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Removable Guardrail Post

Question
State	MO
Description Text	The Missouri boot heel (extreme southeast) consists entirely of flat farmland drained by a network of levees and ditches. In places, these ditches run parallel to one another, separated by as little as 50 ft. In one location on US 412, there are five parallel ditches in close proximity (See Aerial photo below). Shielding the bridge ends and the ditches are critical, but so is maintenance access to the levees. In that vein, previous designers have placed wood posts in sleeves so that a single post and rail section can be periodically removed for access (See Opening photo below). I am unaware of any crash testing for this arrangement, but Missouri has had good experience with it for a couple of decades. The Westbound lanes of 412 are about to receive guardrail upgrades and the levee district has requested that the DOT use the single socketed post again, only with a steel post to avoid the swelling that occurs with wood. Here are the questions: 1. Has a socketed guardrail post (wood or steel) ever been tested? 2. If not, is the driven socket a reasonable variance of a driven post? 3. Is there any proprietary product that will afford the needed access?

Question

State

Description Text

The Missouri boot heel (extreme southeast) consists entirely of flat farmland drained by a network of levees and ditches. In places, these ditches run parallel to one another, separated by as little as 50 ft. In one location on US 412, there are five parallel ditches in close proximity (See Aerial photo below).

Shielding the bridge ends and the ditches are critical, but so is maintenance access to the levees. In that vein, previous designers have placed wood posts in sleeves so that a single post and rail section can be periodically removed for access (See Opening photo below). I am unaware of any crash testing for this arrangement, but Missouri has had good experience with it for a couple of decades.

The Westbound lanes of 412 are about to receive guardrail upgrades and the levee district has requested that the DOT use the single socketed post again, only with a steel post to avoid the swelling that occurs with wood.

Here are the questions:
1. Has a socketed guardrail post (wood or steel) ever been tested?
2. If not, is the driven socket a reasonable variance of a driven post?
3. Is there any proprietary product that will afford the needed access?

System Performance Evaluation

System Types
Approach Guardrail Transitions (AGTs)
Bridge Rails
Road Closure Gates
Thrie Beam Guardrails

Applications

System Features

Date February 25, 2014
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Attachment 412 Aerial.jpg Attachment 412 Opening.jpg

Response
Response (active)	Strong-post guardrail systems installed into rigid sockets (or rigid pavements) have shown negative results through full-scale crash testing. The restriction on rotation led to increased forces, rail tearing, and vehicle penetrations. Thus, strong-post systems are not recommended for use within a rigid socket system. On the other hand, if the socket was simply a steel tube/sleeve for the post to sit in, it would translate within the soil similar to the post itself. Similar flange widths and embedment depths between the steel socket and the original post will result in similar soil resistances and similar barrier performance. However, it is recognized that the socket will have to be slightly larger than the post itself, and will subsequently create higher soil resistances. Thus, it is important to size the socket such that the post fits snugly within the socket and the socket width is a close as possible to the width of the post. Further, it is recommended to utilize steel posts over wood posts for these socketed installations. Within a socket, the post will be subjected to hard points and stress concentrations at the top of the socket. This may lead to premature fracture of a wooden post and degradation of the barrier’s safety performance. The same hard points and stress concentrations will only cause a steel post to yield and bent over – maintaining lateral resistance while doing so. Thus, switch to steel posts has more benefits than simply eliminating the wood post swelling issue.

Response

Response
(active)

Strong-post guardrail systems installed into rigid sockets (or rigid pavements) have shown negative results through full-scale crash testing. The restriction on rotation led to increased forces, rail tearing, and vehicle penetrations. Thus, strong-post systems are not recommended for use within a rigid socket system.

On the other hand, if the socket was simply a steel tube/sleeve for the post to sit in, it would translate within the soil similar to the post itself. Similar flange widths and embedment depths between the steel socket and the original post will result in similar soil resistances and similar barrier performance. However, it is recognized that the socket will have to be slightly larger than the post itself, and will subsequently create higher soil resistances. Thus, it is important to size the socket such that the post fits snugly within the socket and the socket width is a close as possible to the width of the post.

Further, it is recommended to utilize steel posts over wood posts for these socketed installations. Within a socket, the post will be subjected to hard points and stress concentrations at the top of the socket. This may lead to premature fracture of a wooden post and degradation of the barrier’s safety performance. The same hard points and stress concentrations will only cause a steel post to yield and bent over – maintaining lateral resistance while doing so. Thus, switch to steel posts has more benefits than simply eliminating the wood post swelling issue.

Date February 28, 2014
Previous Views (80) Favorites (0)