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Development of a Flexible Bridge Railing for Longitudinal Timber Decks




Ronald Faller, Barry Rosson




A low-cost, flexible W-beam bridge railing with "breakaway" posts was developed for use on longitudinal timber deck bridges located on low-volume roads. The bridge rail consisted of a 12-gauge (2.66-mm) W-beam rail supported by 3.5-in. by 5.5-in. (89-mm by 140-mm) dressed lumber posts spaced 6-ft 3-in. (1,905-mm) on center. Each post was placed between two 5-in. by 5-in. x 3/8-in. (127-mm x 127-mm x 9.5-mm) steel angles and connected to the vertical edge of the bridge deck with two 3/4-in. (19.0-mm) diameter by 12.0-in. (305-mm) long lag screws. The research study included 37 static component tests, computer simulation modeling with BARRIER VII, and two full-scale vehicle crash tests using 3/4-ton pickup trucks. The first crash test, impacting at a speed of 31.2 mph (50.2 km/hr) and at an angle of 26.8 degrees, was unsuccessful because the vehicle vaulted over the bridge rail using a 24-in. (610-mm) top mounting height. Consequently, the height of the railing was increased to 27.78 in. (706 mm), resulting in a successful crash test at a speed of 30.6 mph (49.2 km/hr) and at an angle of 24.9 degrees. The safety performance of the bridge railing was determined to be acceptable according to the Test Level 1 (TL-1) evaluation criteria described in the National Cooperative Highway Research Report No. 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features.


Highway Safety, Roadside Safety, Guardrail, W-beam, Longitudinal Timber Deck, Bridge Railing, NCHRP-350, Low-volume, Computer simulation, Crash test, TL-1

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