U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Ave. S.E.
Washington, D.C. 20590
August 3, 2009
In Reply Refer To: HSSD/B-186
Mr. Rick Mauer
Outside National Sales Representative
Nucor Steel Marion Inc.
P.O. Box 837
Greenland, NH 03840
Dear Mr. Mauer:
This letter is in response to your request for the Federal Highway Administration's (FHWA) acceptance of a modification to a Nucor Steel Marion W-beam barrier for use on the National Highway System (NHS).
| Name of system: | Nu-Guard 27 Barrier System posts mixed with Standard “Strong Post” guardrail |
|---|---|
| Type of system: | W-beam guardrail |
| Test Level: | NCHRP Report 350 Test Level-3 (TL-3) |
| Testing conducted by: | Holmes Solutions of New Zealand |
| Date of request: | June 29, 2009 |
You requested that we find this modified system acceptable for use 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.”
Requirements
Roadside safety systems should meet the guidelines contained in the NCHRP Report 350. FHWA Memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.
Description
The TL-3 Nu-Guard barrier system consists of Nucor Strong Posts which are hot rolled, high tensile steel fabricated into a U cross section of approximately 2 in deep and 3 1/2 in wide. The weight of each post is 5 pounds per foot. A slot, ¾-in wide is located 1 in down from the top of the posts in the middle of the cross section. The slot has a total length of 7 in. All posts are 78 in long and are hot dip galvanized. When Nucor posts are used with 27-in high non-proprietary W-beam guardrail systems, they are used with the original plastic blockouts measuring 14 in x 3/8 in which are used to space the guardrail 8 in from the face of the U posts. The plastic blockouts are manufactured from a 50 percent blend of new and recycled high density polyethylene (HDPE).
This system was originally found acceptable in the following FHWA Acceptance Letter:
Your present request is for the TL-3 Nu-Guard 27 w-beam barrier system with blockouts to be accepted for use when maintaining standard strong-post w-beam guardrail. The dynamic deflection during the Nu-Guard 27 Test 3-11 was approximately 3 ft, 6 in., which is slightly greater than the 3 foot deflection normally seen with strong post W-beam systems. This indicated that barrier using the Nu-Guard posts performs in a similar manner to conventional strong-post W-beam. It was determined that a developmental test would be conducted to validate this assumption when replacing standard posts with Nu-Guard posts.
Crash Testing
To confirm that Nu-Guard posts could be substituted for W6 x 9 steel posts in conventional “strong post” W-beam guardrail a single developmental test was conducted. A 175-foot long section of W-beam guardrail was constructed with standard W6 x 9 posts spaced at 6 feet, 3 inches. Three posts at the impact site were replaced with Nucor Marion Steel Nu-Guard posts.
The vehicle used as a surrogate for the Chevy 2500 was a Mazda Proceed which was readily available in New Zealand and has comparable weight and measurements. Although this vehicle was not a pickup truck, it had similar measurements in terms of fender height and center of gravity but with a narrower and shorter wheel base. This in effect makes the vehicle less stable than the Chevy 2500 but still results in a test that is a good representation of what one would expect should the impacting vehicle be a Chevy 2500. The vehicle had a curb weight of 1845 kg and was ballasted to 2000 kg.
The vehicle impacted the barrier at a nominal speed of 100 km/hr and at an angle of 25 degrees. Initial contact was made mid-span between posts 8 and 9, 9 being the first Nu-Guard post and splice joint. Redirection, or the point at which the vehicle was parallel with the rail, was reached at approximately the point at which the front left wheel of the vehicle reached post 11 (the third and last Nu Guard post). The vehicle then began exiting the system, fully engaging post 12 (the first I beam post downstream) and post 13 upon exit. The left front wheel was dislodged from the vehicle by post 13 and the vehicle then exited the system, coming to rest approximately 30 meters downstream from the impact point and within one vehicle width of the barrier.
The test data summary sheet and a drawing of the test installation are enclosed for reference.
We concur that a test with the 820C vehicle is not necessary as barrier deflection with the small car would be less than with the Mazda Proceed. Also, the 820C vehicle would not tend to snag on the blocked-out Nu-Guard posts any more than standard W6 x 9 posts. Therefore, Nucor-Marion Steel Nu-Guard U-channel posts may be used in lieu of W6 x 9 posts when maintaining W-beam guardrails. Because 6-in by 8-in wood guardrail posts are generally considered interchangeable with W6 x 9 steel posts under NCHRP Report 350 conditions, the Nu-Guard U-channel posts may also be used when repairing wood post systems of comparable heights.
Please note the following standard provisions that apply to FHWA letters of acceptance:
Sincerely yours,
David A. Nicol, P.E. |
