Federal Highway Administration
1200 New Jersey Ave. S.E.
Washington, D.C. 20590
January 26, 2009
In Reply Refer To: HSSD/SS-159
Mr. Donnie Lewis
Roadway Construction Products, Inc.
3645 Elizabethtown Road
Clarkson, Kentucky 42726
Dear Mr. Lewis:
This letter is in response to your request for the Federal Highway Administration (FHWA) acceptance of omni-directional slip bases for wide flange beams used as sign supports for use on the National Highway System (NHS).
|Name of system:||Roadway Construction Products, Inc. Omni-Directional Slip Base for Wide Flange Beams|
|Type of system:||Sign Support|
|Test Level:||NCHRP Report 350 TL-3|
|Testing conducted by:||Texas Transportation Institute (TTI)|
|Date of request:||October 30, 2008|
You requested that we find this sign support system acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features.”
The FHWA memorandum, “ACTION: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on testing requirements of sign supports and outlines procedures for pendulum testing and estimation of high-speed breakaway performance of sign supports from low-speed pendulum test results.
The two different sizes of posts with the Roadway Construction Products, Inc. Omni-Directional Slip Bases that were tested to evaluate impact performance were the S4x7.7 and the W12x26 posts. Intermediate sizes of posts including S5x10, W6x9, W6x12, W8x18, W8x21, W10x22, and W10x26 were not tested but will be considered for acceptance based on interpolation of the test results. Detailed drawings of the slip base assembly are enclosed.
The S4x7.7 size post was impacted by the pendulum to evaluate omni-directional crashworthy performance. One test was conducted in the strong axis direction and a subsequent test was performed in the weak axis direction. The bolt torque was 37ft/lb at the slip base and 85 ft/lb on the hinge plate for each test.
The W12x26 size post was impacted by the pendulum to evaluate omni-directional performance. One test was conducted in the strong axis and a subsequent test was performed in the weak axis direction. The bolt torque was 62-63 ft/lb at the slip base and 70 ft/lb on the hinge plate for each test.
Test article installations
Each tested post was installed with a surrogate sign attached that represented the largest sign configuration according to the Texas Department of Transportation Standards under a Zone 1 design wind condition. Calculations determined the weight and mounting height of the surrogate sign for each of the post sizes.
The test article installations were tested at the TTI outdoor pendulum testing facility. The pendulum bogie was built according to the specifications of the Federal Outdoor Impact Laboratory's (FOIL) pendulum, and the frontal crush of the aluminum honeycomb nose of the bogie simulated the crush of an actual vehicle. Tests with pendulums are acceptable for most breakaway supports with the exceptions of base bending or yielding supports. Pendulum testing can be used on your company’s sign support systems as a surrogate for a full crash testing.
In each of the four tests, the supports slipped away from the base as designed and came to rest near the impact location. No significant damage was noted to the support or the slip base. Results from testing the Omni-Directional Slip Base show the support slipped away from the base as designed. For the S4x7.7 size post the resulting maximum change in velocity was 1.8 ft/s in the strong axis direction and 1.9 ft/s in the weak axis direction. For the W12x26 size post the resulting maximum change in velocity was 4.5 ft/s in the strong axis direction and 6.0 ft/s in the weak axis direction. In addition, the TTI extrapolated the high speed performance from the low speed pendulum tests. The test articles appear to perform appropriately to make such high speed extrapolations. For the S4x7.7 size post the high speed extrapolations yield acceptable change in velocity values of 3.58 ft/s and 3.29 ft/s respectively in the strong and weak axis direction. For the W12x26 size post the high speed extrapolations yield acceptable change in velocity values of 11.36 ft/s and 12.24 ft/s respectively in the strong and weak axis direction. It is noted that the upper hinge plates did not activate during any of the pendulum tests and this does not result in a failure of the evaluation criteria. A summary of the test results are enclosed.
Based on the test results, the Roadway Construction Products, Inc. Omni-Directional Slip Base for Wide Flange Beams as described above meet the appropriate evaluation criteria for the NCHRP 350 Test Level 3 devices. The beam sizes tested represent the minimum (S4x7.7) and maximum (W12x26) sizes acceptable. Additionally, the post sizes are limited to the conditions and configurations stated in the FHWA’s previous acceptance letters, SS-25 and SS-36, addressing standard I-beam sign support sizes utilizing generic slipbases.
This FHWA acceptance applies to the Roadway Construction Products, Inc. Omni-Directional Slip Base for Wide Flange Beams. These devices may be used at all appropriate locations on the NHS when selected by the contracting authority, and subject to the provisions of Title 23, Code of Federal Regulations, Section 635.411, as they pertain to proprietary products. This acceptance is based on the reported crash performance of your device and is not meant to address the limitations of testing or the systems’ installation, maintenance, or repair characteristics.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
David A. Nicol
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