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MGS Transition Blockouts

Question
State	MI
Description Text	I have one more question regarding the guardrail transition that MwRSF tested. In Michigan we use 31” tall w-beam guardrail with 8” offset blocks, so we would be interested in using transitions constructed entirely with 8” deep offset blocks. Would it be acceptable to use 8” offset blocks in lieu of 12” offset blocks on the posts identified below? Thanks again.

System Performance Evaluation

System Types
Approach Guardrail Transitions (AGTs)

Applications

System Features

Date February 21, 2019
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Attachment MI_Transition.jpg

Response
Response (active)	We have addressed similar questions from states previously. Full-scale testing of the upstream stiffness transition with 12in. deep blockouts resulted in significant vehicle snagging on the posts. The small car impacts snagged enough that the vehicles never reached parallel, and instead, they yawed back into the guardrail as they were being contained. This happened in both the curb and non-curbed test installations. Thus, we have concerns that reducing the blockout depth from 12” to 8” would increase the amount of vehicle snag in the upstream stiffness transition and may lead to vehicle instabilities and/or excessive decelerations. Thus, we have recommended that the blockouts in the upstream stiffness transition remain at 12” until further evaluation is completed. This includes all standard 6-ft W6x8.5 posts at ½ or ¼ post spacing. I also wanted to note that the drawing supplied shows the original upstream stiffness transition which utilized W6x12 posts. We have developed a simplified version incorporating only 6-ft long W6x8.5 posts that you may wish to consider. https://mwrsf.unl.edu/researchhub/files/Report38/TRP-03-210-10.pdf https://mwrsf.unl.edu/researchhub/files/Report32/TRP-03-243-11.pdf https://mwrsf.unl.edu/researchhub/files/Report295/TRP-03-291-14.pdf Thanks

Response

Response
(active)

We have addressed similar questions from states previously.

Full-scale testing of the upstream stiffness transition with 12in. deep blockouts resulted in significant vehicle snagging on the posts. The small car impacts snagged enough that the vehicles never reached parallel, and instead, they yawed back into the guardrail as they were being contained. This happened in both the curb and non-curbed test installations. Thus, we have concerns that reducing the blockout depth from 12” to 8” would increase the amount of vehicle snag in the upstream stiffness transition and may lead to vehicle instabilities and/or excessive decelerations. Thus, we have recommended that the blockouts in the upstream stiffness transition remain at 12” until further evaluation is completed. This includes all standard 6-ft W6x8.5 posts at ½ or ¼ post spacing.

I also wanted to note that the drawing supplied shows the original upstream stiffness transition which utilized W6x12 posts. We have developed a simplified version incorporating only 6-ft long W6x8.5 posts that you may wish to consider.

https://mwrsf.unl.edu/researchhub/files/Report38/TRP-03-210-10.pdf

https://mwrsf.unl.edu/researchhub/files/Report32/TRP-03-243-11.pdf

https://mwrsf.unl.edu/researchhub/files/Report295/TRP-03-291-14.pdf

Thanks

Date February 21, 2019
Previous Views (177) Favorites (0)