ABSTRACT
Traditional condition rating procedures concentrate on member condition and give little consideration to global structural behavior. In this paper a methodology is proposed to modify the correction factor applied during the assignment of bridge condition rating to account for bridge system behavior. Robustness and redundancy concepts, that have been used in the past for structural design of new bridges and for assessment of existing bridges, are in this work extended to condition rating. In this paper, corrosion of steel girders is considered as the main cause of material deterioration. By including the proposed correction factors, bridge inspectors will decrease condition ratings of less robust bridges that exhibit low levels of system capacity in their damaged state and increase the rating of robust bridges. Different system-based correction factors are assigned based on structural types and configurations, as well as the type, location, and extent of damage. The system-based correction factors proposed in this research are calibrated based on reliability index measures.
The aim of condition ratings is to assign a numerical value or a grammatical concept (good, bad, fair, …) that reflects the state of structural components of a bridge as well as non-structural parts. A correction factor, ϕs is exclusively applied to the strength term to define a corrected condition rating, I*: () I * = I s t r e n g t h ϕ s + I n o n − s t r e n g t h https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/eq141.tif"/>
where I* is the corrected condition rating, Istrength is the original condition rating related to the structural members contributing to system strength, Inon−strength is the original condition rating term related to the elements not contributing to system strength, ϕs is the system correction factor that accounts for the redundancy of a specific bridge type and configuration.
The Istrength term can itself be generalized through the following equation: () I s t r e n g t h = ∑ I d e t e r i o r a t e d ϕ r https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/eq142.tif"/>
where Idegteriorated is the term related to a specific level of deterioration detected in a structural member under inspection, ϕr is the robustness factor accounting for the consequences of that particular damage on the entire structural system.
The structures analyzed are simply supported multibeam bridges (Figure 1). Typical superstructure cross section configuration of multi-girder bridge steel bridge. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig33_1.tif"/>
The corrective factors found as result of the calibration process lead to values higher than 1.0 whenever the redundancy of a given bridge leads to a structural performance higher than the target. In other words, the structural consequences of member failure are less severe than the consequences of member failure in the bridge used as a base for the calibration. On the other hand, when a bridge presents a system factor smaller than 1.0, it means that the consequence of a member failure in a certain damage state is more severe than in the target bridge. This implementation of system correction factors in bridge condition rating procedures can be of particular interest when trying to manage the rehabilitation of a group of bridges with similar damages but of different structural configurations. In those cases, typical condition rating would rate all bridges with a similar mark. By applying the corrective factors, bridge agencies will be able to give priority to those bridges that present weaker redundancy and robustness characteristics.
