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Characteristics of Decommissioned Bridges

Description:

Bridge preservation activities have focused on the service life extension of bridge components or protection systems that extend the life of bridge as a whole. National efforts are underway to look at materials, design and construction practices to extend the useful life bridges toward an elusive 100 year mark. Informal research done by the Transportation Research Board Bridge Preservation Committee (AHD037) using 20 years of National Bridge Inventory data for all states in the United States indicates that the majority of bridge replacements are not driven by the condition of the bridge. Additional evaluation of the causes of bridge replacements in California has found similar results to the national findings.

If the majority of bridges are not being replaced due to condition, then what is driving bridges to be taken out of service? Are bridge preservation efforts appropriately focused on the true factors that are leading to the premature replacement of bridges? Understanding what is causing bridges to be decommissioned will allow bridge managers to better adapt practices to achieve the maximum possible service life.

Objective:

The initial research activity will mine many years of National Bridge Inventory (NBI) data to characterize various attributes of bridges in their last year of NBI reporting prior to being decommissioned.

The study seeks indicators of causes of decommissioning. The causes can include:

·

Deterioration, indicated by general condition ratings

·

Constraint to mobility, indicated by number of lanes on/under structure, and load ratings

·

Vulnerability, indicated by ratings for scour critical bridge item, and critical feature items

·

Geometric constraints, indicated by deck width, and vertical clearances

Decisions to replace/retain bridges may be found to depend on relations of NBI items to route functional class, ADT, and ADTT. For decommissioned bridges, the study will examine the importance of individual NBI items and cross-correlations among NBI items. Quantification of the average life span of bridges by material, design type, geographic area and environment will be determined. Armed with the results of the national analysis, the research will evaluate more definitively the cause of replacements for three or four selected States using Department of Transportation project information.

Benefits:

The management of the aging bridge population in the United States is a multi-billion dollar public liability.

National focus in the areas of bridge preservation has been geared toward condition extension methods. These conditioned focused efforts are important, but if bridges are found to be replaced for reasons other than condition, then bridge managers should focus additional research, practice, and policy on addressing these issues. Research that clearly identifies what drivers we are trying to preserve for holds the potential to extend the service lives of bridges and save billions of taxpayer dollars.

Related Research:

No previous published research could be found evaluating the causes of decommissioned bridges. Published research is available that investigates the causes of bridge collapses may inform this effort, but is not focused on bridges removed from service in non-catastrophic ways.

One research report titled, “The Need for Conducting Forensic Analysis of Decommissioned Bridges”[1] recognizes the need for a broad study similar to the one proposed in this needs statement. This research found that over 30% of decommissioned bridges had no condition deficiencies support the premise of this proposed research.

One unpublished study examined NBI data of bridges that were replaced[2]. Additionally, The California Department of Transportation has evaluated the cause of bridge replacements over a 10 year period has been published in presentation form only.


[1] Chase,S.B.(2012). The Need for Conducting Forensic Analysis of Decommissioned Bridges. UVA-2012-05, 36p.

[2] Hooks,J.M (2011). Structural and Functional Characteristics of Decommissioned Bridges. Proc. National Bridge Management, Inspection and Preservation Conference, Proctor, Varma, Hooks, eds.

Tasks:

This research consists of a number of related tasks to help ascertain the driving causes of bridge decommissioning in the United States. Specific tasks include:

  1. Perform a synthesis of similar and related research on the topic of causes of decommissioning of bridges.

  2. 2.

Conduct a survey of State DOT’s to capture the policies and justifications for replacement of bridges. This survey should related condition, performance, vulnerabilities and functional replacement justifications to associated NBI data.

  1. Utilize nationwide National Bridge Inventory databases to analyze the characteristics of bridges in their last year in the inventory prior to decommissioning. Determine the expected service life of bridges based on material, design types, traffic volumes, truck volumes, geography, environmental conditions, functional classifications, and others. For bridges that are not structurally deficient at the time of decommissioning, determine the probable cause of the replacement by looking at alternative drivers, including by not limited to scour vulnerabilities, load capacities, vertical and horizontal clearances, and adequacy of service (level of service) of the roadway carried on the bridge.

  2. 4.

Utilize the results from task 2 to select three to four State Departments of Transportation where project level records exist to positively confirm the characteristic drivers for bridge replacement. This task will involve a review of agencies replacements and project records to determine the causes of replacements. The state level results should be correlated to the national level results.

  1. Summarize the findings from both national and state level reviews and recommend needed research areas to help achieve extended bridge service lives.

Implementation:

The results from this research will be of immediate use for the determination of realistic service lives of bridges to be used in life cycle cost analysis. Causes of replacement other than condition related may justify additional research in those areas to help achieve a greater bridge service life. Strategies to design and construct bridges that are adaptable to changing functional needs over time may result in improved practices. The American association of State Highway and Transportation Officials is in the process of developing a “Bridge Preservation Best Practices Manual” that would provide an avenue for findings to immediately impact bridge practitioners. **

Relevance:

Having a clear understanding of what is really driving bridge replacements will guide bridge preservation efforts to include methods to extend the life span of bridges that are not entirely focused on condition. If bridge preservation efforts are targeted towards replacement drivers beyond condition, a hundred-year service life for bridges may become a commonplace.

Sponsoring Committee:AHD37, Bridge Preservation
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Michael B. Johnson, Jeff Weidner, Reed Ellis
Source Info:[1] Chase,S.B.(2012). _The Need for Conducting Forensic Analysis of Decommissioned Bridges_. UVA-2012-05, 36p.
[2] Hooks,J.M (2011). _Structural and Functional Characteristics of Decommissioned Bridges_. Proc. National Bridge Management, Inspection and Preservation Conference, Proctor, Varma, Hooks, eds.
Date Posted:05/10/2016
Date Modified:06/17/2016
Index Terms:Maintenance practices, Preservation, Service life, Bridge construction, Bridge design, National Bridge Inventory, California, Replacement (Bridges),
Cosponsoring Committees: 
Subjects    
Highways
Maintenance and Preservation
Bridges and other structures

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