November 22, 2002
Refer to: HSA-10/SS-116
Mr. Mike Chu
Valley Forge & Bolt Manufacturing Co.
1825 South 27th Avenue
Phoenix, Arizona 85009-6417
Dear Mr. Chu:
Thank you for your October 29 letter requesting Federal Highway Administration (FHWA) acceptance of your company=s SPC4tm load indicating fasteners as a component of breakaway slip base sign support systems for use on the National Highway System (NHS). You requested that we find these bolts acceptable for use with slip bases on the 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 slip base sign supports has been conducted 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.
Breakaway slip bases depend upon proper torquing of the bolts to 1) ensure that the bolts will not loosen markedly and fall out due to vibrations and 2) permit the slip base surfaces to move with respect to one another in the event of crash. Your company's specially modified bolts allow a user to check the tension in the bolts once they are installed. This method also provides the opportunity to check the tension after construction to see if the system has "relaxed" to the point where the bolts no longer keep the system stable. Load indicating fasteners can allow a simpler and more accurate periodic inspection.
It is our opinion that the load indicating bolts will perform in an acceptable manner when used in crash-tested slip base systems in lieu of the conventional bolts that are specified. Therefore, the devices described above and shown in the enclosed product literature for reference are acceptable for use as Test Level 3 devices on the NHS under the range of conditions tested, when proposed by a State.
Please note the following standard provisions that apply to FHWA letters of acceptance:
Carol H. Jacoby, P.E.
Director, Office of Safety Design