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We have been looking into a new single slope barrier, AGT design
One alternative design has recently been proposed. It uses an 8-inch high curb with a front face
Attached is a draft drawing showing this design
Let me know if you need any further information.
|Date||April 14, 2016|
Previous full-scale testing has shown that the addition of a curb has generally reduced the amount of snag on the rigid buttress. That being said, the face of the buttress has typically been tapered back in conjunction with the curb. I don't believe any AGT has been successfully tested without a taper of the rigid buttress (of the toe or the entire front face). Thus, snagging may still be an issue. The smallest taper that i could find that was successfully tested on a SS buttress was 4" laterally, by 22" longitudinally - reference TRP-03-47-95. That AGT configuration did not utilize a curb, so there is a chance that adding a curb could help reduce snag, but it has not been tested/evaluated.
My biggest concern with the proposed idea is a potential for vehicle instability with an 8" tall curb. All of the previously crash tested (350 and MASH) AGT designs utilized 4 inch tall curbs. Testing of W-beam guardrail with a curb has used curb heights up to 6". There is no data available on vehicle interactions with an 8" tall curb. As such, my concerns are that excessive climbing and rolling may occur during vehicle impacts. Again, there is no data proving that this is a problem, but there is also no data demonstrating the crashworthiness of an 8" curb. However, I would feel better about leaving the curb height at 4 inches throughout its length - the curb height typical of AGT's that has been shown to be crashworthy.
If you do decide to utilize a taller curb, you are correct in transitioning it down to a 4" tall curb prior to the curb extending below the W-to-thrie beam transition element. Previous testing has demonstrated the sensitivity of this region of the AGT, and we would not want to induce further vertical climb and increased vertical rail loads.
|Date||April 25, 2016|
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