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.     

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.     

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.     

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.     

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。     

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。     

结构设计的不确定问题分析及在既有结构工程评定中的利用

在工程评定中应该对结构设计阶段的不确定性储备合理利用,以减少加固工程量。从分项系数设计方法、材料强度、计算模型、统计参数的变异性以及作用五个方面,对结构设计阶段的不确定问题进行分析,提出对既有结构工程评定中合理利用这些储备的原则。最后以一实际工程为例,在对结构构件承载力评定时考虑材料强度的不确定性储备。检测评定结果表明,构件承载力的安全水平均高于设计要求值,该混凝土结构安全可靠。     

基于集对分析的供水管网漏损预测模型

探讨了集对分析法在供水管网漏损预测中的实现途径,从同、异、反三个方面度量漏损预测样本与历史样本的相似性,建立了基于集对分析的漏损预测( SPA - LF)模型.应用结果表明,SPA - LF对预测过程不确定性的描述较为详细,供水管网漏点数及漏损频率预测结果均显示出SPA - LF模型的有效性,减小了预测过程的不确定性,与灰色系统模型、指数平滑模型及神经网络模型预测结果相比,SPA - LF模型取得了满意的预测精度.SPA - LF模型计算简单,使用方便,可为供水管网的维护及管道更新提供决策支持.     

Bayesian analysis of uncertainty for structural engineering applications

There has been recent interest in differentiating aleatory and epistemic uncertainties within the structural engineering context. Aleatory uncertainty, which is related to the inherent physical randomness of a system, has substantially different effects on the analysis and design of structures as compared with epistemic uncertainty, which is knowledge based. Bayesian techniques provide powerful tools for integrating, in a rigorous manner, the two types of uncertainties. In a purely probabilistic viewpoint, the uncertainties merge, resulting in widened probability densities. From the viewpoint of design or experimentation, however, the two types of uncertainties have widely different effects. The purpose of this paper is to develop insight into these effects, using Bayesian-based analytical expressions for the aleatory and epistemic uncertainties. The paper goes beyond standard Bayesian conjugate distributions by incorporating the effects of model uncertainty, where the applicability of two or more analytical models are used to describe the structure of interest. The influence of multiple model uncertainties is explored for two problems: the Bayesian updating process as data is acquired, and the design of simple parallel systems.     

Cost-benefit analysis of seismic-isolated structures with viscous damper based on loss estimation

This paper presents a methodology to utilise performance-based seismic design procedure for evaluating isolated structures with or without viscous dampers (VD) considering cost-benefit analysis. A non-linear four-story archetype of conventional steel structure, a lead-rubber-bearing isolated structure and a natural rubber-bearing isolated structure with the linear VD are compared with each other under far-field (FF) and near-field (NF) ground motions. Also, loss parameters, such as expected annualised loss, expected annualised repair time, expected annualised fatalities and expected annualised injuries based on loss estimation process, are utilised for evaluating the structures. Sensitivity analysis is used to study the effect of modelling uncertainty variations in the loss estimation process. It has been found that the effectivity of supplemental damping for low damping isolated structures increases in the NF comparing with the FF ground motions. Finally, the cost-benefit analysis is done to calculate payback period of investment for additional cost of the isolation system with or without the supplemental damping. The advantage of loss estimation is an improved method to evaluate the effectiveness of the isolation system in terms of loss parameters that are useful in the cost-benefit studies and for determining rational insurance premiums.     

Risk analysis in construction: a paradigm shift from a hard to soft approach

Risk analysis in construction is becoming more popular as competition, project size and complexity increase. Traditional risk analysis relies on rules of thumb. While this approach can work, it is neither robust nor reliable. The development of information technology has made the use of probabilistic estimating and simulation a practicable alternative. These techniques are, however, precise but not necessarily accurate as simplification and many assumptions are used. Further information technology development in expert systems and the paradigm shift in systems engineering from a hard to soft approach has promoted an alternative approach to risk analysis utilizing the theory of fuzzy sets which translates linguistic expressions (such as highly likely) into numerical membership functions. This paper introduces risk analysis in construction against characteristics of the industry. It is argued that normative theories in probability are not as applicable in the construction industry as first perceived. The concept of fuzzy sets is described and the difference in approach in modelling risk between probabilistic and fuzzy methods will be presented. Initial empirical study reveals the applicability of fuzzy sets theory in risk analysis. This is important in that a model of risk analysis can be developed requiring the user to express risk attitude linguistically. Moreover, the results are also in linguistic terms and can, therefore, be understood and interpreted correctly by the user.     

谈某厂房现有结构鉴定分析

以某车间为例,利用MIDAS Gen和PKPM结构计算分析软件分别对该厂房拱桁架结构和整体结构进行了受力分析,并进行了鉴定,可为类似的工业厂房结构受力和鉴定分析提供参考。     

基于熵权集对分析与可变模糊集的水源地水质评价

通过运用集对分析法、熵值原理和可变模糊集,构建了水质评价新模型.该模型利用可变模糊集的思想,将熵值集对分析法得出的加权平均联系度作为相对差异度,计算水质的最终评价等级.采用该方法对2011年我国北方某市5个监测断面的6项水质指标进行了综合评价.结果表明,该水源地整体水质较好,4个监测断面属于Ⅲ类水体,1个检测断面属于Ⅱ类水体.与其他常规方法比较,该模型评价结果合理,计算简便.     

Life quality index for the estimation of societal willingness-to-pay for safety

The engineering and management of human safety is an important societal objective that includes extensive efforts by governments, both legislative and administrative, to enhance the health and safety of the public. Although the achievement of safety goals depend primarily on individuals and organizations responsible for safety, much support is drawn from expertise in diverse scientific and engineering disciplines. The activities range from structural safety (dams, tunnels, bridges to tall buildings) to safe operation of hazardous industrial installations (energy generation facilities, LNG terminals, petrochemical plants) to transportation systems (airline, rail, car safety) to technologies designed to minimize adverse impacts on the environment. All these activities are crucially concerned with risk: with the likelihood and the probable effects of various measures on life and health. We have developed a unified rationale and a clear basis for effective strategic management of risk across diverse sectors. Safety is an important objective in society but it is not the only one. The allocation of society's resources devoted to safety must be continually appraised in light of competing needs, because there is a limit on the resources that can be expended to extend life. The paper presents the Life Quality Index (LQI) as a tool for the assessment of risk reduction initiatives that would support the public interest and enhance safety and quality of life. The paper provides an intuitive reformulation of the LQI as equivalent to a valid utility function that is consistent with the principles of rational decision analysis. The LQI is further refined to consider the issues of discounting of life years, competing background risks, and population age and mortality distribution. The LQI is applied to quantify the societal willingness-to-pay, which is an acceptable level of public expenditure in exchange for a reduction in the risk of death that results in improved life-quality.