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Re: Structural importance of full-depth shrinkage cracks

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Rajendran, I don't understand the reasoning behind your comments at all.

1.  Whether the cracks would close before full catenary tension could develop would depend on the geometry--crack width, span, rigidity of the surrounding structure, etc.  I don't think we can make a blanket statement such as yours without knowing the details of the situation.

2.  Yes, catenary tension "could" be large, depending again on the geometry, loads, etc. 

3.  I don't know how age and being intact suggest that it is only experiencing flexure. 

4.  "okay as it is"??  I don't know if it's loaded or unloaded, whether it's barely surviving under dead load alone and on the edge of collapse, or whether it has considerable remaining live load capacity.  Do we have adequate information to know these things?  Is the slab sagging significantly?

5.  Lacking evidence to the contrary I suggest that any deflection should be eliminated by shoring and that the cracks should be filled with a non-shrinking grout at least as strong as the existing concrete, as you suggest.

Ralph

In a message dated 2/27/05 6:34:24 AM, rakamaka(--nospam--at)yahoo.com writes:

But, before the full catenary tension could develop,
the crack would have closed by compression at top
fibres of the section, in which case the load would be
resisted by flexure. Also, remember that a catenary
behavior would generate large horizontal forces at the
supports. The fact that one of the quoted structure is
20 years old and the fact that it is still in tact
suggests that it is experiencing only flexure.
Theoretically, the structure is okay as is. However,
my preference would be to seal the crack all the way
with a liquid consistency epoxy grout. Sika or
Masterbuilders or Five Star should be able to
recommend a suitable product.

Rajendran

--- Rhkratzse(--nospam--at)aol.com wrote:

> In a message dated 2/26/05 11:46:45 PM,
> smaxwell(--nospam--at)engin.umich.edu writes:
>
> > there needs
> > to be some flexural compression to "balance" out
> the flexural tension.
> >
> Yes, but there may be a significant amount of pure
> catenary tension in the
> bottom rebar that doesn't need to be balanced by any
> compression at the top.  
> Frankly I can't imagine how there could be an open
> crack at the top, or full
> depth, without a whole LOT of catenary tension in
> the rebar.
>
> Ralph Hueston Kratz, S.E.


Rhkratzse(--nospam--at)aol.com

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