September 5, 2002
Phil TenHulzen, P.E.
Standard Plans Engineer
Nebraska Department of Roads
PO Box 94759
Lincoln, NE 68509-4759
Dear Mr. TenHulzen:
In response to your e-mail request last May, please be advised that the Nebraska Bridge Approach Section described in the Texas Transportation Institute's report entitled “NCHRP Report 350 Test 3-21 of the Nebraska Thrie-Beam Transition” may be considered a test level 3 (TL-3) transition design and used on the National Highway System when such use is acceptable to the contracting agency.
Your non-proprietary design consists of 3810 mm of nested 12-gauge Thrie-beam supported on two W150 x 37 x 2591-mm long steel posts, followed by four 150W x 22 x 2134-mm long steel posts. The first post from the bridge is 1220 mm from the concrete parapet and the next four posts are on 952-mm centers. A similar design using 250 x 250 x 2591-mm long wood posts and 200 x 200 x 2135-mm long wood posts for their steel post counterparts is also acceptable. A TS 102 x 102 x 7.9 steel tube spans the gap between the bridge end and the first post and connects to each with special steel brackets. This tube is used to support a wood offset block centered approximately 300 mm from the end of the concrete parapet. These and other details are included in the enclosed test report.
The enclosed test report indicates that a “pipe spacer” between the concrete parapet and the nested Thrie-beam elements was crushed 25 mm in the test. As can be seen in the photographs, and as you later verified, your design does not incorporate a spacer. However, the end of the parapet was damaged in the crash and there was significant snagging on the concrete underneath the Thrie-beam rail. Nevertheless, all Report 350 evaluation criteria were met as noted on the test results summary sheet included in the report.
I understand that CAD drawings of this design are available through your office upon request and that you can be contacted directly via e-mail at firstname.lastname@example.org.
(original signed by Carol H. Jacoby)
Carol H. Jacoby, P.E.
Director, Office of safety design