May 26, 2005
In Reply Refer To: HSA-10/B-82C
Mr. Derek W. Muir
Group Managing Director
Hill & Smith Ltd.
Springvale Business and Industrial Park
Bilston, Wolverhampton, West Midlands, WV14 0QL
Dear Mr. Muir:
In your May 10 letter, you requested formal Federal Highway Administration acceptance of a three-cable version of your originally-accepted 4-strand Brifen Wire Rope Safety Fence (WRSF) as an National Cooperative Highway Research Program (NCHRP) Report 350 test level 3 (TL-3) traffic barrier. To support this request, you submitted a report entitled “Full-scale Crash Evaluation of a Wire Rope Safety Fence, NCHRP Report 350, Tests 3-10, 3-11, and 3-35, SwRI Test Nos. B-USA-C1, B-USA-C2, B-USA-C3, and B-USA-C4.” This report detailed the four tests conducted by personnel from the Southwest Research Institute using a temporary site in Ardmore, Oklahoma. The test installation was 278-m long, including the anchors at each end. These anchors were the same design that was tested and accepted for the 4-cable barrier, but only three of the four cable slots were used in the 3-cable design. Rope tension was adjusted according to your specifications for the ambient temperatures immediately preceding each test and averaged 24-kN.
The three-cable TL-3 Brifen design consists of three separate cables, the bottom two of which are interwoven between posts. As with your 4-rope design, the top cable is set in a 101-mm deep x 22-mm wide slot cut into the top of each post. Cable heights measured from ground level are 460 mm, 600 mm, and 720 mm, respectively. The posts are S-shape posts, 100-mm x 55-mm x 4.55-mm thick, manufactured from ASTM A36 steel that is galvanized after fabrication. These details are shown in Enclosure 1. Standard post spacing is 3.2-m and was used in test C2. A 2.4-m spacing was used in test C3. For all tests, 1220-mm long posts were set 408 mm into tubular steel sockets contained in 305-mm diameter concrete footings 760-mm deep. The alternate designs accepted for the 4-cable system, i.e., driven posts or posts set in driven steel sleeves, may also be used with the 3-cable design.
A summary sheet for the four tests you conducted is shown in enclosure 2. When comparing dynamic deflections in tests C2 and C3, I noted that the reported dynamic deflection was predictably greater in both tests than the 2.4 m deflection noted in the 4-cable design, but that the 3-cable deflection was actually somewhat greater with the closer post spacing. This emphasizes the fact that the design deflections for all flexible and semi-rigid barriers are approximations, usually based on a single test. As such, they should be used as guidelines for barrier design and placement rather than precise distances that will never vary. Test C4 was essentially a terminal test, intended to establish the barrier beginning length of need point and to verify the structural adequacy of the anchor. For the 3-cable system, the length of need point was determined to be the same as it was with the 4-cable design, beginning approximately 9.3 m from the anchor point, between the last anchor post and the first line post (post 5).
In summary, your Brifen 3-cable WRSF, as described above, remains acceptable as a TL-3 traffic barrier and may be used on the National Highway System when such use is specified by the contracting agency. I understand that all steel components used in any of the accepted Brifen systems are manufactured in the United States (U.S.) with U.S. steel and are not subject the Buy America provisions of Title 23, U.S. Code (USC), Section 635.410. However, your barrier designs are proprietary and, as such, their use on Federally-funded projects remains subject to the conditions listed in Title 23 USC, Section 635.411.
/original signed by/
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety