Integration of structural health monitoring in a system performance based life-cycle bridge management framework

In this paper, an approach for integrating the information obtained from structural health monitoring in a life-cycle bridge management framework is proposed. The framework is developed on the basis of life-cycle system performance concepts that are also presented in this paper. The performance of the bridge is quantified by incorporating prior knowledge and information obtained from structural health monitoring using Bayesian updating concepts. This performance is predicted in the future using extreme value statistics. Advanced modelling tools and techniques are used for the lifetime reliability computations, including incremental nonlinear finite element analyses, quadratic response surface modelling using design of experiments concepts, and Latin hypercube sampling, among other techniques. The methodology is illustrated on an existing bridge in the state of Wisconsin.     

On the accuracy of diffusion models for life-cycle assessment of concrete structures

In durability analysis and life-cycle assessment of concrete structures transport of chlorides and other aggressive agents is generally described by using Fick’s laws of diffusion. This model is frequently applied in a simplified one-dimensional (1D) form. However, in practical applications the diffusion process is more properly described by two- or three-dimensional patterns of concentration gradients. In this paper, the accuracy of the 1D modelling of diffusion and its impact on the life-cycle assessment of concrete structures under corrosion is evaluated in deterministic and probabilistic terms with respect to more accurate two-dimensional (2D) formulations. The influence of the diffusion modelling on the time-variant corrosion damage of concrete cross-sections is studied with reference to the local damage of the reinforcing steel bars and the global deterioration of bending moment–curvature capacity curves. The results show that 2D diffusion models may be necessary for a realistic life-cycle assessment of concrete structures under corrosion, since 1D models can lead to significant inaccuracies depending on the geometrical aspect ratio of the cross-section, location of reinforcing steel bars and exposure conditions.     

高性能结构抗多次多种灾害全寿命性能分析与设计理论研究进展

为促进高性能结构抗多次多种灾害全寿命性能设计理论研究在我国的发展,详细介绍了该领域的国内外研究现状并建立了其基本研究框架。对高性能结构在全寿命周期内可能遭受的多种灾害单独作用和联合作用的发生概率模型的研究成果进行了阐述,以碳化腐蚀作用和风致疲劳作用为例,论述了在结构全寿命周期内由环境作用引起材料及构件退化的时变模型研究现状,为开展多次多种灾害作用下高性能结构的全寿命性能分析研究提供了方向,并系统介绍了多种灾害作用下结构易损性分析方法和考虑灾害损失成本的结构全寿命抗灾性能优化设计方法的研究进展。基于全寿命周期的结构抗多次多种灾害性能设计方法,能够合理地解决传统设计方法中未考虑多种灾害联合作用和结构性能退化问题,对于建筑结构设计领域的发展具有重要意义。     

基于全寿命周期费用控制的沥青路面设计管理

介绍了沥青路面设计中引入全寿命周期费用控制设计理念的意义,阐述了沥青路面设计实施全寿命周期费用控制的设计要点,最后指出设计院在LCC管理中的地位和作用,说明了运用全寿命周期费用的理念来进行沥青路面设计方案的比选和决策是科学而合理的。     

网壳结构寿命周期总费用的计算方法研究

现代结构系统在灾害中产生巨大经济损失的特点,使人们意识到在结构设计之初就对结构的寿命周期总费用进行有效评估、并反过来指导工程设计具有重要意义。对网壳结构寿命周期总费用的计算方法进行研究,分别提出初始造价、维护费用和失效损失的计算公式,并考虑寿命周期内网壳结构可能受到的荷载发生的概率,建立寿命周期总费用的计算方法,编制网壳结构寿命周期总费用的计算程序。通过一具体的网壳结构工程算例验证上述方法和程序的有效性。研究结果表明,网壳结构初始造价的追加投资会由于结构使用过程中失效损失费用的减小而得到补偿,而寿命周期总费用最小正是结构设计的最优状态,按照现行规范设计方法得到的结构配置方案不一定是寿命周期总费用最小的方案。     

The development of life-cycle costing for buildings

The history of the application of life-cycle costing (LCC) began in the UK in the late 1950s and, until now, the state of its development as a concept is not clear. A literature review is presented that shows the changing approaches to LCC by drawing on four major academic journals and 45 peer-reviewed papers. The review verifies that there is a revival of interest in using LCC in tandem with other life-cycle methodologies for research on sustainable building. It also presents a set of methods that are applicable to model and estimate the life-cycle costs of ‘conventional’ and ‘green’ buildings with the objective of distinguishing them. Through the information gathered, it provides a centralized source of reference for the assumptions used in LCC calculations concerning some key input parameters. The finding shows an increasing trend of publications on the evaluation of economic options for green building designs and performance. The directions are clear that the concepts and methods have to evolve to a state where they will help to integrate and optimize economic, social and environmental considerations to deliver more sustainable built environments in the future.     

Extension of dynamic programming models for management optimisation from single structure to multi-structures level

The aim of this article is the management optimisation (inspection, maintenance and rehabilitation (IM&R)) of a group of structures. It is supposed that the optimisation is constrained by limited available budget at the beginning of each time period during the entire time horizon thus creating an economical dependence between the decisions related to each of the structures. A Lagrangian relaxation technique is used for the extension of existing dynamic programming methods from single structure to multi-structures level. The methodology is illustrated by using a Generalised Partially Observable Markov Decision Process having a decision tree composed of a sequence of two decisions at the beginning of each time period, namely an inspection decision followed by a maintenance action decision. A numerical example concerning the optimisation of IM&R of 16 different bridges is presented.     

Investment priorities for the management of hydraulic structures

Maintenance management of the hydraulic structures requires the selection of the most necessary maintenance intervention to ensure their proper operation and structural safety. Given the characteristics of these structures, many types of damage may appear, so it is not easy to take a decision. The purpose of this paper is to present the Prioritisation Index for the Management of Hydraulic Structures (PIMHS), a multi-criteria decision-making system based on the three axioms of sustainability (social, environmental and economic), which orders and prioritises non-similar maintenance investments in hydraulic structures. The results obtained show that PIMHS can be used by decision-makers to prioritise, in hydraulic structures, all kinds of maintenance interventions where the damages cannot lead to dam break.     

A model for earthquake risk management based on the life-cycle performance of structures

Over 50 years of design life, buildings are exposed to different magnitudes and frequencies of earthquakes that require consideration of life-cycle cost (LCC). The LCC entails quantifying the building performance under seismic hazard and investments throughout the life of the structures. Traditional LCC utilises probabilities of being in different damage states. However, for buildings with inherent irregularities (e.g. vertical irregularity and plan irregularity), these probabilities are not readily available. In this paper, a system-based approach, utilising fuzzy set theory, is used to quantify the possibility of being in different damage states. The analysis is limited to study the effect of seismic exposure on the building LCC. The proposed method is illustrated with two case studies, a six-storey reinforced concrete (RC) building located in Vancouver, Canada, and vulnerability of an urban centre with 1000 RC buildings. Furthermore, sensitivity analysis is carried out to highlight the impact of different building performance modifiers on the LCC.     

Fatigue and fracture simulation of welded bridge details through a bi-linear crack growth law

This paper deals with the application of a probabilistic fracture mechanics approach to predict the fatigue life of welded steel details in the presence of cracks under bridge spectrum loading. It is based on a recently proposed bi-linear relationship to model fatigue crack growth and incorporates a failure criterion to describe the interaction between fracture and plastic collapse. The formulation leading to the expected number of cycles to failure is first outlined, followed by a simple example on a butt-welded detail. Uncertainty modelling, especially on fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using simulation with Latin Hypercube Sampling, and emphasis is placed on a comparison between linear and bi-linear crack growth models. The latter is found to lead to higher fatigue life estimates and significantly different crack size distributions, both of which have implications on inspection schemes for steel bridge components.     

The use of stress-density functions for lifetime predictions of brittle structures

The tools necessary to perform a lifetime analysis for a brittle structure are presented. The paper explains methods for measuring the relevant material properties, such as Weibull modulus m, normalization strength σ₀, and subcritical crack growth parameter n, and for combining them with suitable statistics, stress analysis, and linear-elastic fracture mechanics, in order to arrive at strength-probability-time (SPT) diagrams for a particular structure. Moreover, it will be shown, how mathematical difficulties arising during the statistical analysis can be overcome by making use of the so-called stress-density functions, which were recently introduced by Nadler [1].     

Fatigue reliability of welded steel structures

In general, two different approaches to the formulation of the fatigue limit state are considered, the first based on S-N lines in combination with Miner’s damage accumulation rule, and the second based on fracture mechanics crack growth models and failure criteria. Often, the two approaches are used sequentially, with S-N being used at the design or preliminary assessment stage and fracture mechanics for more refined remaining life or inspection and repair estimates. However, it is essential to link the results, and the decisions made, at the design and assessment stages, and it is therefore important to develop compatible methodologies for using these two approaches in tandem. In doing so, it is essential to understand and quantify different uncertainty sources and how they might affect the robustness of the results obtained, and the subsequent decisions made about the structure. The objective of this paper is to highlight parts of recent research at the University of Surrey on the fatigue assessment of steel bridges. The work includes the development of a probabilistic fracture mechanics methodology for the prediction of fatigue reliability, using up-to-date crack growth and fracture assessment criteria and incorporating information on inspection and subsequent management actions.     

Computational platform for the integrated life-cycle management of highway bridges

Throughout their service life, highway bridges are subject to progressive deterioration in performance; an issue that may render the use of these facilities unsafe at some point in time. Over the last few decades, there has been successful research towards developing procedures for establishing the various vital elements required in the life-cycle management of civil infrastructure. It is noted, however, that frameworks for integrating these elements together are lacking. The objective of this paper is to present an integrated framework for the life-cycle management of highway bridges in the form of a detailed computational platform. The elements integrated into the framework include the advanced assessment of life-cycle performance, analysis of system and component performance interaction, advanced maintenance optimization, and updating the life-cycle performance by information obtained from structural health monitoring and controlled testing.     

工程结构可持续性设计理论架构

工程结构设计以安全和可靠性为基本属性,在人本化关切层面不断进步,但对工程结构造成环境影响的忽视致使工程建设热潮成为环境退化诱因之一。近年兴起的生命周期评价研究致力改善这一现状,依此可建立工程结构的环境可适应性设计,实现生命周期环境影响调控,引导环境友好的工程进步。然而长期以来,工程结构设计与环境影响设计的研究进展处于两条近乎平行的轨道,两类单向设计在实践中常相互制约。工程结构与环境系统的同步可持续是土木工程可持续发展的必然要求,因而亟需构建结构与环境相容共生理论体系。基于此,提出可持续性作为结构设计的控制属性,给出可靠性满足的前提下,工程结构对环境影响在环境系统中的可承受程度。通过建立基本耦合关系和动态相容耦合关系,关联可靠性与可适应性,反映结构-环境共生体的动态反馈影响机制,构建双向设计的基本路径。进一步,定义碳强度和碳容度,提出可持续性目标选取与简化实现建议,列出多层次操作要点,为绿色建造提供理论基础。     

Investigation of fatigue resistance of fillet-welded tube connection details for sign support structures

Stiffened and unstiffened fillet-welded tube-to-transverse plate connection details are widely used for mast-arm and base-plate connections for highway sign structures. However, due to repetitive wind loads, cyclic fatigue stresses are induced and they are the primary source of failure in welded connections at these locations. The resistance of fatigue critical details has been an on-going research topic because of limited experimental results and the variability in existing fatigue testing results. The main objective of this study is to evaluate fatigue resistance of fillet-welded tube connection details by utilizing the advanced fatigue tool in ANSYS Workbench platform. Finite Element (FE) models development and model validation using existing test data was presented. The resulting fatigue resistance from FE analysis was expressed in terms of fatigue life, fatigue damage, and fatigue safety factor to determine the fatigue performance of fillet-welded connections. Existing fatigue test data was grouped to perform a synthetic analysis and then analysis results were provided to determine input data and fatigue limit for the fatigue module. The local stress level at fatigue critical locations was evaluated using a static FE model for different number of stiffeners and boundary conditions. The results of this investigation provides fatigue resistance of fillet-welded connection details in the form of fatigue life, fatigue damage and safety factor for various connection parameters and structural conditions.     

混凝土结构设计原理教学细节探讨

混凝土结构设计原理课程是土木工程专业必修的一门专业基础课,在课程体系中居于重要地位。文章从课程的特点及实际课堂教学经验出发,梳理和剖析教学中需要注意的若干细节问题,旨在带动学生的学习热情,确保课堂教学质量与效果,提高学生的专业素养,为其进一步的学习和工作奠定基础。     

高速公路网全天候安全运营控制管理系统研究

从国外高等级公路运输网安全管理现状出发,探讨了高速公路管理系统的构成及功能,阐述了路网研究应考虑的因素,并对基于全天候路网运营安全管理对策及决策展开论述,以期改善目前公路运输网安全运营状况。     

A Bayesian network framework for statistical characterisation of model parameters from accelerated tests: application to chloride ingress into concrete

This paper addresses the topic of long-term characterisation and probabilistic modelling of chloride ingress into reinforced concrete (RC) structures. Since the corrosion initiation stage may cover various decades, normal tests which simulate chloride penetration into concrete in laboratory conditions as the same as natural conditions, will require significant experimental times. Hence, long-term lifetime assessment of RC structures under chloride attack remains still a challenge. In practice, this problem is solved through the use of accelerated tests which speed up the chloride ingress rate and provide valuable mid- and long-term information on the chloride penetration process. Nevertheless, this information cannot be directly used for parameter statistical characterisation if the equivalent times required in natural conditions to reach the same chloride concentrations in the accelerated tests are unknown. Consequently, this study proposes a novel iterative approach based on Bayesian network updating to estimate chloride ingress model parameters from the data obtained under accelerated laboratory conditions. The Bayesian network structure and iterative approach are first tested with numerical evidences. Thereafter, the complete proposed methodology is verified with results from real experimental measurements. The results indicate that combining data from normal and accelerated tests significantly reduces the statistical characterisation error of model parameters.     

Improved strategies and optimization of calibration models for real-time PCR absolute quantification

Real-time PCR absolute quantification applications are becoming more common in the recreational and drinking water quality industries. Many methods rely on the use of standard curves to make estimates of DNA target concentrations in unknown samples. Traditional absolute quantification approaches dictate that a standard curve must accompany each experimental run. However, the generation of a standard curve for each qPCR experiment set-up can be expensive and time consuming, especially for studies with large numbers of unknown samples. As a result, many researchers have adopted a master calibration strategy where a single curve is derived from DNA standard measurements generated from multiple instrument runs. However, a master curve can inflate uncertainty associated with intercept and slope parameters and decrease the accuracy of unknown sample DNA target concentration estimates. Here we report two alternative strategies termed ‘pooled’ and ‘mixed’ for the generation of calibration equations from absolute standard curves which can help reduce the cost and time of laboratory testing, as well as the uncertainty in calibration model parameter estimates. In this study, four different strategies for generating calibration models were compared based on a series of repeated experiments for two different qPCR assays using a Monte Carlo Markov Chain method. The hierarchical Bayesian approach allowed for the comparison of uncertainty in intercept and slope model parameters and the optimization of experiment design. Data suggests that the ‘pooled’ model can reduce uncertainty in both slope and intercept parameter estimates compared to the traditional single curve approach. In addition, the ‘mixed’ model achieved uncertainty estimates similar to the ‘single’ model while increasing the number of available reaction wells per instrument run.