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Movement of cable anchors

Question
State OH
Description Text

We need your opinion on an issue
we are noticing with some of our Nucor Cable End anchors.  Some
background:



Nucor now has 2 types of cable
guardrail end anchors (see attached PDFs).  The TTI version which we
like.  And the Barrier Systems version, which we’ve had issues with.



Typically these systems were
installed in the summertime, and we first notice the issue the following
spring. It seems when the ground thaws and gets softer, and the snow has
melted, but it is still cold enough to have higher tension values, we were
getting some movement in the anchors.  The contractor who does 90% of our
cable installations in Ohio says he doesn’t skimp on the foundations, but adds
a little more concrete than even the shop drawing calls for just to be more conservative. 
Based on some of the photos I’m not entirely convinced that was actually
happening in the field…



The attached .jpgs show varying
amounts of gaps between the soil and the foundations of the anchors.  We
are debating the replacement of these anchors that have signs of shifting or
movement.  Certainly these systems have been getting impacted over the
past year(s) and have been performing satisfactorily.  We just don’t
really know how critical of an issue we have.  The bottoms of the anchor
foundations should still be below the freeze/thaw depth.  We plan to keep
an eye on them to see if they are creeping any more over time, or if it was
just a one springtime thing.



How much movement or shifting do
you think we can allow on these anchors before needing to replace them?  I
know Indiana has had some issues with this anchor in the past completely
pulling out.  We had a couple of poor installations that did, too, upon
the initial tensioning.  But since this occurred while the contractor was
still on site, we were able to have it resolved immediately.  Now we just
aren’t sure what to do for the one that seemed to have creeped a little bit
over time.



 



Thanks for any advice.



Keywords
  • Guardrail
Other Keywords Cable anchors
Date August 12, 2013
Attachment Nucor_Ancor-BarrierSystems_end.pdf
Attachment Nucor_Ancor-TTI_end.pdf
Attachment MovingAnchor1.JPG
Attachment MovingAnchor2.JPG
Attachment MovingAnchor3.JPG
Attachment MovingAnchor4.JPG
Attachment Nucor-TTI_Ancor.jpg


Response
Response

From a brief review of the photographs and design details, several points are worth noting.

 

First, the diameter of the concrete shafts are approximately equal, but the TTI shaft is embedded around 20 in. more used in the New Zealand system.

 

Second, the TTI system has an individual anchor for each cable, while the NZ system has all cables directed into the anchor system.

 

Third, the NZ upward shaft movement appears to be a function of the relative distance away from the third shaft location. The third shaft location appears to be a rotation point around which shafts 2 and 1 are incrementally jacked upward and out of the hole. This upward movement or easier shaft movement may be occurring during high loading events, re-tensioning of cables after impact events, creep after consolidation of soil on inward side of anchor holes over time or during impact events which may increase gaps around concrete shaft, or combinations thereof. The load path in the NZ system may seem more conducive for lifting end concrete shaft out of the holes.

 

Deeper concrete shafts would likely eliminate this phenomenon in the NZ system. I would suggest raising this concern with Nucor so that they are aware of this situation and can fix it in future installations, or even existing systems where soil and environmental conditions make it easier to occur.

 

Our preliminary thoughts would be that replacement may be appropriate if the end shaft has raised nearly 2 in. or so. However, it may be beneficial to also pose this question to the manufacturer to get their thoughts on the potential for degraded barrier performance when shafts 1 and 2 are already jacked above grade.

 

Date August 12, 2013


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