U.S. Department of Transportation
Federal Highway Administration
|Subject:||Information: Additional Guidance for Assessment of Bridges Over Waterways with Unknown Foundations||Date:||October 29, 2009|
|From:||/ Original Signed by
From: M. Myint Lwin, P.E., S.E.
Director, Office of Bridge Technology
|To:||Associate Administrator for RD&T
Associate Administrator for Federal Lands Highway Program
Directors of Field Services
Director of Technical Services
This memorandum presents technical guidance on conducting risk-based assessments for bridges over waterways with unknown foundations. Attachment "A" provides an example procedure for categorizing bridges and conducting assessments. Please note that this is one example. Several bridge owners are using other acceptable methods to assess bridges with unknown foundations. This guidance is meant to support ongoing efforts and not to supersede them.
Bridges with unknown foundations represent a subset of bridges over waterways that have not been evaluated for scour. This definition was clarified in our June 3, 2009, memorandum to ensure that bridge owners clearly understand the issue as it relates to the scour program. The unknown foundations team members defined an approach for addressing this subset of bridges that:
- Assists owners in developing and implementing risk-based procedures to determine enough about a bridges foundations to conduct a scour evaluation;
- Moves the bridge into the scour program for evaluation if the owner is comfortable with the risk-based assessment of the bridge foundations (this is the equivalent of recoding the bridge to a 6);
- Recodes the bridge accordingly after evaluation for scour vulnerability.
The goal of this approach is to reduce, not eliminate the inventory of bridges coded U in Item 113 of Recording and Coding Guide for the Structure Inventory and Appraisal for the Nations Bridges (Coding Guide). There will be an inventory of bridges that remain coded U because sufficient information could not be obtained to advise recoding. The guidance herein, and appended, offers a rational approach to determining enough about a bridges foundation to conduct a scour evaluation or appropriately address bridges that will remain coded U.
For bridges that will remain coded U, owners should develop and implement a plan of action (POA), until properly designed countermeasures are installed to protect the bridge foundations or until the bridge is replaced. Attachment "B" provides guidance on developing POAs for bridges that will remain coded U in Item 113.
The team is currently developing Web-based and instructor led training to assist owners with some of the more difficult aspects of the unknown foundations initiative. Specifically, we will be focusing assistance on grouping and categorizing bridges, defining the risk for these owner defined groups, and developing and implementing POAs for bridges remaining with code U in Item 113.
This memorandum with the attachments will be posted on the unknown foundations Website. All information related to the unknown foundations initiative is housed at this location. It can be accessed at https://www.fhwa.dot.gov/unknownfoundations/. If you have any questions, please contact Mr. Silas C. Nichols at (202) 366-1554.