Risk Monitoring in Construction Projects Using Hierarchical Probabilistic Relational Models

Construction projects do not often reach their expected results regarding time, cost, and quality, due to the internal and external environment variations. Despite a substantial literature about risk management, no generic approach is proposed to represent construction project considering together technical and human dimensions or sustainability with their uncertainties. Modeling complex dynamical systems from heterogeneous pieces of knowledge varying in precision and reliability is a challenging task. This article proposes an innovative generic and versatile approach, based on the formalism of hierarchical probabilistic relational models to analyze and to propagate uncertainty in construction project regarding different levels of knowledge. The aim is to obtain a flexible, portable, and versatile model able to simulate the behavior of complex system's entities involved in any construction project at different levels of detail while taking uncertainty into account. To illustrate and highlight this approach, an academic example and a real case are proposed.     

随机交通环境下的轨道交通站点公交接驳优化研究

常规公交是城市居民出行的重要组成部分,做好公交车与轨道交通的有效接驳是城市居民出行效率的重要保证。以乘客与公交接驳运营的广义费用最小为目标函数,综合考虑了公交在城市实际运行过程中的随机性,同时以有限车辆为约束,建立公交接驳优化模型,从而解决在该约束下的公交多线路的资源优化配置问题。最后利用算例证明了模型及算法的有效性。     

关于确定城市交通方式结构的研究

城市交通规划中交通方式结构的研究是十分重要的。但在一些城市的交通规划中 ,交通方式结构的确定带有很大的主观性、缺少说服力。笔者试图运用城市已有的交通调查资料 ,从道路网和公交网的发达程度、道路车速、居民出行距离分布特征、出行时耗、经济收入水平等方面 ,找出城市居民在选择城市公共交通和私人交通工具之间的规律性 ,从而能定量与定性相结合地确定该城市自己的交通方式结构     

广州交通现状及发展探讨

广州现有道路、车辆及周边经济发展对广州交通的影响很大。在城市公共交通以及交通管理等发展的基础上,根据广州市交通现状及存在的问题,从市中心区交通、公共交通、交通管理等方面进行了分析,并从城市总体规划、交通基础设施建设、加强交通需求管理、处理好行人和自行车交通等方面提出建议。     

基于VISUM仿真软件的交通建模研究

对交通建模的目标、定位及基本架构进行了简要分析介绍,列举了建模的基础数据要求,对交通建模的经典四阶段法不同阶段(出行生成、出行分布、出行方式划分、交通分配)的具体理论和方法作了介绍,并提供了交通建模实例应用,可供参考借鉴。