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I wanted to get your opinion on the use of butterfly delineators (metal or plastic) that slip under the bolt on guardrail.
Below is a link to a website for our approved delineators along with the KDOT specification. KDOT uses a plastic type delineators as mentioned in the spec. We do state in our spec that these delineators need to be 350 approved. KDOT is placing these guardrail delineators on the maintenance side. However, I have attached our standard drawing that shows them to be riveted and these are being placed in the construction plans on the design side.
If you read down the email chain, FHWA checked with their office and said that there were no 350 approval letters. Also, they indicated that there is not a concern with the use of these delineators (assuming under a guardrail bolt). Anyway, I want to make sure that there is not a performance issue since we are saying it should be 350 compliant. Typically the maintenance personnel install these by sliding the plastic delineators under the guardrail bolt.
|Date||January 15, 2009|
The delineators should not be a concern for becoming a projectile and posing risk to oncoming traffic or to the occupants of the vehicle impacting the barrier. However, the delineators may imitate the behavior of the old steel washers and allow the rail to remain attached to the post and possibly become pulled down during impact events. The steel variety may seem to be a greater concern than those made with polycarbonate material. As an alternative, would KsDOT be willing to place the devices on the rail at non-post locations, on posts, or even glue/bond them to the rail?
|Date||January 15, 2009|
The location could be discussed internally again but I believe the easiest for maintenance folks (probably installing under guardrail bolt) will prevail if there are not any issues. We tried the glue years ago and it did not work. First snow, the delineators were knocked off. We found the rivet option worked.
I think there are many manufactures that describe placing these under the guardrail bolts like the link I sent you. The picture for the steel version from this manufacturer's site states "install quickly using existing guardrail bolts" by the detail showing the guardrail and delineator. (this is for the steel version) The attached email has further comments from the FHWA. I appreciate everyone weighing in on this and can you explain the effects of using a washer too in order to pass this along.
I have also attached a picture of the plastic version. Again, they indicate to install under guardrail bolts. No mention of performance or 350 compliance.
I called the supplier about specific details and they are checking into it. The only thing they could give me is listed on the product sheets below and I summarized this. Also, I asked this supplier for any testing or 350 compliance but I don't think they had a clue about what that meant (checking into it though). I did not see any mention of compliance on any website for these things.
AKT Plastic version (717):
- 5 ¼" x 3"
- approx. 0.085" thick
- High impact polycarbonate
AKT Steel version (567):
- 5 ¼" x 2 ¼"
- 12 guage galvanized steel
|Date||January 15, 2009|
Please note that the slot dimensions or washer plate size are not shown below. I have considered this issue more and still have concerns with the 12-gauge, steel galvanized component when used under the head of a guardrail bolt. As you are aware, the use of 3/16" rectangular guardrail plate washers have been highly discouraged with the use of strong-post guardrails. Although this component is thinner, 0.105 vs. 0.188", and has one end open, the potential remains for it to increase rail to block/post attachment. At rail splice locations, this device would add another rail thickness. At non-splice locations, it would simulate a two-ply splice. As such, I would not recommend the use of the steel device at rail splice locations. In addition, I am concerned about effectively adding plate washers, although thinner than prior designs, to the non-rail-splice locations. If crash testing demonstrates that the use of the steel components provide an acceptable safety performance, then use them as needed.
With regard to the thin polymer version, I believe that the head of the guardrail bolt would easily pull through the washer region.
|Date||February 5, 2009|
After review of the plastic and steel butterfly delineator designs, MwRSF, FHWA and KsDOT agreed that the plastic delineators posed little concern for adversely affecting guardrail performance due to their low thickness and material strength. However, there concern with the steel design acting like a washer could not be eliminated. Thus, the group recommended use of the plastic butterfly delineator designs until further research or testing verified the steel butterfly delineator performance.
|Date||March 24, 2009|
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