Bridge Annual Maintenance Prioritization under Uncertainty by Multiobjective Combinatorial Optimization

Abstract:   Bridge managers are facing ever-increasing tasks of prioritizing limited budgets to cost-effectively maintain normal functionality of a huge inventory of deteriorating civil infrastructures such as highway bridges over the life cycle. A satisfactory maintenance planning scenario should meet managers' specified requirements for the optimum balance between whole-life costing and structural performance. This article presents a general computational procedure to prioritize on an annual basis maintenance efforts for deteriorating reinforced concrete bridge crossheads over a designated time horizon. Within each year, none or one of the available maintenance types with different performance improvement capabilities could be applied and the time of application for any maintenance intervention is considered to be uniformly distributed within a 1-year time interval. Effects of uncertainties associated with bridge crosshead deterioration processes with and without maintenance interventions are considered by means of Monte Carlo simulation to predict probabilistically structural performance and life-cycle maintenance cost. The resulting combinatorial optimization problem is automated by a multiobjective genetic algorithm. It produces a group of different sequences of annualized maintenance interventions that lead to optimized tradeoff among condition, safety, and life-cycle cost objectives. This enables bridge managers to determine a preferred annual maintenance prioritization solution by comparing different alternatives.     

Bridge life-cycle performance and cost: analysis,prediction, optimisation and decision-making

The development of a generalised framework for assessing bridge life-cycle performance and cost, with emphasis on analysis, prediction, optimisation and decision-making under uncertainty, is briefly addressed. The central issue underlying the importance of the life-cycle approach to bridge engineering is the need for a rational basis for making informed decisions regarding design, construction, inspection, monitoring, maintenance, repair, rehabilitation, replacement and management of bridges under uncertainty which is carried out by using multi-objective optimisation procedures that balance conflicting criteria such as performance and cost. A number of significant developments are summarised, including time-variant reliability, risk, resilience, and sustainability of bridges, bridge transportation networks and interdependent infrastructure systems. Furthermore, the effects of climate change on the probabilistic life-cycle performance assessment of highway bridges are addressed. Moreover, integration of SHM and updating in bridge management and probabilistic life-cycle optimisation considering multi-attribute utility and risk attitudes are presented.     

Maintenance optimization of infrastructure networks using genetic algorithms

This paper presents an approach to determining the optimal set of maintenance alternatives for a network of infrastructure facilities using genetic algorithms. Optimal maintenance alternatives are those solutions that minimize the life-cycle cost of an infrastructure network while fulfilling reliability and functionality requirements over a given planning horizon. Genetic algorithms are applied to maintenance optimization because of their robust search capabilities that resolve the computational complexity of large-size optimization problems. In the proposed approach, Markov-chain models are used for predicting the performance of infrastructure facilities because of their ability to capture the time-dependence and uncertainty of the deterioration process, maintenance operations, and initial condition, as well as their practicality for network level analysis. Data obtained from the Ministére des Transports du Québec database are used to demonstrate the feasibility and capability of the proposed approach in programming the maintenance of concrete bridge decks.     

Maintenance and management of civil infrastructure based on condition,safety, optimization,and life-cycle cost∗

Cost-competent maintenance and management of civil infrastructure requires balanced consideration of both the structure performance and the total cost accrued over the entire life-cycle. Most existing maintenance and management systems are developed on the basis of life-cycle cost minimization only. The single maintenance and management solution thus obtained, however, does not necessarily result in satisfactory long-term structure performance. Another concern is that the structure performance is usually described by the visual inspection-based structure condition states. The actual structure safety level, however, has not been explicitly or adequately considered in determining maintenance management decisions. This paper reviews the recent development of life-cycle maintenance and management planning for deteriorating civil infrastructure with emphasis on bridges using optimization techniques and considering simultaneously multiple and often competing criteria in terms of condition, safety and life-cycle cost. This multiple-objective approach leads to a large pool of alternative maintenance and management solutions that helps active decision-making by choosing a compromise solution of preferably balancing structure performance and life-cycle cost.     

Constraint-based clustering model for determining contract packages of bridge maintenance inspection

When a number of bridges are to be maintained yearly, contract engineers need to package certain bridges based upon the specified conditions. Traditional contract packaging is performed subjectively and manually. The purpose of this paper is to develop an objective and automatic decision-making process for contract packaging. Contract Packaging Technique (CPT), which is derived from k-prototypes, can determine appropriate contract packages by considering the inherent conditions of the infrastructure to be maintained. It can simultaneously handle user-specified constraints and mixed data types such as bridge locations, bridge types, bridge construction materials and maintenance costs. Validation was performed in this study to illustrate that the CPT can effectively divide a huge bridge maintenance plan into several appropriate contract units.     

Life cycle utility-informed maintenance planning based on lifetime functions: optimum balancing of cost,failure consequences and performance benefit

Decision-making regarding the optimum maintenance of civil infrastructure systems under uncertainty is a topic of paramount importance. This topic is experiencing growing interest within the field of life cycle structural engineering. Embedded within the decision-making process and optimum management of engineering systems is the structural performance evaluation, which is facilitated through a comprehensive life cycle risk assessment. Lifetime functions including survivor, availability, and hazard at component and system levels are utilised herein to model, using closed-form analytical expressions, the time-variant effect of intervention actions on the performance of civil infrastructure systems. The presented decision support framework based on lifetime functions has the ability to quantify maintenance cost, failure consequences and performance benefit in terms of utility by considering correlation effects. This framework effectively employs tri-objective optimisation procedures in order to determine optimum maintenance strategies under uncertainty. It provides optimum lifetime intervention plans allowing for utility-informed decision-making regarding maintenance of civil infrastructure systems. The effects of the risk attitude, correlation among components and the number of maintenance interventions on the optimum maintenance strategies are investigated. The capabilities of the proposed decision support framework are illustrated on five configurations of a four-component system and an existing highway bridge.     

A Petri-Net-based modelling approach to railway bridge asset management

Management of a large portfolio of infrastructure assets is a complex and demanding task for transport agencies. Although extensive research has been conducted on probabilistic models for asset management, in particular bridges, focus has been almost exclusively on deterioration modelling. The model being presented in this study tries to reunite a disjointed system by combining deterioration, inspection and maintenance models. A Petri-Net modelling approach is employed and the resulting model consists of a number of different modules each with its own source of data, calibration methodology and functionality. The modules interconnect providing a robust framework. The interaction between the modules can be used to provide meaningful outputs useful to railway bridge portfolio managers.     

Gestalten von Eisenbahnbrücken

Design of railway bridges. Railway bridges are high performance structures concerning their load bearing capacity, durability and serviceability. But high demands of usage and loading combined with the special conditions of building technology under continuing traffic led to a lack of aesthetic bridge design during the last decades. The structures of infrastructure, and in particular bridges, are large and tend to dominate their natural or urban environments. Bridges must, therefore, meet high levels of aesthetic and design value in addition to meeting the basic requirements of providing safety, functionality and economic solutions. Two years ago an advisory board for bridge design was established to support the Deutsche Bahn in making considerable improvements to the aesthetic and design quality of bridges promoting innovation in bridge design and construction.     

Bridge condition modelling and prediction using dynamic Bayesian belief networks

The development of a condition-based deterioration modelling methodology at bridge group level using Bayesian belief network (BBN) is presented in this paper. BBN is an efficient tool to handle complex interdependencies within elements of engineering systems, by means of conditional probabilities specified on a fixed model structure. The advantages and limitations of the BBN for such applications are reviewed by analysing a sample group of masonry bridges on the UK railway infrastructure network. The proposed methodology is then extended to develop a time dependent deterioration model using a dynamic Bayesian network. The condition of elements within the selected sample of bridges and a set of conditional probabilities for static and time dependent variables, based on inspection experience, are used as input to the models to yield, in probabilistic terms, overall condition-based deterioration profiles for bridge groups. Sensitivity towards various input parameters, as well as underlying assumptions, on the point-in-time performance and the deterioration profile of the group are investigated. Together with results from ‘what if’ scenarios, the potential of the developed methodology is demonstrated in relation to the specification of structural health monitoring requirements and the prioritisation of maintenance intervention activities.     

A random field based technique for the efficiency enhancement of bridge network life-cycle analysis under uncertainty

Studies associated with distributed civil infrastructure systems are usually very demanding from a computational point of view, especially when they involve life-cycle analysis, uncertainty, and optimization. For this reason, computational tools that enhance the efficiency of the analysis and make it feasible for complex practical applications are of utmost importance. In this paper, a computational technique for the efficiency enhancement of bridge network life-cycle analysis under uncertainty is presented and its impact in terms of CPU time reduction is investigated.The proposed technique consists in the joint use of random field theory and probabilistic reliability models for the simulation of the individual bridge service states over the life-cycle of the infrastructure. This random field based approach is extremely efficient and takes simultaneously into account the deterioration in time of the bridge reliability and the correlation in space of the service states of bridges belonging to the same transportation network. Compared to other techniques previously used to perform the same task, the proposed methodology is theoretically more solid and improves the computational efficiency by more than two orders of magnitude.A numerical example is provided to validate the proposed technique. Moreover, a second example involving the life-cycle performance analysis of a complex bridge network in Santa Barbara, CA, is presented.     

Life cycle assessment of a railway bridge: comparison of two superstructure designs

Railway bridges currently encounter the challenges of increasing the load capacity while the environmental sustainability should be achieved. However, it has been realised that the environmental assessment of railway bridges has not been integrated into the decision-making process, the standard guideline and criterion is still missing in this field. Therefore, the implementation of life cycle assessment (LCA) method is introduced into railway bridges. This article provides a systematic bridge LCA model as a guideline to quantify the environmental burdens for the railway bridge structures. A comparison case study between two alternative designs of Banafjäl Bridge is further carried out through the whole life cycle, with the consideration of several key maintenance and end-of-life scenarios. Six impact categories are investigated by using the LCA CML 2001 method and the known life cycle inventory database. Results show that the fixed-slab bridge option has a better environmental performance than the ballasted design due to the ease of maintenances. The initial material manufacture stage is responsible for the largest environmental burden, while the impacts from the construction machinery and material transportations are ignorable. Sensitivity analysis illustrates the maintenance scenario planning and steel recycling have the significant influence on the final results other than the traffic disturbances.     

A simplified management procedure for bridge network maintenance

Structural problems due to corrosion, ageing, durability, aggressive environments, materials defects, lack of ductility and unforeseen behaviour under seismic loads may significantly compromise the resistance and safety of bridges. Scheduled maintenance of bridges becomes important to ensure complete serviceability of the road network. Among existing bridge management systems (BMSs), this work is a contribution to the evaluation criteria of bridge condition by means of visual inspection, prediction of future structural condition and planning of maintenance intervention. After a brief review of some existing BMSs, a simple new procedure for evaluation of bridge condition by means of visual inspection, aimed at general planning of maintenance in a BMS framework, is presented in this paper. This procedure is applied to stock, including about 200 bridges and viaducts, of the Veneto region road network in the north-eastern part of Italy, and is then discussed.     

浅谈公路桥梁普通检测

针对桥梁养护管理工作的重要性,主要研究了公路桥梁普通检测的目的、工作程序、具体检测过程以及检测结果的评价方法,从而为养护管理提供了直接的数据和依据,并为具体从事桥梁检测的人员提供了一定的帮助。     

A Geographic Information System (GIS)–Based Bridge Management System

Many bridge authorities responsible for the management and maintenance of bridges in their road networks use computer-based databases or bridge management systems (BMSs) as data management and analysis tools to aid them in performing many important bridge management functions and decisions. Due to superior spatial data handling capabilities, geographic information system (GIS) technology is increasingly being considered for implementation in many infrastructure planning and management systems, including bridge management systems. This article describes the use of a hybrid business and information modeling approach to develop a model to support the development of a geographic information system (GIS)–based bridge management system. It presents the architecture for implementing such a system for the Bridge Unit of the Public Works Department (JKR) in Malaysia. Most GIS systems are technology-based. The methodology used here captures organizational processes as well as information systems requirements. This facilitates business decision making and business process change. Using this hybrid modeling approach, first the organization's business objectives, functions, and processes are modeled. These business requirements form the basis of detailed information requirement analysis. Object-oriented methods are then employed to define object models and show the relationships between objects and the operations performed on them. Finally, the software architecture and interface for developing such a prototype GIS-based BMS is described and some sample screen outputs of the system to analyze and visualize over 2500 actual Malaysian bridge structures in the road network are presented. Future developments of the infrastructure set out here are capable of providing a BMS that supports business processes and facilitates business process change.     

A condition assessment method for roadside assets

Infrastructure condition assessments provide key information for monitoring the quality of infrastructure, planning and budgeting of maintenance and rehabilitation activities and establishing performance goals. Although the literature is rich in condition assessment methods for roadway pavement and bridges (and to some extent for traffic signs), it is lacking such methods for roadside assets. This paper describes the development and validation of a condition assessment method for 12 roadside asset types and maintenance activities that are related to roadway safety, drainage, cleanliness and vegetation. These assets and maintenance activities are located in the area between the outside edges of the outside shoulders and the right-of-way boundaries. On divided highways, the median is also included. The developed condition assessment method consists of a set of performance standards, a visual inspection procedure to assess compliance with these standards and a statistical analysis procedure to determine the roadside level of service. To test and validate the developed method, it was applied to five highway corridors in Texas, USA, representing different climatic conditions, topography, traffic volume and population density (urban vs. rural). These field trials provided insights into the developed method, including practicality, reproducibility and probability distribution function which best represents the sample unit score.     

A risk and criticality-based approach to bridge performance data collection and monitoring

Bridges constitute a substantial and vital part of any transport infrastructure system. The functionality of the system is therefore reliant on the asset management strategies adopted for its bridges. To understand and manage bridge performance, data of appropriate quality has to be collected in a cost-efficient way and closely linked to the decisions made with it. To ensure a coherent approach, a data collection strategy for asset management of road bridges has been developed in this study. In the strategy, a combined risk and criticality-based approach is used to prioritise each bridge and to assign it to one of three data collection levels comprising core, intermediate and advanced. For each collection level, the strategy provides guidance on the type of data to collect, the accuracy and precision required in the data collection process, the frequency of inspections, and the recommended collection techniques to be used, including visual inspection, non-destructive evaluation and structural health monitoring. The strategy will help asset managers to develop a deeper level of knowledge on the bridges that have the greatest impact on the system functionality and to collect data of the required quality needed for the decisions they make.     

Multihazard resilience of highway bridges and bridge networks: a review

Abstract

Assessment of resilience for engineered systems has drawn ample attention from the engineering community in recent years. It has resulted in a significantly large body of literature focusing on pertinent areas of resilience. This article provides a systematic and comprehensive review of the literature addressing resilience assessment of bridges and bridge networks under single hazard and multihazard conditions. Though not much work been performed yet on multihazard resilience of bridges, relevant aspects including combinations of multiple hazards for bridge performance evaluation, methods for loss assessment and approaches taken for post-event recovery are discussed. Furthermore, maintenance is a key component if resilience is assessed in a life-cycle framework. Hence, available maintenance plans and strategies and their probable applications for bridges and bridge networks are discussed. The article concludes with a discussion on the need for further research in the focus area and challenges involved with the same.     

Considerations on recent trends in, and future prospects of, steel bridge construction in Japan

In this paper, consideration is given on recent trends in, and requirements for a bright future of, steel bridge construction in Japan. As far as recent trends are concerned, it is observed that the construction of long and big steel bridges has practically been completed. Consequently, the focus of recent main works is the maintenance of superannuated (overaged) bridges and the seismic retrofitting of existing bridges. The refreshment and regeneration of some superannuated bridges is also needed recently in order to mitigate the uncomfortable influence of these bridges on their surrounding environment. As for a bright future in steel bridge construction, first and foremost it is emphasized that the steel bridge industry should be able to attract, train and retain better students and engineers. For this purpose, maintenance and retrofitting works should be economically reasonable jobs. The necessity and importance of these works should be understood by the nation through retrofitting existing bridges against disasters and mitigating the unfavourable influence of bridge structures on the bridge environment on the basis of the code of ethics for civil engineers promulgated by JSCE. Moreover, bridge engineers should seek better social status and the bridge engineering field should become attractive to young students who will bear the future of this field.     

Comparison of Two Evolutionary Algorithms for Optimization of Bridge Deck Repairs

Abstract:   Prioritization of bridge decks for maintenance and repair purposes involves decisions related to project-level repair strategies as well as network-level selection of bridges that bring the highest return on the repair budget. These decisions, however, represent complex optimization problems that traditional optimization techniques are often unable to solve. This article introduces an integrated model for bridge deck repairs with detailed life cycle costs of network-level and project-level decisions. Two evolutionary-based optimization techniques that are capable of handling large-size problems, namely Genetic Algorithms and Shuffled Frog Leaping, are then applied on the model to optimize maintenance and repair decisions. Results of both techniques are compared on case study problems with different numbers of bridges. Based on the results, the benefits of the bridge deck management system are illustrated along with various strategies to improve optimization performance.     

Concept and requirements of sustainable development in bridge engineering

The concept of sustainability is described in this paper using a single sustainable principle, two goals of sustainable development, three dimensions of sustainable engineering, four sustainable requirements and five phases of sustainable construction. Four sustainable requirements and their practice in China are discussed in particular. The safe reliability of bridges is first compared with the events of bridge failure in China and in the rest of the world and followed by structural durability, including the cracking of concrete cable-stayed bridges, deflection of concrete girder bridges and fatigue cracks of orthotropic steel decks. With respect to functional adaptability, lateral wind action on vehicles and its improvement are introduced regarding a sea-crossing bridge located in a typhoon-prone area. The Chinese practice of using two double main span suspension bridges and a twin parallel deck cable-stayed bridge is presented in discussing the final sustainable requirement: capacity extensibility.