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F-shape Barrier Strap Tie-Down Bolt Size

Question
State KS
Description Text

I am trying to finalize our standard details for the strap anchor option on the F3 barrier system.  While working on the details for the RED HEAD Multi-SET II anchor I noticed a discrepancy in the bolt length.  All of the details I have received to date show a 2.25" Grade 5 bolt through the strap and into the anchor.  However, when I look at the anchor specifications, the threading inside of the anchor is only 1.25 inches deep.  So, if the anchor is embedded the 3 3/16", which is also the length of the anchor, and it is threaded for 1.25" with 1/2" of plate steel for the strap, the bolt could not be any longer than 1.75", unless the anchor is embedded at least 3 11/16" (the top of the anchor is ½" below the top of the pavement).

 

Can you shed some light on this issue, or some additional details on how the anchor was installed for the test?

Keywords
  • Temporary Barriers
Other Keywords none
Date July 6, 2006


Response
Response

KsDOT has brought an issue to our attention regarding the bolt length used in the F-shape PCB Strap Tie-Down design. This design uses the RedHead Multi-Set II Drop-In anchor to anchor the steel retainer straps to the concrete bridge deck. We used a ¾" dia. drop-in during our testing that had an embedment of 3 3/16" and a threaded depth of 1 ¼". When we tested the system, MwRSF used a 2 ¼" long x ¾" dia. Grade 5 hex bolt. The system test was successful, and we specified that bolt size for our final plans. When looking at the anchor geometry, KsDOT noticed that we had ½" more length on our bolt than the threaded length of the anchor and wondered if that was an issue. MwRSF contacted engineers at RedHead about this question. The response from RedHead was that they did not advise using bolts that threaded farther into the anchor than the 1 ¼" thread depth. Their concern was that using bolts with longer lengths could cause excess expansion of the base of the anchor and potential fracture of the tabs at the base of the anchor. This would cause a possible reduction in anchor capacity.

 

Based on this new information, we are recommending that the states revise their details for this system to reflect the use of 1 ¾" long x ¾" dia. Grade 5 hex bolts with the drop-in anchors to eliminate any potential problems with the anchors.

Date July 10, 2006


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