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Plant Mix Curb Under MGS Guardrail

Question
State	WY
Description Text	We have been using about a 3 1/2 to 4 inch plant mix curb under MGS on some mountain roads were erosion of the slope is critical. I know MGS has been tested to 350 with a 6 inch curb up to 6 inches in front of it. But then I remembered you had some concern about small vehicle uplift during a transition test with a 4 inch curb and again with the MGS with one post missing and a curb. I remember you fixed both with double nesting the rail. For a standard post spacing, do you think we are o.k. with the curb configuration shown herein?

Question

State

Description Text

We have been using about a 3 1/2 to 4 inch plant mix curb under MGS on some mountain roads were erosion of the slope is critical. I know MGS has been tested to 350 with a 6 inch curb up to 6 inches in front of it. But then I remembered you had some concern about small vehicle uplift during a transition test with a 4 inch curb and again with the MGS with one post missing and a curb. I remember you fixed both with double nesting the rail. For a standard post spacing, do you think we are o.k. with the curb configuration shown herein?

System Performance Evaluation

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Road Closure Gates
Thrie Beam Guardrails

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Date June 7, 2018
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Attachment WY Curb.jpg

Response
Response (active)	You are correct that the MGS has been tested to MASH TL-3 with a 6” AASHTO Type B curb installed 6” in front of the face of the guardrail. As you noted, in the small car testing of the this curb and the MGS with an omitted post, we had rail rupture due to wedging of the vehicle between the rail and the curb and the resulting combined loading of the rail splice. We also saw a rupture of the MGS upstream stiffness transition to thrie beam AGT when the vehicle was wedged between a 4” wedge curb and the asymmetric W-thrie transition section. In both cases, nesting the rail alleviated that issue. We also successfully tested the MGS to MASH TL-3 with a 6” AASHTO Type B curb installed 6” in front of the face of the guardrail using the standard post spacing with both the 1100C and 2270P vehicles. In the 1100C test, we did observe some rail tearing at a splice, but the rail maintained its integrity. For the installation shown below, the shorter wedge shape curb and reduced offset should improve performance based on previous curb testing. In addition, it should reduce the amount of vehicle wedging between the rail and the curb. Thus, I would believe that the MGS at 6/-3” post spacing would work fine with this curb configuration. Thanks

Response

Response
(active)

You are correct that the MGS has been tested to MASH TL-3 with a 6” AASHTO Type B curb installed 6” in front of the face of the guardrail.

As you noted, in the small car testing of the this curb and the MGS with an omitted post, we had rail rupture due to wedging of the vehicle between the rail and the curb and the resulting combined loading of the rail splice. We also saw a rupture of the MGS upstream stiffness transition to thrie beam AGT when the vehicle was wedged between a 4” wedge curb and the asymmetric W-thrie transition section. In both cases, nesting the rail alleviated that issue.

We also successfully tested the MGS to MASH TL-3 with a 6” AASHTO Type B curb installed 6” in front of the face of the guardrail using the standard post spacing with both the 1100C and 2270P vehicles. In the 1100C test, we did observe some rail tearing at a splice, but the rail maintained its integrity.

For the installation shown below, the shorter wedge shape curb and reduced offset should improve performance based on previous curb testing. In addition, it should reduce the amount of vehicle wedging between the rail and the curb. Thus, I would believe that the MGS at 6/-3” post spacing would work fine with this curb configuration.

Thanks

Date June 7, 2018
Previous Views (319) Favorites (0)