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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-200

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U.S. Department of Transportation
Federal Highway Administration

1200 New Jersey Ave. S.E.
Washington, D.C. 20590

January 28, 2010

In Reply Refer To: HSSD/B-200

Mr. Ronald K. Faller, Ph.D.
Research Assistant Professor
Midwest Roadside Safety Facility
University of Nebraska-Lincoln
527 Nebraska Hall
Lincoln, NE 68588-0529

Dear Dr. Faller:

This letter is in response to your request for the Federal Highway Administration (FHWA) acceptance of a roadside safety device for use on the National Highway System (NHS).

Name of device: West Virginia Steel Bridge Railing for use on Transverse,
Nail-Laminated, Timber Bridges
Type of device: Permanent Steel Barrier
Test Level: NCHRP Report 350 TL-2
Testing conducted by: Midwest Roadside Safety Facility (MwRSF)
Date of request: September 13, 2009
Date of completed package: September 13, 2009
Task Force 13 Designator: SBT11b

You requested that we find this device 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 devices should meet the guidelines contained in the NCHRP Report 350 or the American Association of State Highway and Transportation Officials’ Manual for Assessing Safety Hardware (MASH). The FHWA Memorandum “Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Description
For this project, the research objectives included the modification of existing test level 2 (TL-2) steel thrie beam bridge railing as per FHWA Acceptance Letter HSA-10/B-138 dated August 4, 2005. This thrie beam steel post bridge barrier was connected to a transverse, glue-laminated, timber bridge deck system. Eight 7/8-in. (22.2-mm) diameter by 7 3/4-in. (197-mm) long, ASTM A307 (Grade 2 equivalent) hex head bolts with timber shear connectors were used to anchor the posts and deck plates to the glulam timber deck panels. For this research, crash testing used the same barrier and connection plate system for use on a transverse, nail laminated, timber bridge deck supported by steel wide-flange beams. The Steel Bridge Railing for use on Transverse, Nail-Laminated Timber Bridge Decks was evaluated using dynamic bogie testing on the steel bridge posts attached to nail-laminated timber deck. The dynamic component testing program was then used to verify that the post-to-deck attachment hardware as well as the timber deck would remain intact under peak impact loading deemed representative of a pickup truck crash test conducted under the TL-2 impact safety standards of NCHRP Report 350. In addition, the testing was used to demonstrate that the peak impact loading would not result in significant deck damage. Dynamic component testing was used to verify use of the previously crash-tested bridge railing system on transverse, nail-laminated, timber deck bridges. In addition, testing also evaluated the benefits for utilizing timber shear plates within the post-to-deck connection.

The steel bridge posts were 42 3/4-in. (1,086-mm) long, W6x12 (W152x17.9) beams made from ASTM A992 or ASTM A572 Grade 50 steel, as shown in Figures 7 through 9. Near the top of the post, four 3/4-in. (19-mm) diameter bolt holes were placed within the front flange. The blockouts were bolted to the posts using these bolt holes. Slots were cut into the front flange near the bottom of each post and used to fasten the bottom deck plate to the post.

In addition to the fabricated holes and slots, a steel post plate was welded to the front flange 9 in. (229 mm) from the bottom of the post. Each post plate measured 10 3/8 in. x 4 in. x 1/2 in. (264 mm x 102 mm x 13 mm). Two slots were cut into the post plate and used to bolt the top deck plate to the post. To provide stiffness and resistance to buckling, gusset plates and stiffeners were also welded to the posts.

Gussets were placed on both sides of the web at the bottom of the post and directly behind the top of the post plate, while the post wing stiffeners were located along the top of the post plate and adjacent to the gusset plates. These gussets and stiffeners were designed to provide additional stiffness to the post and to prevent localized buckling near the deck plate attachments.

Deck plate assemblies were utilized to attach the bridge posts to the bridge deck. The top deck plate was 1/2 in. (13 mm) thick, while the bottom deck plate was 3/8 in. (10 mm) thick. The deck plates are fabricated from ASTM A36 steel and contained eight 1-in. (25-mm) diameter holes. Eight 7/8-in. (22.2-mm) diameter by 7 3/4-in. (197-mm) long, Grade 5 bolts were to be used to fasten the deck plates to the edge of the timber bridge deck. Since this detail produced minor bearing deformations around some of the vertical holes, the following alternative attachment options to reduce the incidence of deformations may be specified:

  1. Eight 7/8-in. (22.2-mm) diameter ASTM A307 (Grade 2 equivalent) bolts in combination with 4-in. (102-mm) diameter timber shear connectors.
  2. Eight 7/8-in. (22.2-mm) diameter ASTM A325 (Grade 5 equivalent) bolts in combination with 4-in. (102-mm) diameter timber shear connectors

Steel rectangular end plates were welded to the back side of the deck plates and provided the locations where the bridge post bolted to the plates. The end plates were welded to the deck plates using triangular-shaped plate stiffeners. Two 7/8-in. (22.2-mm) diameter ASTM A325 hex head bolts were used to fasten the top deck plate to each post, while two 5/8-in. (15.9-mm) diameter ASTM A325 hex head bolts were used to fasten the bottom deck plate to each post.

Post blockouts were configured with ASTM A992 or ASTM A572 Grade 50, W6x12 (W152x17.9) steel sections that attached to the front face of the bridge posts. Eight 3/4-in. (19-mm) holes, four in the front flange and four in the back flange, were placed into each blockout. Four 5/8-in. (15.9-mm) diameter by 2-in. (51-mm) long, ASTM A307 heavy hex head bolts were used to secure each blockout to each post.

A transverse, nail-laminated, timber bridge deck was constructed at MwRSF's outdoor test facility for this research project. The bridge deck was constructed from 14-ft (4.3-m) long, 2-in. x 6-in. (51-mm x 152-mm) treated, dimensional lumber and covered by a 2-in. (51-mm) thick concrete wearing surface. The timber boards were manufactured from Grade No. 1 Southern Yellow Pine and treated with ACQ-D to a minimum net retention of 0.40 lbs/ ft3 (6.41 kg/m3) satisfying AWPA U1, UC4A. However for actual bridge installations, the research recommends that the dimensional lumber boards be treated to a net retention of 0.60 lbs/ft3 (9.61 kg/m3) satisfying AWPA U1, UC4B. The boards were placed on end and nailed together through and perpendicular to the wide face of the board using 20d or 20 penny "common" nails. A specific nail pattern, which repeated every four boards, was used to ensure that a nail did not contact a previously driven nail. Special care was given to the nail pattern near the deck edge to ensure the nails did not occupy space where the vertical bolt holes for the bridge rail would later be drilled. During deck assembly, two beads of Liquid Nails Heavy Duty Construction Adhesive were applied to the sides of the boards and over the outer 3 ft (0.9 m) of deck. The adhesive was used to provide additional punching shear resistance in the deck as well as improved load transfer between boards.

West Virginia TL-2 Steel Bridge Railing for use on Transverse Nail-Laminated, Timber Bridge Barrier drawings for the construction of the test installation are included with this correspondence. In addition, transition details for this bridge barrier can also be found in FHWA Acceptance Letter HSA-10/B-138 Revised.

Findings
We concur with your request that the West Virginia Steel Bridge Railing for use on Transverse Nail-Laminated, Timber Bridges be granted equivalence to existing successfully crash tested bridge rail meeting TL-2 conditions as per NCHRP Report 350 and will be considered acceptable for use on the NHS. For further information on the crash test, the Test Data Summary Sheet is included with this correspondence.

Please note the following standard provisions that apply to the FHWA letters of acceptance:

 

Sincerely yours,

Signature of David A. Nicol

David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety

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