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Re: Using steel chains as concrete reinforcement??

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Checking my edition of "Handbook for Mechanical Engineers" by Baumeister and Marks, which provides a guide for high-test steel chain:  a working load limit for 3/4" chain is 16.2 kis, with a minimunm proof test of 27 kips and minimum break-test of 25.2 kips. 

According to the description " this type of chain provides good reliability and is widely used for load binding, tie-downs, and similar applications where failures would be costly......."

Neil Moore, SE, SECB
shingle springs, california


At 10:23 AM 4/30/2007, Michael Hemstad wrote:
Ibrahim Mohamed wrote:
"I'm working on a job in which the engineer is using a novel way to
reinforce CMU walls. He's using steel chains instead of rebar, inserted
from the top and then full grouted with 4000psi concrete. I guess he's
been asked to justify the process and so he's come to us to do an
evaluation. I was wondering if anyone had come across such a situation
before and could advice us about the viability of such a process.
Just from first glance, I feel that using chains as concrete
reinforcement would lead to local stress concentrations that could cause
the chain to break or yield locally. Perhaps it might be ok to use these
chains at a lower strength value than what they're rated for.
Any advice would be greatly appreciated.
Thanks
ibrahim"
 
Ibrahim,
as others have noted, I'd be concerned about knowing that the chain was in the right place, i.e. in the center of the cell.  I'm concerned enough about that with rebar, and they hold their position a lot better than chain.  To that end, I'd want the chain held down, and a nominal tension applied to keep them more or less straight.
 
As Mark Gilligan mentioned, the Young's Modulus of chain won't be anywhere near 29,000 ksi.  I'm remembering the E for bridge strand being somewhere around 14,000 or 16,000 ksi, because it untwists; chain has to be a lot less than that as the links deform.  Even considering Gregory from Oz's point that the links will be filled with concrete, you might be dealing with 10,000 ksi or less as a guess.  So, for a given area or even a given strength, the chain won't be as effective as rebar unless it has significant prestress.
 
I chuckled at this idea initially, until I started to think about the retrofit-under-a-low-ceiling problem.  Still, couldn't the floor above be drilled and a rebar dropped into the cores?  If not, I'd want a lot of chain with as much prestress as I could get if it was my signature on the drawings.  Most of the cost for a retrofit project like this is in mobilization and chopping in to the cells.  Make the chain big.
 
My two cents' worth.
 
Mike Hemstad, P.E., S.E.
MBJ
Minneapolis, Minnesota

 
Michael Hemstad, P.E.
 
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Meyer, Borgman and Johnson, Inc.
 
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