ABSTRACT:As reliability based methods gain increased acceptance, there is greater opportunity to use scarce resources more efficiently while maintaining a prescribed level of reliability of a structure throughout its service life. The goal is to provide management decisions that will balance lifetime system reliability and expected lifecycle cost in an optimal manner. This study proposes a system reliability approach for optimizing the lifetime repair strategy for highway bridges. The approach is demonstrated using an existing Colorado State highway bridge. The bridge is modeled as a series-parallel combination of failure modes, and the reliability of the overall bridge system is computed using time-dependent deterioration models and live load models. Based on an estab lished repair criterion, available repair options, repair costs, and updating, the optimum lifetime repair strategy is developed. The sensitivity of the optimum strategy to changes in various problem parameters including the prescribed service life, system failure criterion, and net discount rate is studied. Finally, the conclusions reveal that the proposed approach demonstrates real potential for practical applications, needs frequent updates through inspection, and requires considerable research effort to develop accurate input data.
Corrosion of reinforcement is a major problem affecting a large number of reinforced concrete structures. At present, most reliability-based design studies of reinforced concrete structures do not consider the effects of corrosion. In this paper, we present a reliability-based approach to the design of reinforced concrete bridge girders that are under corrosion attack. Both reserve and residual reliability constraints are satisfied. The approach is based on the American Association of State Highway and Transportation Officials (AASHTO) standard specifications for highway bridges and on data of chloride corrosion of steel in concrete. First, the effects of corrosion on both moment and shear reliabilities are investigated. Second, a reliability-based design approach based on minimization of total material cost including corosion effects is proposed. This approach is demonstrated on several design examples. Finally, we suggest and illustrate a reliability-based design approach based on minimization of expected lifetime cost including corrosion effects and cost of failure consequences.
Bridge management systems have become increasingly sophisticated over the past decade and provide valuable information about the structural condition of all bridges in the national database. At the same time, reliability methods have gained increasing prominence and are used to forecast life-cycle performance over many decades of structural life. Such reliability analyses need to be updated based on the results of inspections. Specifically targeted nondestructive evaluations are the preferred solution, but are not always available for every bridge. This paper examines how the visual inspection data provided from bridge management systems already in place can be used to update the reliability of a bridge. The limitations and necessary modifications to current practice are discussed. The superstructure of a Colorado highway bridge deteriorating due to corrosion is used as an example.
As both reliability analyses and systematic inspection programs for the world's infrastructure gain increased usage and promi nence, it becomes more important to use the information from routine visual inspections to update lifetime reliability assessments and resulting life-cycle inspection/repair strategies. The Army Corps of Engineers currently uses reliability analyses to economi cally justify the major rehabilitation of navigation structures. This paper illustrates how the Condition Index visual inspections for locks and dams can be modified and used to update the reliability analysis of a steel miter gate. The miter gates on two exist ing locks and dams along the Mississippi River are used as examples for corrosion and fatigue deterioration. The approach used is applicable to any structure where the inspection condition states are quantitative and a model exists to relate visual inspection results to the actual deterioration state of the structure.
ABSTRACT:A system reliability approach to minimizing the life-cycle cost of a deteriorating structure offers significant advantages such as a rational assessment of the assumed risk of failure, and an understanding of the importance and contribution of individual components to the overall reliability of the structure. The reliability of a structural system as a whole is the measure of its overall performance. This measure has to include both ultimate and serviceability limit states. A system model of a structure traditionally consists of a series-parallel combination of strength-based component limit states. Serviceability limit states however, can play a tremen dously important role in optimizing the inspection and repair of a deteriorating structure. This paper proposes the use of serviceability flags as a means to incorporate serviceability concerns into a strength-based reliability analysis. Using highway bridges as an example, available data sources for serviceability flags are considered. The effect of including serviceability flags in an optimum life-cycle analysis is illustrated on a specific highway bridge.
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