A performance‐based bridge LCCA model using visual inspection inventory data

Since most bridge life cycle cost analysis (LCCA) depends heavily on the analyst's experience to determine the times and costs of remedial actions over a bridge's lifetime, the results are often subject to question because of their subjectivity. While some work has been done over the years to develop reliable deterioration models for determining such times and costs, the proposed models often require sophisticated inspection data, which is costly to obtain, and/or complex mathematical calculations. A simple linear deterioration model based on visual inspection inventory data concerning bridge components is introduced and integrated into the LCC analysis. The proposed model provides an alternative approach to bridge LCC analysis that can improve the objectivity of analysis and does not require input of sophisticated inspection, and thus facilitates application of bridge life cycle cost analysis. The LCCA method developed in this study is applied to a case study of alternative PCI (Pre‐stressed Concrete I‐girder) and a PCB (Pre‐stressed Concrete Box‐girder) bridges for the purpose of model validation.     

Life-cycle reliability assessment of reinforced concrete bridges under multiple hazards

This paper proposes a novel probabilistic methodology for estimating the life-cycle reliability of existing reinforced concrete (RC) bridges under multiple hazards. The life-cycle reliability of an RC bridge pier under seismic and airborne chloride hazards is compared to that of a bridge girder under traffic and airborne chloride hazards. When conducting a life-cycle reliability assessment of existing RC bridges, observational data from inspections can provide the corrosion level in reinforcement steel. Random variables related with the prediction of time-variant steel weight loss can be updated based on the inspection results using Sequential Monte Carlo Simulation (SMCS). This paper presents a novel procedure for identifying the hazards that most threaten the structural safety of existing RC bridges, as well as the structural components with the lowest reliability when these bridges are exposed to multiple hazards. The proposed approach, using inspection results associated with steel weight loss, provides a rational reliability assessment framework that allows comparison between the life-cycle reliabilities of bridge components under multiple hazards, helping the prioritisation of maintenance actions. The effect of the number of inspection locations on the updated reliability is considered by incorporating the spatial steel corrosion distribution. An illustrative example is provided of applying the proposed life-cyle reliability assessment to a hypothetical RC bridge under multiple hazards.     

Practical valuations on the effect of two type uncertainties for optimum design of cable-stayed bridges

A procedure for the optimum structural design of cable-stayed bridges is proposed based on minimum expected life-cycle cost (LCC); the procedure is illustrated with the optimum design of a cable-stayed bridge subjected to static and earthquake loads. Reliability analysis of the bridge is performed taking into account the two types of uncertainty in the capacity and loads. The capacity of the bridge is assumed to be determined by its critical members; this is tantamount to the assumption that the capacities and load effects of the structural members are highly correlated. Various designs of a cable-stayed bridge are considered; namely, a standard design, plus several that are weaker as well as several that are stronger than the standard design. For the different alternative designs, the member sections are decreased or increased relative to those of the standard design. The LCC of a particular design is formulated assuming that the cost components (including the maintenance and social costs) are respectively fractions of the initial cost. Reliability of a design associated with the aleatory uncertainties is assessed for each design, and the corresponding expected LCC and safety index are evaluated. The results of the various designs provide the information, safety index vs expected LCC, for determining the design with the minimum expected LCC which can be presented graphically. Because of the epistemic type of uncertainty, the LCC as well as the safety index of the optimum design are random variables; the respective histograms are also generated, from which the various percentile values can be obtained. Especially, the 75% and 90% values of the LCC may be specified to minimize the chance of underestimating the actual LCC of the optimum design; similarly the 75% and 90% values of the safety index may be specified for a conservative design of the cable-stayed bridge.     

Seismic life-cycle cost analysis of ageing highway bridges under chloride exposure conditions: modelling and recommendations

Chloride-induced corrosion of highway bridges constitutes a critical form of environmental deterioration and may result in significant escalation of seismic life-cycle costs due to increased fragility during earthquake events. Most of existing literature tends to adopt simplistic uniform area loss assumptions in lieu of potentially complex, yet realistic and more detrimental, pitting corrosion models for seismic vulnerability analysis. Since the degree of deterioration depends on the severity and duration of exposure, there exists a need to investigate the influence of uniform vs. pitting corrosion assumption on seismic life-cycle costs for varied chloride exposure conditions. A case-study example of a highway bridge in Central and Southeastern US reveals consideration of pitting corrosion as critical for extreme exposures compared to relatively minor settings. Subsequently this study provides recommendations to aid bridge engineers and stakeholders to balance between computational cost and accuracy of results to aid prompt decisions on rehabilitation of ageing bridges in different exposure conditions. A framework is also included to compute seismic life-cycle costs from generic measures of corrosion, independent of assumed exposure scenario. This framework is particularly helpful for seismic loss assessment of highway bridges in chloride exposure zones with periodic field measurements to estimate the extent of structural deterioration.     

Corrosion initiation time updating by epistemic uncertainty as an alternative to schedule the first inspection time of pre-stressed concrete vehicular bridge beams

As traffic demands grow constantly and some vehicle bridges deteriorate because of corrosion issues, bridge agencies require non-expensive procedures to support decisions about cost-effective maintenance schedules. In this article, a reliability-based formulation is proposed for the prediction of the optimal first inspection time including both the corrosion deterioration and the epistemic uncertainty on the corrosion initiation time. For the identification of the bridge integrity state, where little or no follow-up has been previously developed, the prediction of a damage state implies a great deal of epistemic uncertainty. The impact of this kind of uncertainty on the corrosion initiation time prediction is appraised in order to include the conservative estimations of such a time, according to the bridge revenues/cost ratio of further and more detailed studies. The time-varying bridge reliability is calculated in terms of the bridge corrosion deterioration, which induces a moment capacity reduction of the bridge beams. Epistemic uncertainty is introduced in the corrosion initiation time, and the optimal first inspection time is obtained as a probability distribution. Consequently, a procedure to calculate the first time for inspection on girder bridges has been proposed, based on updating a known distribution after considering the effect of epistemic uncertainty, using a lognormal distributed factor as ‘evidence’, by means of the Markov chain Monte Carlo technique.     

谈钢桥设计的新型方法-寿命周期成本

主要针对钢桥有效的寿命周期成本(LCC)的优化设计中实际产生的LCC进行了简要的描述和规定。一般钢桥优化设计的LCC模型中,包括钢结构桥梁的初始成本和直接/间接的修复成本,维修/更换成本,材料损坏或者疲劳损失,道路使用者的成本,间接的经济损失。因此,论文着重介绍一般配方的模型和适合实际操作的钢桥有效的LCC系统模型设计。     

A stakeholder probability-based optimization approach for cost-effective bridge management under financial constraints

Management of bridges under uncertainty is an important issue for stakeholders. The use of probabilistic approaches enables one to consider uncertainties in the structural deterioration, assessment, and maintenance processes. Combined with optimization techniques, it is possible to determine management strategies that simultaneously minimize failure, assessment, maintenance, and rehabilitation costs. Nevertheless, there is a strong need in developing practical and efficient frameworks that enable stakeholders to optimize future allocation of budgets for facilities under uncertain structural parameters. In particular, providing an approach that is in agreement with stakeholders constraints still remains a challenge. Moreover, the use of structural health monitoring (SHM) in future management frameworks, to update structural performance, still needs further development. The objective of this paper is threefold: (a) provide management strategies in agreement with fixed budgets, (b) provide management strategies that consider the time delay between the assessment and the intervention schedule, and (c) include information provided by SHM in the decision process and analyze the impact of monitoring strategies on the structural analysis accuracy. An event tree based approach is proposed to consider various uncertainties in the decision process. Optimal solutions are associated with multiple criteria such as minimum expected failure cost, minimum expected inspection/SHM/maintenance costs, maximum agreement of expected inspection/SHM/maintenance costs to available budgets, and maximum accuracy of monitoring results. The approach is illustrated on an existing highway bridge.     

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.     

沿海桥梁混凝土结构腐蚀调查及分析

针对日照沿海桥梁的耐久性现状进行调研,通过对桥梁墩身、边梁和栏杆混凝土的保护层厚度、碳化深度以及桥梁不同部位的游离氯离子浓度的检测表明:桥梁混凝土结构保护层厚度偏小、车辆超载、结构设计不合理、施工管理不当、缺乏维护管理是导致沿海桥梁混凝土结构损伤劣化的主要原因。此外,海洋环境中的氯离子和空气中的二氧化碳将导致桥梁混凝土中钢筋腐蚀,海水中的盐在混凝土中结晶将导致桥梁墩身腐蚀破坏。     

Development of the Swedish bridge management system by upgrading and expanding the use of LCC

Although many bridge management systems (BMSs) contain some forms of life-cycle costing (LCC), the use of LCC in bridge engineering is limited. Life-cycle costing in many BMSs has mainly been applied within the bridge operation phase to support decisions related to existing bridges. Life-cycle costing has several useful applications within the bridge entire life, from cradle to grave. This article introduces the Swedish Bridge and Tunnel Management System (BaTMan). A comprehensive integrated LCC implementation scheme will be illustrated, taking into account the bridge investment and management process in Sweden. The basic LCC analysis tools as well as other helpful techniques are addressed. A real case study is presented to demonstrate the recent improvement of BaTMan practically in the function of whether to repair or to replace a bridge. Cost records for 2508 bridges are used as input data in the presented case study. Considering the same records, the average real and anticipated initial costs of different bridge types in Sweden will schematically be presented.     

Risk-based maintenance strategy for deteriorating bridges using a hybrid computational intelligence technique: a case study

The current bridge inspection and maintenance protocol that is used in most countries focuses primarily on the visible aspects of bridge fitness and underestimates the invisible aspects, such as resistance to scouring and earthquake hazards. To help transportation authorities to better consider both aspects, the present study developed a new computational intelligence system, the so-called risk-based evaluation model for bridge life-cycle maintenance strategy (REMBMS). This model considers the three main risk factors of component deterioration, scouring and earthquakes in order to minimise the expected life-cycle cost of bridge maintenance. Monte Carlo simulation is used to estimate the probability of bridge maintenance. The evolutionary support vector machine inference model (ESIM) was applied to estimate the risk-related maintenance cost using historical data from the Taiwan Bridge Management System (TBMS) database. The time-influenced expected costs were obtained by multiplying each maintenance probability with its associated cost. Finally, the symbiotic organisms search (SOS) algorithm is used to identify the bridge maintenance schedule that optimises the life-cycle maintenance cost. The present study provides to bridge management authorities an effective approach for determining the optimal timing and budget for maintaining transportation bridges.     

Spannglieder mit Kunststoffhüllrohren zur Herstellung von Brücken ohne Betonstahlbewehrung

Tendons with Plastic Ducts for Bridges without Mild Steel Reinforcement Frequently the conventional sealing of concrete bridges does not show a satisfactory serviceability in practice. Imperfect sealing leads to chloride entry into the structure because of bending cracks in the upper side of bridges in the range of negative moments. If a road passes under a bridge, there is the risk of chloride entry caused by salt fog spread on the surface of the bridge. In addition to the restoration liability of the sealing the pavement requires regular repair work. This periodic repair work causes high costs and affects the traffic flow. The method presented in this paper is characterized by omitting corrosion‐sensitive reinforcement and by integrating the pavement in the structure. The aim is to create concrete bridges with improved durability which can be manufactured with comparable costs to conventional concrete bridges. The results of experimental tests on the structural behavior of such structures will be presented.     

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.     

Time-variant reliability profiles for steel girder bridges

Evaluation of existing steel bridges becomes more important due to natural aging, increasing load spectra, deterioration caused by corrosion, and other problems. In the result, bridge structures exposed to aggressive environmental conditions are subjected to time-variant changes of resistance. Therefore, there is a need for evaluation procedures for an accurate prediction of the load carrying capacity and reliability of bridge structures, in order to make rational decisions about repair, rehabilitation, and expected life-cycle costs. The objective of this paper is to develop time-variant reliability models for steel girder bridges. Traditional methods based on deterministic analysis do not reveal the actual load carrying capacity of the structure. The proposed approach is based on reliability analysis of components and structural systems. The study involves the selection of representative structures, formulation of limit state functions, development of load models, development of resistance models for corroded steel girders, development of the reliability analysis method, reliability analysis of selected bridges, and development of the time-dependant reliability profiles including deterioration due to corrosion. The results of the study can be used for a better prediction of the service life of deteriorating steel girder bridges, and development of optimal reliability-based maintenance strategies.     

Risk assessments of long-span bridges considering life-cycle cost concept and near-fault ground motion effect

The influence of the near-fault ground motion on the response of long-span bridges must be considered as a critical factor for seismic design because the response indicates different aspects from existing earthquake characteristics. Also, it is important to note that the safety index for the risk assessment of long-span bridges is determined based on the minimum expected life-cycle cost E(LCC). In this study, earthquake characteristics are analyzed by creating elastic and inelastic response spectrums with actual measurement records (Chi-Chi earthquake records) and then the numerical analysis of the long-span bridge in Namhae, Korea is performed according to the increase and reduction of the member stiffness based on the standard design., the reliability evaluation of the long-span bridge considering aleatory uncertainties is performed on the basis of the combined results of static analysis and seismic response analysis. Also, the minimum LCC is estimated based on failure probabilities by the different alternative design. Because of epistemic uncertainties, the results of reliability evaluation and the LCC of optimal design are selected as random variables; the safety index, failure probability and expected minimum LCC are re-evaluated with regard to critical percentage values for a risk-averse design of the long-span bridge, and are presented graphically using cumulative percentages. It is, therefore, expected that this study will provide the basic information for the risk assessment and optimal design method in performing seismic design of the long-span bridge considering earthquake characteristics.     

Spatial variability of damage and expected maintenance costsfor deteriorating RC structures

The paper develops a technique to predict life-cycle costs, using probabilistic information about the likelihood and extent of corrosion-induced cracking to reinforced concrete (RC) structures. The present paper focuses on the likelihood and extent of severe cracking as the criterion for the timing and cost of maintenance. The life-cycle cost and expected maintenance cost considers multiple repairs and various inspection intervals over the service life of the structural element. A repair cost function is also developed. Two common maintenance strategies are considered: repair and rehabilitation. It was found that for a 2% discount rate the benefits of delaying the timing of repairs outweigh the cost of increased extent of damage, for maintenance of a RC bridge deck.     

Critical issues,condition assessment and monitoring of heavy movable structures: emphasis on movable bridges

In this paper, a relatively less studied class of structures is presented based on the research conducted on Florida's movable bridges over the last several years. Movable bridges consist of complex structural, mechanical and electrical systems that provide versatility to these bridges, but at the same time, create intermittent operational and maintenance challenges. Movable bridges have been designed and constructed for some time; however, there are fewer studies in the literature on movable bridges as compared to other bridge types. In addition, none of these studies provide a comprehensive documentation of issues related to the condition of movable bridge populations in conjunction with possible monitoring applications specific to these bridges. This paper characterises and documents these issues related to movable bridges considering both the mechanical and structural components. Considerations for designing a monitoring system for movable bridges are also presented based on inspection reports and expert opinions. The design and implementation of a monitoring system for a representative bascule bridge are presented along with long-term monitoring data. Various movable bridge characteristics such as opening/closing torque, bridge balance and friction are shown since these are critical for maintenance applications on mechanical components. Finally, the impact of environmental effects (such as wind and temperature) on bridge mechanical characteristics is demonstrated by analysing monitoring data for more than 1000 opening/closing events.     

Development of a life cycle cost estimate system for structures of light rail transit infrastructure

In recent years, the need and demand for the construction and utilization of light rail transit have been on the rise in Korea. As light rail transit construction projects have typically been promoted as Build–Transfer–Lease (BTL) projects, the private companies involved need to perform economic feasibility analysis by estimating life cycle cost (LCC) quickly and accurately. The success of a project greatly depends on the accurate analysis of the initial investment cost from the stages of design through construction, operating cost for the stages of operation and maintenance, and profits from operation. While such an LCC analysis requires a variety of experience with construction projects, a significant base of performance data and related expertise, Korean companies have no experience in the field of light rail transit construction, and the operating data is meager. With a lack of experience and data, the parties involved with light rail transit construction projects have come up with diverse costs estimates based on highly inaccurate data. Accordingly, it is urgent that there is a method to support the parties involved with light rail transit projects, particularly the private companies taking responsibility for investment in and operation of the light rail transit.This research aims to estimate the approximate construction cost of light rail transit structures (e.g. bridge, tunnel, etc.) and to develop an economic feasibility analysis system for light rail transit structures taking LCC into account based on the already calculated cost in order to support a reasonable decision-making process in relation with light rail transit construction projects.To estimate construction cost, major factors that have a great influence on the construction cost of the structure were first selected, and then a database for each unit cost was built. Using the system, a user can automatically calculate the construction cost by selecting the structure type and the engineering technique. For the LCC analysis, research of the literature was conducted, and based on the research an LCC analysis procedure and model was determined. In addition, by reviewing the uncertainty factors and the cost classification system appropriate for the construction of a light rail transit structure, the LCC analysis algorithm was written. Using the algorithm, LCC analysis of a bridge for a light rail transit was conducted to verify the feasibility of the algorithm that can provide information used for major decision-making, based on which private companies can determine whether or not to participate in a light rail transit construction project. This research has its own significance, both as a system to estimate construction cost for a light rail transit project based on diverse information, and as a system to analyze economic feasibility for LCC prediction.     

A two‐level mixed‐integer programming model for bridge replacement prioritization

A bridge network is an essential part of the transportation system. Therefore, the restoration and replacement activities of aging bridges result in severe traffic delays and disruptions that heavily impact the daily traffic. Accelerated bridge construction (ABC) techniques are rapidly gaining acceptance as an alternative to conventional construction due to reduced construction duration and minimum closure impact at the network level. The limitations and completion rates vary depending on types of ABC. There is a trade‐off between a faster ABC technique with higher investment and a faster construction of a critical bridge in the network resulting large savings to users. To provide a balanced portfolio of ABC techniques on bridge sites and the prioritization of bridges for replacement, this paper develops a mixed‐integer programming (MIP) model with two levels. In this model, a network‐level scheme is used to select bridges for rapid replacement based on their criticality to the network, and a project‐level scheme is used to optimize the choice of ABC techniques for each selected bridge. To account for the effects of different construction strategies for bridge replacement, the costs associated with each replacement activity are calculated, including direct costs from the actual replacement of bridges and indirect costs experienced by network users due to bridge closures during maintenance. Using the MIP model and based on investment, outcomes are estimated for the enhanced serviceability, efficient ABC techniques, an optimal bridge replacement strategy, and minimized total cost during the entire process. These outcomes could provide decision makers and stakeholders with a complete understanding of the prioritization process at both the network and project levels.     

Life-cycle evaluation of deteriorated structural performance of neutralised reinforced concrete bridges

For existing reinforced concrete (RC) bridges, the structural performance is highly dependent on the changing properties of concrete and reinforcing steel due to neutralisation-induced corrosion. As neutralisation progresses, the corrosion could become serious enough to deteriorate not only the serviceability, but also the maintainability, of the structural performance. To study the influence of neutralisation on the existing RC bridges, the inspected data and test results collected from 21 bridges in Taiwan were examined to obtain the essential parameters through regression analyses. The regressive parameters related to service time can be employed in evaluating the variation of material and sectional properties in both reinforcements and concrete, and, accordingly, the change of structural performance from time to time could be obtained quantitatively via structural analysis. As a consequence, the performance degradation curve of an existing RC bridge can be predicted and, if necessary, the appropriate timing for repair or retrofit could be suggested. The results obtained could facilitate the minimisation of life-cycle cost for the neutralised RC bridges and enhance the functionality of a bridge management system (BMS).