February 8, 2005
Refer to: HSA-10/LS-58
Mr. Bob Sik
Akron Foundry Company
2728 Wingate Avenue
P.O. Box 27028
Akron, Ohio 44319-0009
Dear Mr. Sik:
Thank you for your January 6 letter sent via email requesting Federal Highway Administration (FHWA) acceptance of a modification to the installation of your company's cast aluminum transformer bases. You requested that we find the use of "stack pack" rectangular washers with these bases acceptable for use on the National Highway System (NHS) under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features."
Testing of the supports was in compliance with the guidelines contained in the NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. Requirements for breakaway supports are those in the American Association of State Highway and Transportation Officials' (AASHTO) Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals.
Full-scale automobile testing and pendulum testing has been conducted on your company's cast aluminum bases resulting in a number of the FHWA acceptance letters being written. You noted that some installers have been placing your bases on smaller bolt circles than they have been designed for. Using conventional round washers does not provide enough contact between the anchor bolts and the tabs on the bottom of the casting. The purpose of the rectangular washers is to better distribute the loading from the pole to the foundation. We concur in your assertion that the use of smaller diameter bolt circles with the stack pack washers used to distribute the load will not have an adverse affect on the breakaway performance of these transformer bases. However, the washers should not be used to distribute the loading outside of diameter of the largest bolt circle they were tested with.
The modifications to the installation details of your cast aluminum transformer bases, as described above, are acceptable for use as Test Level 3 devices on the NHS under the range of conditions tested, with the exception of the use of a smaller bolt circle diameter, when proposed by a State.
Please note the following standard provisions, which apply to the FHWA letters of acceptance:
/Original Signed by Harry W. Taylor/
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety