Multi-objective probabilistic optimization of bridge lifetime maintenance : novel approach

Due to the increase in deterioration of the existing civil infrastructure, in particular bridge networks, governments and highway agencies are trying to find methods that allow a consistent and rational management of existing bridges. In this paper, a novel approach is presented. This approach uses multi-objective probabilistic optimization over time and defines performance of existing bridges in terms of lifetime condition, safety, and cost. The proposed approach aims at providing a tool for optimal maintenance management policy definition of a large group of similar structures. Consequently, emphasis is put on the use of limited information and low computational cost. Applications to real cases are presented showing the applicability of the method as well as its advantages in terms of reduction of costs and improvements in performance.(undefined

Life-cycle performance of structures: combining expert judgment and results of inspection

Life-Cycle Civil Engineering – Biondini & FrangopolCurrent bridge management systems base decisions on the results of visual inspections. These systems consider visual inspection results as accurate and disregard any further information available. In the present study, the result of each inspection is considered as a random variable, dependent of a wide range of factors, that can be integrated with other sources of information, including expert judgment and results of other inspections. The combination of different sources of information results in reliable posterior information and allows more accurate predictions of future deterioration. In the present paper, performance of an existing structure is obtained in terms of the condition index, which describes the effects of deterioration as can be seen by an inspector, and the safety index, which measures the safety margin of the structure. The reduction in uncertainty associated with periodical inspections is considered through updating of performance profiles. The updating of the condition index is direct, as new information on this parameter is collected by the inspector. In terms of safety, however, only indirect information is collected and the uncertainty reduction associated with an inspection is significantly lower. Several realistic examples show the impact of inspections on the predicted life-cycle performance of structures.UNIC - Research Center in the New University of Lisbo

Life cycle analysis of reinforced concrete bridges in Baltic countries

During this paper the first part of Life Cycle Analysis based on visual inspection data of main types of reinforced concrete bridges in Baltic countries will be introduced and discussed. In a first step, the background of bridge management systems, visual inspections and most common bridges will be presented. During this step, an explanation of differences and similarities of Baltics visual inspections and data processing will be introduced. In a second step, principal component analysis with main outcomes for different Baltic countries and possible reasons for those outcomes will be discussed. Also a comparison of principal components for similar bridges in all Baltic countries will be shown. At the end, input for predictive models will be introduced. The main objective of this input is to show what elements deteriorate more rapidly and due to that have an influence for Life Cycle of reinforced concrete bridgesThe authors would like to gratefully acknowledge supporting of TU1406 – Quality specifications for roadway bridges, standardization at a European level (BridgeSpec), a COST Action supported by EU Framework Programme Horizon 2020.info:eu-repo/semantics/publishedVersio

Structural Health Monitoring Issues Using Inclinometers on Prestressed Concrete Girder Bridge Decks

In the last decades, assessment and rehabilitation of the existing built environment constitute one of the major challenges for engineers, practitioners and code-makers all over the world. Aging, deterioration processes, lack of or improper maintenance, and increasing occurrence of extreme events have led to the need of more efficient methods for the safety assessment and retrofitting/rehabilitation of existing concrete structures like bridges. New approaches deriving from research should be able to provide solutions devoted to reduce and/or avoid the necessity of interventions, verifying the safety conditions for human life and performances for serviceability on aged infrastructures. Structural Health Monitoring (SHM) of existing bridges has become a key issue in all western world as most of the infrastructures of each Country are reaching the end of their design life. SHM can be divided classically in two approaches: static and dynamic. Static SHM is based on the measure of displacements and their derivatives like rotations or strains regardless of the dynamic behaviour of the structure. Clinometers are among the most used devices to measure angles on structures; they can provide high accuracy when used in static mode as advanced techniques of signal processing can be used to reduce the noise of the signal working on acquisitions that can last several seconds to provide one single accurate measure of angle. Nevertheless, many issues one the affidability and the correct use of measures done with clinometers have to be addressed to achieve a trustworthy SHM using such devices. In this paper the most relevant issues related to the f.e.m. modelling of a bridge deck in view of the use of clinometers for SHM are presented providing explanation using a test case bridge that has been under continuous investigation for many months. A brief explanation of the process for data cleaning and interpretation is also given, stressing out the limits of the technology and the possible outcomes

Towards Dynamic Criticality-Based Maintenance Strategy for Industrial Assets

An asset’s risk is a useful indicator for determining optimal time of repair/replacement for assets in order to yield minimal operational cost of maintenance. For a successful asset management practice, asset-intensive organisations must understand the risk profile associated with their asset portfolio and how this will change over time. Unfortunately, in many risk-based asset management approaches, the only thing that is known to change in the risk profile of the asset is the likelihood (or probability) of failure. The criticality (or consequences of failure) of asset is assumed to be fixed and has considered as more or less a static quantity that is not updated with sufficient frequency as the operating environment changes. This paper proposes a dynamic criticality-based maintenance approach where asset criticality is modeled as a dynamic quantity and changes in asset’s criticality is used to optimize maintenance plans (e.g. determining the optimal repair time/replacement age for an asset over it life cycle period) to have a better risk management and cost savings. An illustrative example is used to demonstrate the effect of implementing dynamic criticality in determining the optimal time of repair for a bridge infrastructure. It is shown that capturing changes in the criticality of the bridge over time and using this understanding in the risk analysis of the bridge provided the opportunity for better maintenance planning resulting to reduction of the total risk

Probabilistic maintenance and optimization strategies for deteriorating civil infrastructures

In developed countries, civil infrastructures are one of the most significant investments of governments, corporations, and individuals. Among these, transportation infrastructures, including highways, bridges, airports, and ports, are of huge importance, both economical and social. Most developed countries have built a fairly complete network of highways to fit their needs. As a result, the required investment in building new highways has diminished during the last decade, and should be further reduced in the following years. On the other hand, significant structural deteriorations have been detected in transportation networks, and a huge investment is necessary to keep these infrastructures safe and serviceable. Due to the significant importance of bridges in the serviceability of highway networks, maintenance of these structures plays a major role. In this paper, recent progress in probabilistic maintenance and optimization strategies for deteriorating civil infrastructures with emphasis on bridges is summarized. A novel model including interaction between structural safety analysis,through the safety index, and visual inspections and non destructive tests, through the condition index, is presented. Single objective optimization techniques leading to maintenance strategies associated with minimum expected cumulative cost and acceptable levels of condition and safety are presented. Furthermore, multi-objective optimization is used to simultaneously consider several performance indicators such as safety, condition, and cumulative cost. Realistic examples of the application of some of these techniques and strategies are also presented.The authors gratefully acknowledge the partial financial support of the U.K. Highways Agency and of the U.S. National Science Foundation through grants CMS-9912525 and CMS-0217290. The second author also acknowledges the support of the Portuguese Science Foundation (FCT)

In situ measured cross section geometry of old timber structures and its influence on structural safety

Old timber structures may show significant variation in the cross section geometry along the same element, as a result of both construction methods and deterioration. As consequence, the definition of the geometric parameters in situ may be both time consuming and costly. This work presents the results of inspections carried out in different timber structures. Based on the obtained results, different simplified geometric models are proposed in order to efficiently model the geometry variations found. Probabilistic modelling techniques are also used to define safety parameters of existing timber structures, when subjected to dead and live loads, namely self-weight and wind actions. The parameters of the models have been defined as probabilistic variables, and safety of a selected case study was assessed using the Monte Carlo simulation technique. Assuming a target reliability index, a model was defined for both the residual cross section and the time dependent deterioration evolution. As a consequence, it was possible to compute probabilities of failure and reliability indices, as well as, time evolution deterioration curves for this structure. The results obtained provide a proposal for definition of the cross section geometric parameters of existing timber structures with different levels of decay, using a simplified probabilistic geometry model and considering a remaining capacity factor for the decayed areas. This model can be used for assessing the safety of the structure at present and for predicting future performance.Fundação para a Ciência e a Tecnologia (FCT

In situ measured cross section geometry of old timber structures and its influence on structural safety

Old timber structures may show significant variation in the cross section geometry along the same element, as a result of both construction methods and deterioration. As consequence, the definition of the geometric parameters in situ may be both time consuming and costly. This work presents the results of inspections carried out in different timber structures. Based on the obtained results, different simplified geometric models are proposed in order to efficiently model the geometry variations found. Probabilistic modelling techniques are also used to define safety parameters of existing timber structures, when subjected to dead and live loads, namely self-weight and wind actions. The parameters of the models have been defined as probabilistic variables, and safety of a selected case study was assessed using the Monte Carlo simulation technique. Assuming a target reliability index, a model was defined for both the residual cross section and the time dependent deterioration evolution. As a consequence, it was possible to compute probabilities of failure and reliability indices, as well as, time evolution deterioration curves for this structure. The results obtained provide a proposal for definition of the cross section geometric parameters of existing timber structures with different levels of decay, using a simplified probabilistic geometry model and considering a remaining capacity factor for the decayed areas. This model can be used for assessing the safety of the structure at present and for predicting future performance

Compensation Factors for Bridges Built With a Reinforced Concrete Strength Below Its Nominal Value and Located on Seismic Hazard Zones

Sometimes, in the absence of a strict supervision, bridges are built with a reinforced concrete strength below its nominal value. If the difference is not so high to consider the bridge demolition, a question arises about how much the compensation should be. In this paper, a rational basis to orient negotiations, taken as the ratio between expected life-cycle costs for the actual and nominal concrete strengths is proposed and illustrated for a bridge in Mexico City. The calculation of the expected life-cycle cost includes the bridge annual failure probability under the dead, live and seismic loads and the costs of failure consequences. Uncertainty is considered only on the seismic load. The bridge annual failure probability is calculated by FORM approximation and by considering scenario ground accelerations and the seismic hazard curve for the bridge site. With the total probability theorem, the overall bridge annual failure probability is approximated and the expected life-cycle costs are calculated. The process is repeated for several values of reinforced concrete strength and the compensation factors are calculated and plotted for several costs of consequences. In order to explore several cases, two reinforced concrete strength, two pier heights: 4 and 8 m, three sites in Mexico with different seismicity and three levels of failure consequences, are considered. In these examples, the dominant failure mode is the pier axial load-bending moment interaction as a result of the acting loads combination. As expected, the factors increase for a larger difference of concrete strengths, for the higher piers, for a stronger seismicity and for larger costs of failure consequences. The factors were calculated for a nominal concrete strength of 200 Kg/cm2, and variations of 180 and 160 Kg/cm2, and for a nominal strength of 420 Kg/cm2, and variations of 400 and 380 Kg/cm2