October 7, 1997
Refer to: HNG-14/SS-68B
Mr. Lawrence E. Leahy
P.O. Box 135
Auburn, IL 62615
Dear Mr. Leahy:
This is in response to your August 8 letter to Mr. Nicholas Artimovich requesting
that your company's Xcessories Squared slip-base components be found acceptable
when used with an existing three-bolt triangular slip base anchor plate.
Our acceptance letter SS-68, dated September 18, 1996, found your company's
slip base acceptable for use on the National Highway System (NHS) when used
with a single 63.5 mm square, 12 gage perforated steel tube sign support and
a foundation tube with a soil plate or a concrete foundation.
We concur with your assessment that the components of the system can be expect
to perform in an acceptable manner when used with an existing compatible triangular
slip base. Therefore, they will e acceptable for use on existing foundation
slip plates on the NHS, subject to the following conditions.
- The foundation slip plate and the support mass are similar to those crash
tested. (A drawing of the tested system is enclosed for reference. Critical
components of crashworthy slip bases are the clamping force in the splice
bolts, the size (angle) of the notch to receive the splice bolts, the thickness
and material properties of the slip plates, and the finish of the surfaces,
both those of the throats of the notches and those of the parallel slip
surfaces. Care must be exercised to ensure that Xcessories Squared components
used with an existing foundation slip plate are compatible and create a
slip base comparable to that tested.)
- The foundation anchor is at least as firm as the crash-tested installation
covered in our acceptance letter SS-68. (In that installation the stub in
strong soil was affixed with a soil plate, as in the enclosure. Your standard
concrete foundation would, of course, also be acceptable.
- All hardware in the slip base except the foundation slip plate is replaced
by the Xcessories Squared hardware kit, including a Teflon bolt retainer
gasket and two stainless steel release bushings on each splice bolt.
Should you have any questions, please do not hesitate to call Mr. Artimovich
at (202) 366-1331.
Dwight A. Horne, Chief
Federal-Aid and Design Division
Supplemental Geometric and Roadside Design Acceptance Letter SS-68B
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