Modeling of risk-based inspection,maintenance and life-cycle cost with partially observable Markov decision processes

The utilization of Markov decision processes as a sequential decision algorithm in the management actions of infrastructure (inspection, maintenance and repair) is discussed. The realistic issue of partial information from inspection is described, and the classic approach of partially observable Markov decision processes is then introduced. The use of this approach to determine optimal inspection strategies is described, as well as the role of deterioration and maintenance for steel structures. Discrete structural shapes and maintenance actions provide a tractable approach. In-service inspection incorporates Bayesian updating and leads to optimal operation and initial design. Finally, the concept of management policy is described with strategy vectors.     

A model for predicting plant maintenance costs

A model is presented that predicts the total cost of plant maintenance (i.e. direct cost of maintenance plus indirect cost of lost production) and is derived studying a random sample of tracked hydraulic excavators. Analysis is based on the machine history file data of 33 plant items, modelled using multiple regression (MR) analysis. Validation of the model was determined via the combination of an observed high R 2 at 0.94 and various statistical tests which confirmed the prerequisites of a rigorous MR analysis. Machine weight, type of industry and company attitude towards predictive maintenance were found to be the best predictor variables of total plant maintenance cost. The paper also discusses reasons underlying the inclusion of predictor variables in the final model, and concludes with clear directions for future research in this field.     

Design and maintenance programme optimization for large infrastructure systems

The design, construction and operation of civil infrastructure systems in modern society has become a critical issue worldwide. These processes cannot be restricted to solving just the mechanical problem. On the contrary, they should be designed within a framework that considers their life cycle, taking into account all costs in which the owner (or operator) will incur during the lifetime of the structure, and the benefits derived from its existence. This paper presents a strategy for optimizing the maintenance of technical facilities based on their life cycle within which deterioration and sudden failure due to extreme events may occur. A renewal model for the sequence of structural failures is used to define the objective function. The proposed model is useful for defining both an optimal maintenance policy (number of interventions and the time between them) and the design parameters. It can also be used for investment, planning and operation of new and existing facilities. The results have shown that a rational programme for maintenance and structural updating is essential for defining the efficiency of the investment in infrastructure projects.     

Deterioration patterns of building cladding components for maintenance management

Increasing demands are made on maintenance programmes to provide tools that will support maintenance planning. Among of the most important parameters affecting the efficiency of maintenance management are the precision and the reliability of the predicted service life (PSL) of building components. The main objective of this study was to develop a methodology for the establishment of databases listing deterioration patterns of building components based upon their actual condition. The methodology consists of four steps: (1) identification of failure patterns, (2) determination of the component performance (CP), (3) determination of the life expectancy of deterioration path (LEDP) and (4) evaluation of the predicted service life (PSL). The proposed methodology can be used for planning of maintenance activities, for evaluation of economic implications caused by intensive decay and for maintenance management.     

Optimal strategy for inspection and repair of structural systems

A new strategy for inspection and repair of structural elements and systems is presented. The total cost of inspection and repair is minimized with the constraints that the reliability of elements and/or of the structural system are acceptable. The design variables are the time intervals between inspections and the quality of the inspections. Numerical examples are presented to illustrate the performance of the strategy. The strategy can be used for any engineering system where inspection and repair are required.     

A multiple criteria evaluation of multi-family apartment block's maintenance contractors: I—Model for maintenance contractor evaluation and the determination of its selection criteria

The paper presents a model that describes the process of selecting dwelling maintenance contractors. The model is based on a multi-criteria evaluation of maintenance contractors, the determination of their utility level for the building's users and a bid price in negotiations that are made according to the results of the multiple criteria analysis. The proposed model could further be applied to plan dwelling maintenance operations. The criteria of maintenance contractor evaluation are selected by taking into consideration the interests and goals of the building's users as well as factors that influence the process of maintenance's efficiency. The correlation of the criteria characterizing maintenance contractors from various perspectives was determined.     

Allocation of effective maintenance limit for railway track geometry

Abstract

The objective of this study has been to develop an approach to the allocation of an effective maintenance limit for track geometry maintenance that leads to a minimisation of the total annual maintenance cost. A cost model was developed by considering the cost associated with inspection, preventive maintenance, normal corrective maintenance and emergency corrective maintenance. The standard deviation and extreme values of isolated defects of the longitudinal level were used as quality indicators for preventive and corrective maintenance activities. The Monte Carlo technique was used to simulate the track geometry behaviour under different maintenance limit scenarios and the effective limit was determined which minimises the total maintenance cost. The applicability of the model was tested in a case study on the Main Western Line in Sweden. Finally, a sensitivity analysis was carried out on the inspection intervals, the emergency corrective maintenance cost and the maintenance response time. The results show that there is an optimal region for selecting an effective limit. However, by considering the safety aspects in track geometry maintenance planning, it is suggested that the lower bound of the optimal region should be selected.     

The application of the risk management process in capital investment decisions for EHV transmission line projects

This paper reviews the viability of applying a risk management process to enhance capital investment decisions, when planning the construction of an extra-high voltage (EHV) overhead transmission line project that could be designed and built in the next 10 years by China Light & Power Company Limited, Hong Kong. Different project proposals will be considered for this transmission line as well as different completion dates. Each scenario will be investigated to determine the rate of return and expected cost to customer, using the net present value model. The lowest ‘cost to customer’ approach would be the normal criterion for project selection, assuming all proposals are technically viable and compatible with Hong Kong Government infrastructure plans.     

An augmented Lagrangian decomposition approach for infrastructure maintenance and rehabilitation decisions under budget uncertainty

This article addresses a general class of infrastructure management problems raised in maintenance and rehabilitation scheduling. Infrastructure agencies usually face budget uncertainties that eventually lead to suboptimal scheduling planning if maintenance decisions are made without taking the uncertainty into consideration. It is important for decision makers to adopt maintenance and rehabilitation scheduling policies that consider all budget scenarios. The authors propose a multistage, stochastic programming model to address this problem. The authors also develop a solution procedure using the augmented Lagrangian decomposition algorithm. A case study exploring the computational characteristics of the proposed algorithm is conducted and the benefit ofusing the stochastic programming approach is discussed.     

Indicators for inspection and maintenance planning of concrete structures

Based on an idea introduced by Benjamin and Cornell (1970. Probability, statistics and decision for civil engineers. New York: McGaw Hill) and previous works by the authors it is demonstrated how condition indicators may be formulated for the general purpose of quality control and for assessment and inspection planning in particular. The formulation facilitates quality control based on sampling of indirect information about the condition of the considered components. This allows for a Bayesian formulation of the indicators whereby the experience and expertise of the inspection personnel may be fully utilized and consistently updated as frequentistic information is collected. The approach is illustrated on an example considering a concrete structure subject to corrosion. It is shown how half-cell potential measurements may be utilized to update the probability of excessive repair after 50 years. Furthermore in the same example it is shown how the concept of condition indicators might be applied to develop a cost optimal maintenance strategy composed of preventive and corrective repair measures.     

Application of the principles of ILS to the development of cost effective maintenance strategies for existing building stock

Total spending on building maintenance in the UK has increased by 66% in the last 10 years (BMI, 1996). Total expenditure on maintenance in 1997 was £39.8 billion (BMI, 1998). Any significant reduction in building maintenance costs will therefore have a real impact on the national economy. This paper reports the results of a research project supported by the EPSRC at the University of Dundee, which sought to quantify the benefits of applying integrated logistics support (ILS) to the development of cost-effective maintenance strategies for existing building stock. ILS is a managerial and technical approach that ensures that the client/user will receive a building that will meet performance requirements (durability, reliability, maintainability, performance, etc.) at the lowest whole life cost. The principles of ILS are described and a systematic framework for selecting the most appropriate and cost-effective maintenance task for each individual element in a building is developed. The decision logic processes for identifying each failure consequence and for selecting the most applicable and cost-effective maintenance task are derived. The maintenance cost savings arising from the application of two ILS techniques - failure modes and effects analysis, and reliability centred maintenance - to a sample of 18 properties were calculated to be 18.5%.     

Optimal maintenance strategies for bridge networks using the supply and demand approach

This paper presents a probability-based approach for optimising the management of bridge networks. Most of the Bridge Management Systems are focused on condition features to ensure a minimum safety level for each individual bridge. Their location on the road network, the consequences of inadequate service due to maintenance actions are therefore not taken into consideration. These multiple criteria should be considered when scheduling maintenance activities. To overcome these limitations, a probabilistic supply and demand strategy is proposed for determining the optimal maintenance planning for each interconnected bridge. The problem is solved with genetic algorithms. One objective function is first introduced, corresponding to the summation of all the maintenance, failure, and user costs. Then, two conflicting objective functions are considered, the total user costs and the maintenance and rehabilitation costs. Safety and serviceability aspects are taken into account in the methodology and the theoretical and numerical developments are applied on a part of the French national network.     

MEMRRES: model for evaluating maintenance,repair and rehabilitation strategies in concrete bridge decks

It is very important for State Departments of Transportation (DOT) to establish strategies with regard to maintenance, repair, and rehabilitation (MR&R) of bridges. With the availability of Bridge Management Systems (BMS) such as PONTIS and BRIDGIT, owners are beginning to emphasize cost-effective proactive strategies from the start, when the bridge is new. Therefore, a model is required for the development of optimal MR&R action scenarios suitable to each DOT for effective management of the bridges. This article introduces a Model for Evaluating Maintenance, Repair and REhabilitation Strategies (MEMRRES) in concrete bridge decks. The MEMRRES assists the decision makers in determining the optimal MR&R strategy among the feasible MR&R strategies. The MEMRRES methodology is explained through a hypothetical example and is applied for determining the optimal MR&R strategy of concrete bridge decks for 24 State DOT (DOTs). It can be used as a tool by bridge engineers within their respective DOT to select cost-effective MR&R actions for concrete bridge decks.     

Reliability-based temporal and spatial maintenance strategy for integrity management of corroded underground pipelines

In this work, a novel stochastic model framework for predicting the external corrosion growth in buried pipeline structures has been developed, and a reliability-based temporal and spatial maintenance strategy is presented. The spatial correlation of soil properties is modelled via hidden Markov random field. The temporal correlation of the corrosion rate is characterised by the geometric Brownian bridge process. A Bayesian inferential framework is employed to estimate the model parameters of the corrosion growth model using in-line inspection data. The proposed corrosion growth model was validated with actual inspection data. In the reliability analysis, the impact of device detectability is considered and hence the estimated failure probability is more realistic. The proposed maintenance strategy is directly based on the time-specific and location-specific failure probability. The application of the proposed model and maintenance strategy is illustrated through a real-life pipeline system. The results indicate that the proposed maintenance strategy is an adaptive and dynamic scheme that is able to improve the efficiency of inspections.     

多支点支护结构优化设计

本文将地层损失法和杆系有限元增量法弹塑性分析相结合 ,协调支护结构内力与变形计算。对多支点支护结构 ,通过变形曲线面积积分建立了比较系统的多目标优化模型 ,并运用复合形法实现优化计算 ,求出满足目标要求的最优开挖与支撑工艺。文中两个典型实例有力地体现了该模型的技术经济意义。     

Computational framework for risk-based planning of inspections,maintenance and condition monitoring using discrete Bayesian networks

This paper presents a computational framework for risk-based planning of inspections and repairs for deteriorating components. Two distinct types of decision rules are used to model decisions: simple decision rules that depend on constants or observed variables (e.g. inspection outcome), and advanced decision rules that depend on variables found using Bayesian updating (e.g. probability of failure). Two decision models are developed, both relying on dynamic Bayesian networks (dBNs) for deterioration modelling. For simple decision rules, dBNs are used directly for exact assessment of total expected life-cycle costs. For advanced decision rules, simulations are performed to estimate the expected costs, and dBNs are used within the simulations for decision-making. Information from inspections and condition monitoring are included if available. An example in the paper demonstrates the framework and the implemented strategies and decision rules, including various types of condition-based maintenance. The strategies using advanced decision rules lead to reduced costs compared to the simple decision rules when condition monitoring is applied, and the value of condition monitoring is estimated by comparing the lowest costs obtained with and without condition monitoring.     

Development of a bridge maintenance system for prestressed concrete bridges using 3D digital twin model

Abstract

Preventive maintenance is increasingly becoming an essential strategy in the bridge industry owing to its proactive advantage of maintaining the structural sustainability during its entire service life. Several in-use bridges lack an appropriate regular maintenance solution, leading to extra cost during the operation stage. This paper proposes a new generation of the bridge maintenance system by using a digital twin model concept for more reliable decision-making. A detailed solution is proposed in this work to enhance the bridge maintenance process using a parallel solution: a maintenance information management system based on a 3D information model in conjunction with a digital inspection system using image processing. Three-dimensional digital models are required to utilise information from the entire lifecycle of a project, including design and construction, operation, and maintenance, by continuously exchanging and updating data from each stakeholder. For the maintenance of prestressed concrete bridges, the twin models are defined and their uses are presented.     

基于稳定理论的单斜式桁架优化设计

单斜式平行弦型钢桁架在实际工程中应用广泛,当跨度、荷载及材料、杆件截面形式一定时,桁架的用料及造价取决于腹杆的倾角。钢结构设计规范规定α角取值在[30°6,0°],但在设计中,α角究竟取何值才能使桁架用料最省、造价最低,对这个问题,至今理论上还没有明确的结论。本文针对该问题进行了研究,讨论了此类桁架结构参数的优化设计问题。在满足结构的强度及稳定条件的基础上,利用压杆稳定设计直接法建立优化设计的数学模型,使用数值方法进行求解,得出了α角最优值计算公式。通过算例分析进一步证明了本文结论的可靠性,为此类桁架结构的优化设计提供了理论依据。     

Optimal pricing and environmental improvement for a hazardous waste disposal supply chain with emission penalties

Hazardous waste management has become a municipal problem, associated with industrial development and changing consumption patterns. We study the hazardous waste management system as a supply chain with a disposal facility and a contractor, which serves customers with demand sensitive to price and environment impact. The government intervenes with this supply chain by imposing emission penalties that make the waste disposal facility responsible for reducing disposal process emissions. The Stackelberg game and Nash equilibrium are used to model the decision-making sequence between the disposal facility and the contractor. We specify different scenarios to model the hazardous waste management supply chain. The goal of this research is to find the optimal disposal service price and level of environmental improvement to mitigate adverse impacts and maximize profits. The applicability of dual-channel service in the hazardous waste supply chain is also investigated. Our study shows that the supply chain obtains the highest profit if both the disposal facility and the contractor operate in a centralized model. Under some scenarios, profitability improves if the disposal facility becomes active in waste collection and transportation under a dual-channel supply-chain model. Demand sensitivity to price and environmental impacts can affect the adopted level of improvement by disposal facilities.     

Relationship between quality of building maintenance management services for indoor environmental quality and occupant satisfaction

Two surveys were carried out to investigate the correlation between building maintenance management services for indoor environmental quality (IEQ) and occupant satisfaction. Each maintenance management organization manager was surveyed using the Evaluation Index of Maintenance Management Service Quality, created by Akira Takakusagi. Seven office buildings in Seoul, Korea were investigated in the first survey, and two buildings from the first survey were selected for analysis in the second survey. One is a building with good maintenance management services but low occupant satisfaction, and the other is an office building with low maintenance management services but high occupant satisfaction.