System reliability analysis of existing structures

In this paper a system reliability analysis of existing structures is presented which can account for the structural deterioration and damage resulting from impact, corrosion and crack.     

Safety assessment of existing structures using a filtered fuzzy relation

Most constructed systems, as well as our infrastructure system, require regular inspection and reassessment so that proper actions can be taken to maintain their current usefulness. Although the quantitative information obtained from these inspections can be analyzed systematically and consistently using probability theory, a parallel analysis is not yet developed for the qualitative information obtained. A filtered fuzzy relation algorithm which utilizes the fuzzy set theory is developed to analyze the qualitative data methodologically. The analysis yields a safety function which shows the degree of belonging for each level of safety reduction from the original design reliability. A sensitivity analysis on the membership functions associated with the input data to the resulting safety function is also performed. The results indicate that, in general, the preciseness of these membership functions has little or no influence on the safety functions. Thus the filtered fuzzy relation algorithm has practical application in assessing existing membership functions.     

A fuzzy logic approach to model delays in construction projects using translational models

The likelihood of a project delay is affected by different factors; thus, there is a pressing need to develop a method that estimates the likelihood of such a delay. In this paper, analysis of potential occurrences of delays, which are classified into procedural, enabling, and triggering causes, is performed using the fuzzy fault-tree analysis method. Subjective judgment expresses causes of delay and their respective degree of effectiveness which are analysed in this study. The fuzzy triangular model and translational models are employed in this study. The severity of the likelihood of the project delay is the result of this analysis. A model was developed to assess the likelihood of the project delay. Evaluation of the model was performed for applicability and adequacy of the model. On average, evaluation performed by independent construction engineers and fuzzy logic experts produced satisfactory results.     

A fuzzy logic approach to model delays in construction projects using rotational fuzzy fault tree models

Delays in construction projects are inevitable and, as a result, claims and disputes arise. Different causes of delay can come into play and therefore the need to identify and classify different causes of project delay arises. Different factors that contribute to project delay affect the likelihood of project delay in different degree of effectiveness. Fuzzy fault tree analysis (FTA) is suggested by this research to estimate the likelihood of project delay. Likelihood of delay membership function is further quantified using the weighted average defuzzification method. Two fuzzy logic models are implemented into the fuzzy FTA, using Visual Basic software: the models discussed in this research are Baldwin's rotational model and the Angular model. Comparison between the two fuzzy logic models has been carried out. Validation of the fuzzy FTA computer model is performed. Validation of the model was performed for adequacy and applicability of the model. On average, the validation performed by independent construction engineers and fuzzy logic experts produced satisfactory results. The computer software suggested by this study is an attempt to assess the likelihood of the project delay, which helps reduce delays in construction projects that can cause time loss.     

SMW工法支护结构失效概率的模糊事故树分析

针对常规事故树不能考虑基本事件发生概率的不确定性这一现状,通过引入模糊集的概念,将常规事故树中基本事件的发生概率模糊化,用三角形模糊数代替确定性发生概率,应用模糊数截集方法,推导了模糊事故树的相关算法。采用模糊事故树方法得到深基坑工程SMW工法支护结构的模糊失效概率,并进行了敏感性分析,找出对顶事件发生概率影响较大的基本事件,确认减小SMW工法支护结构发生事故的相关措施。与常规事故树方法比较表明,模糊事故树方法不仅能达到常规方法的分析目的,而且可以得到深基坑支护工程失效可能性的分布规律。     

Cost-effectiveness fuzzy analysis for an efficient reduction of uncertainty

Many planning and production processes are characterized by uncertain data and uncertain information. For realistic modeling of such processes these uncertainties have to be considered. The new approach presented in this paper takes epistemic uncertainty into account, for which fuzzy set theory is applicable. In some cases it is possible and useful to reduce epistemic uncertainty by additional monetary investments. It is postulated that uncertain forecast values, e.g. expected safety, quality, or the completion date of a structure, can be improved or scheduled more precisely by a higher investment. Aim of the presented cost-effectiveness fuzzy analysis is the evaluation of the effectiveness of monetary investments on the reduction of uncertainty of the analyzed forecast values.     

An approach for greenway suitability analysis

Greenway analysis is designed to identify and measure the suitability of potential sites for greenway development. This evaluation can be regarded as an extremely difficult task due, in part, to the large number of criteria and large volume of data that may be required for the determination. The purpose of this paper is to present an approach to greenway analysis that integrates suitability analysis with geographic information system (GIS) technology to identify suitable sites for greenway development in the town of Prescott Valley, AZ, USA. This approach identified five major steps involved in the greenway analysis, these include: identification of land-use functions, spatial data collection, development of weighting values, data integration and analysis using GIS, and output evaluation. Land-use function identification, and weighting values were developed from a wide range of resources including the Prescott Valley General Plan, surveys, expert opinion and published literature. Spatial data were obtained from federal, state, and local agencies. Where specific data were not available, these data were collected from the site using inventory techniques. Three land-use functions were identified for the Prescott Valley study area, wildlife habitat, recreation, and riparian corridor. For each of these functions, four or five primary factors were determined. Additionally, for each factor, a land capability rating was established. Results of the surveys indicated that normalized weightings for the functions were 1.0 for wildlife habitat, 0.862 for recreation, and 0.653 for riparian corridor. Rankings for the primary factors within the functions ranged from a high of 0.468 to a low of 0.049, with the sum of weighting values for all factors within a function equal to 1.0. Land capability values for attributes within factors were set as high, moderate, low, and no capability. All data were integrated into a vector-based GIS software and a total of 14 coverages were created, Spatial analysis was performed using an overlay technique combining all factors within a function, and then by combining all resulting factor outputs to produce an overall greenway suitability analysis. The final analysis was then evaluated by a panel of experts to determine its accuracy and potential for use in a greenway development plan.     

铁路并行既有铁路软土地基处理及安全性分析

主要从铁路并行既有铁路软土地基的物理特性等方面对铁路软土地基可能出现的几种安全隐患进行具体分析,并给出合理的解决措施。     

消防安全设计参数不确定性分析

在对建筑物消防安全设计参数进行分类的基础上,介绍这些参数的不确定性的处理方法。基于β可靠性指标法研究建筑物结构构件在设定火灾下的耐火性,用失效区失败的概率表征构件耐火的不确定性。结果表明,正确地处理消防安全设计参数的不确定性可以为消防工程师和建筑师进行建筑物消防安全设计和决策提供可靠的依据。     

Reliability evaluation in nonlinear analysis of reinforced concrete structures

Modern building codes provide a basis for development of advanced nonlinear models for analysis and design of reinforced concrete (RC) structures. Application of nonlinear models permits direct evaluation of reliability of the whole structure at the stage of a structural analysis. In this paper a probabilistic method for reliability evaluation of plane frame structures with respect to ultimate limit states is proposed. The method is based on a combination of the nonlinear finite element structural model and the first-order reliability method (FORM). Implementation of the FORM for nonlinear analysis of RC structures is considered. Uncertainties associated with the structural model are taken into account and their influence on structural reliability is examined via sensitivity analysis.     

Spatial and temporal analysis of urban flood risk assessment

Urban flood risk assessment requires quantification of uncertainty that is spatially and temporally variable. This paper presents a new approach to urban flood risk assessment by: (a) integrating objective and subjective uncertainties and (b) providing full insight into spatial and temporal change of flood risk. A 1-D storm sewer model and a 2-D surface flow model are integrated to describe the dynamic interactions between overland flow on the streets and flow through the storm sewer network. The fuzzy set theory approach is used to assess spatial and temporal variability of urban flood damage, and the acceptable level of partial flood damage. The spatial and temporal variability of fuzzy performance indices: (i) combined reliability-vulnerability; (ii) robustness and (iii) resiliency, are generated as the outcome of the urban flood risk analysis. The methodology is illustrated using the residential community of Cedar Hollow (London, Ontario, Canada) as a case study.     

Assessment of existing steel structures. A guideline for estimation of the remaining fatigue life

A new methodology, called moment matching, to efficiently estimate repair costs of a building due to future earthquake excitation is presented. As well as excitation uncertainties, other uncertainties considered include those in the structural model and those in the capacity to resist damage and the unit repair costs of structural and non-structural components. Given the first few moments of the basic uncertain variables, moment matching uses specially selected point estimates to propagate the uncertainties in order to more accurately estimate the first few moments of the repair costs. Two buildings are chosen as illustrative examples to demonstrate the use of moment matching: one hypothetical three-degree-of-freedom shear building, and a real seven-storey hotel building. It is shown that the moment matching technique is much more accurate than the First-Order Second-Moment approach when propagating the first two moments, whilst the computational cost is of the same order. The repair cost moments estimated by the moment matching technique are also compared to those obtained by the more computationally demanding Monte Carlo simulation, and it is concluded that as long as the order of the moment matching is sufficient, the comparison is satisfactory. Last, but not least, a procedure for sensitivity analysis is discussed and it is concluded that the most important uncertainties for the real building example are those that correspond to spectral acceleration, component capacity, ground motion details and unit repair costs.     

Fuzzy approach for optimum replacement time of mixed infrastructures

Investments in infrastructure assets represent a sizable portion in the governments’ public fund. Continuous maintenance, rehabilitation, and replacement are required to maintain the level of service of infrastructure assets. Knowing the replacement needs of infrastructures and the timing of replacement are challenging tasks. This paper presents a decision support tool that aids in deciding the best time to replace several types of infrastructure assets, that is, mixed infrastructure. The paper uses fuzzy logic to model uncertainties in order to identify the useful lifetime of each infrastructure asset. Infrastructure replacement decision is made based on least cost option(s). A fuzzy logic tool is applied in three steps: data fuzzification, fuzzy inference, and data defuzzification. The developments made in the fuzzy logic tool are presented. A numerical example is presented to demonstrate the practical features of the proposed tool.     

基于Info-Gap理论的地下结构稳健性分析方法

围绕基于Information-Gap(I-G)理论的地下结构稳健性方法展开研究。首先,根据地下结构输出响应模型中不确定参量可能的取值范围及不同波动幅度对结构安全性能的影响,采用I-G模型量化处理不确定参量;其次,通过地下结构失效准则确立输出模型响应值与临界值之间的关系,由此构建稳健函数,并将结构发生失效前能够容许的不确定参量之最大波动幅度值定义为稳健可靠性指标来度量地下结构的可靠程度,从而形成了基于I-G理论的地下结构稳健性分析方法。最后,以某隧道衬砌稳健性分析为例,详细展示了地下结构稳健性分析的具体实施流程。工程算例表明,稳健可靠性指标反映了结构性能主动抵抗不确定性参量变化的能力。稳健性方法为不易得到不确定性因素足够信息的地下结构可靠性分析开辟了一条新途径。     

Logical analysis of assumptions in fatigue design

Whatever method is used to estimate the safety of a structure under fatigue loading, there is inevitably a mismatch between the predictions of the theoretical model used and the performance of the actual structure when built. It is the purpose of this paper to present an analysis of this mismatch and to suggest a method of fuzzy logical analysis which may be used to assess it. Three types of parameters are identified. The first group are those which can be precisely defined, measured and controlled in a laboratory experiment; the second are those which are difficult to define and measure even in the laboratory and the third are those unknown parameters which account for the scatter in laboratory fatigue tests.

A fuzzy logic model of the mismatch between the behaviour of the completed structure and the laboratory models and between the service loading and those loadings used in the laboratory is presented. The probability of a particular class of weld detail in a bridge structure is calculated using a probabilistic measure on a fuzzy relation. This probability is then modified by the results obtained from subjective estimates input to the fuzzy logic model to obtain a fuzzy probabilistic measure of the safety of the detail.     

基于SPA-TFN-SS耦合的隧道瓦斯突出分析模型

瓦斯突出受诸多不确定性因素影响与控制,其预报是一个复杂的不确定性系统问题。本文应用集对分析理论的多元联系数表达式来定量描述瓦斯突出评价指标样本与评价标准等级之间隶属关系的层次性和模糊性,并用三角模糊数定量表示联系数的差异度系数的连续变化过程,进而通过随机模拟实现把三角模糊数及其函数之间的运算转化为普通实数之间的运算,结合各个评价指标的权重,综合对隧道瓦斯突出进行分析。实例应用表明:该模型应用与隧道瓦斯突出评价是有效可行的,且能提供评价结果的可靠性分析信息。     

施工期钢筋混凝土结构安全分析的探讨

结构在施工过程中的平均风险率远高于使用期,对施工期钢筋混凝土结构进行安全分析与控制,就必须对施工期间荷载在部分完成的结构和支撑系统之间的传递进行分析与研究。本文通过具体的工程案例比较发现：现行的钢筋混凝土结构设计规范和施工规范不能对施工期钢筋混凝土结构的受力进行合理分析,因而无法对施工期结构的安全进行有效的控制。国内目前推广应用的部分施工期结构安全计算软件尚不能很好地对施工期钢筋混凝土结构进行受力分析,而清华大学土木工程系与北京第七建筑工程公司合作开发出一套人机交互的“施工期钢筋混凝土结构安全分析与控制软件-SAC”,能对施工期整个阶段每次施工步骤对各楼层受力的影响进行分析,具有一定的科学性。     

围岩稳定性集对分析–可变模糊集综合评价模型

围岩稳定性评价是一个复杂不确定系统问题。应用集对分析和可变模糊集合理论,建立了围岩稳定性评价的集对分析–可变模糊集综合评价模型,简化了构建相对差异度过程,提高了评价结果的准确性和可靠性,并应用于实际工程,与其它分类方法进行了对比分析,结果表明该法是有效可行的,且更客观。     

熵权–集对分析模型探测堤坝渗漏

堤坝渗漏过程中水流携带的各种物质构成“信息流”,通过“信息流”中的“信息熵”可以确定地下流场的性质,其中运用水化学和环境同位素方法探测堤坝渗漏已经得到广泛应用。基于信息熵和集对分析系统理论,并结合水化学和环境同位素探测方法,建立了一种新的堤坝集中渗漏通道探测模型：熵权—集对分析模型。将PH,电导,Cl,δD和δO作为探测指标,依据探测指标和判断标准界限值的关系,对待测样本进行同一、差异和对立的集对分析,计算各探测指标联系度; 采用基于极大熵原理的熵权赋值法确定不同指标的权重,计算各样本综合联系度; 并据此将待测样本分类,进而确定钻孔内水的来源。最后将该模型应用于探测南方某水库堤坝渗漏问题,并利用流速和温度探测方法相互验证,分析表明：该模型探测结果跟流速和温度探测结果相吻合。