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Headwall extensions (curb) under side-mounted, weak-post MGS on culverts

Question
State	IN
Description Text	Indiana often paves a shoulder adjacent to a culvert headwall. The shoulder pavement paved within 2 inches or less (vertically) to the top of headwall. We have some districts that would like to have a little bit of a lip to catch some water. Similar to the headwall project for the long span, would a 2” projection be acceptable for the headwall in combination with side mounted, weak post guardrail as well? Thank you

Question

State

Description Text

Indiana often paves a shoulder adjacent to a culvert headwall. The shoulder pavement paved within 2 inches or less
(vertically) to the top of headwall. We have some districts that would like to have a little bit of a lip to catch some
water. Similar to the headwall project for the long span, would a 2” projection be acceptable for the headwall in
combination with side mounted, weak post guardrail as well? Thank you

System Performance Evaluation

System Types
Road Closure Gates
Thrie Beam Guardrails

Applications

System Features

Date May 14, 2019
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Response
Response (active)	From the recommendations chapter of the long-span MGS report, we had written that headwalls extending above ground line would represent vertical curbs underneath the guardrail and could pose a vehicle stability hazard. As such, we recommended that the headwall extend no more than 2 in. above the roadway surface. More recent testing has shown that curbs under guardrail can lead to tearing and/or rupture of the rail during small car impacts (MGS with curb, MGS with curb and omitted post, and upstream stiffness transition with curb testing). This would be further support for limiting the height of a “curb” under the guardrail. I believe that the same 2 in. maximum would be applicable for the side-mounted, weak-post MGS on culverts as well.

Response

Response
(active)

From the recommendations chapter of the long-span MGS report, we had written that headwalls extending above ground line would represent vertical curbs underneath the guardrail and could pose a vehicle stability hazard. As such, we recommended that the headwall extend no more than 2 in. above the roadway surface. More recent testing has shown that curbs under guardrail can lead to tearing and/or rupture of the rail during small car impacts (MGS with curb, MGS with curb and omitted post, and upstream stiffness transition with curb testing). This would be further support for limiting the height of a “curb” under the guardrail. I believe that the same 2 in. maximum would be applicable for the side-mounted, weak-post MGS on culverts as well.

Date May 15, 2019
Previous Views (194) Favorites (0)