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Thrie Beam Blockouts

Question
State WI
Description Text  We would like some guidance on the appropriate blockout to use for a standard thrie beam, both for wood posts and steel posts.


WisDOT is working on developing a thrie beam bullnose terminal based on the MwRSF design(report TRP-03-95-00, 6-1-2000) that was approved by FHWA (11-8-2000 letter, HSA-1/HSA-cc68). The blockout for the standard thrie beam construction from posts 9 to 12 is shown as 360 mm (14.17 in) high.


Sheet 2 of Minnesota DOT's Standard No. 5-297.611 "Thrie Beam Bullnose Guardrail for Medians" (dated 8-20-2001), which is based on the approved MwSRF design uses a 22-inch high blockout.
 
Keywords
  • Guardrail
Other Keywords none
Date May 10, 2006


Response
Response

Per your inquiry, I have summarized several of the successful thrie beam transition tests that have been conducted according to the NCHRP Report No.

350 requirements. They are as follows:

 

No. 1 - Wood Post - Wood Blockout

            550 mm center rail height

            804 mm top rail height

            150 mm by 200 mm by 554 mm blockouts

            150 mm by 200 mm by 1.9 m posts

            0.68 m dynamic deflection

            TL-3 pickup truck test (404211-11)

 

No. 2 - Steel Post - Modified Steel Blockout

            610 mm center rail height

            864 mm top rail height

            W360x33 tapered blockouts

            W150 x14 posts

            0.71 m dynamic deflection

            TL-4 single-unit truck test (404211-5a)

 

            610 mm center rail height

            864 mm top rail height

            M14x18 tapered blockouts

            W6 x9 posts

            1.02 m dynamic deflection

            TL-3 pickup truck test (471470-30)

 

No. 3 - Steel Posts - Routed Wood Blockout

            550 mm center rail height

            804 mm top rail height

            150 mm by 200 mm by 554 mm routed blockouts

            W150 x14 posts

            0.58 m dynamic deflection

            TL-3 pickup truck test (404211-10)

 

In summary, you can use either the long wood blocks, shortened wood blocks, or even the tapered steel blocks in combination with the standard thrie beam guardrail systems after post no. 9.
Date May 15, 2006


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