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Using 12-Inch Block on TTI's Downslope Beam Guard Installation

Question
State WI
Description Text

We are looking at using a modified version of the beam guard tested by TTI.  Specifically we would like to use a 12-Inch block instead of the 8-Inch block tested in Abu-Odeh A, Ha K, Liu I, Menges WL. MASH TL-3 Testing and Evaluation of the W-Beam Guardrail on Slope. TTI; 2013. Report No.: 405160-20.

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Other Keywords none
Date September 21, 2020
Response
Response

We believe you can use a 12” deep blockout with that system, but you will need to maintain the 12” offset from the front face of the post to the slope break point. This would place the face of rail approximately 4” in front of the slope break point.

 

We do not recommend using a 12” deep blockout and pushing the post 4” farther down the 2H:1V slope. This would increase the cantilever distance on the post and reduce post embedment. These two factors would act to reduce the overall lateral stiffness of the system and may degrade the barrier performance.

 

We have noted in the past that you can use the MGS with 8’ or 9’ posts at the slope break point without blockouts as an alternative. We have also noted that the 6’ post version of the MGS can be installed at the slope break point without blockouts, but that system requires better control of the soil behavior for your installations and has higher working widths.

 

Date September 23, 2020