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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

 
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Publication Number:  FHWA-HRT-15-081    Date:  May 2016
Publication Number: FHWA-HRT-15-081
Date: May 2016

 

Synthesis of National and International Methodologies Used for Bridge Health Indices

Chapter 7. Conclusions

This synthesis discussed state-of-the-art bridge condition or health indices being used to assess performance of bridges in the United States and other countries. Current methods for developing condition or health indices were grouped into four different approaches based on the computational methods used. A discussion on each approach covered the data required for computing the index and the strengths and limitations of the approach.

The majority of health indices are designed to help stakeholders plan for bridge maintenance and rehabilitation activities. This is typical among weighted averaging and ratio-based approaches, which calculate the overall health index by combining all defects identified at the element level. Other health indices, such as the worst-conditioned component index, are more interested in identifying weak links within the bridge structure that could severely affect the safety and durability of the bridge in case of a disaster. They are frequently used together with weighted averaging methods. Most systems rely on a qualitative approach to assess bridge health and performance. Qualitative methods are essential for general assessment of the bridge condition and identifying bridges that need maintenance.

With the exception of the recently supplanted SR, all other BMSs rely on element-level inspection data to obtain the overall BHI. The use of element-level inspection data provides a more thorough assessment of the condition of the bridge. It also provides a more objective evaluation of the bridge’s condition because it reduces reliance on inspector’s judgment for rating the condition of the bridge. Element-level inspection enables inspectors to capture both the severity and extent of any problems that may influence the integrity of the structure. Such information is valuable for planning maintenance, repair, and rehabilitation programs.

A key recurring limitation identified is the lack of accurate and objective data used to compute the condition indices. Visual inspection remains the predominant approach for assessing the condition of bridge elements. Since this heavily relies on human judgment, the possibility of one inspector rating the condition state of an element differently from another inspector is likely. Therefore, a true assessment of the condition of bridge elements is difficult and uncertain since the data acquired is sensitive to the inspector’s expertise and sound judgment. The use of expert opinion and engineering judgment, as reflected in assigning weights and defining the relative importance of an instance of damage or an element, plays a key role in the estimation of condition indices. Opinions about the criticality of an instance of damage or a bridge element to the overall structure is highly variable. Using engineering judgment alone may introduce subjectivities into the estimation. Therefore, it is safe to conclude that with the current visual inspection approach to acquiring bridge condition data, the possibility of subjective and imprecise data entering the estimating process is present. The development of condition indices should be driven by more objective and quantitative data, which will help bridge managers make data-driven decisions.

Studying the basis for the BHIs used around the world also shows that most indices do not consider operational, safety, and lifecycle cost performance metrics and mostly rely on condition states of the bridge’s elements or components. It is important that an effective performance-based health index includes metrics at different limit states such as utility, operations, serviceability, structural, maintenance, safety, resilience, traffic, financial, and environmental.

It should be noted that subjectivity in BHIs will never diminish because some qualitative performance metrics always require some level of engineering judgment or input, such as condition ratings assignments to bridge elements. Currently, FHWA is establishing research-oriented protocols for data collection during bridge assessment, inspection, NDE, and
field testing. These protocols could be leveraged in reducing subjectivity when assigning qualitative metrics.

 

 

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