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RE: Low compressive strength - grout

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Jake,

Thanks for your thoughts.  I have my suspicions about why the strength
results are so low - it sounds as if the testing agency was notified of the
pour relatively late and that the batch may have been sitting on site for a
while (over an hour and a half) before casting cubes and prisms.  

We are planning to have the in-place wall tested.  UBC 2105.3.5 lists
provisions for testing constructed masonry (it references the UBC Standard I
mentioned).  I am betting that once we get those reults we'll find that the
in-place work is ok, but if not, I still wanted to ask the question so that
I could be armed with at least some kind of background knowledge.

The project is actually in Indiana.  If I look at an unreinforced wall per
empirical design requirements the wall would be just over the lateral
support height requirement.  But maybe close enough to add angles at top of
slab and bottom of beam at each floor to meet that requirement.  Hmmmm.

Peter



-----Original Message-----
From: Jake Watson [mailto:jwatson(--nospam--at)utahisp.com]
Sent: Sunday, June 30, 2002 5:30 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Low compressive strength - grout


Aside from the code aspects, two thoughts come to mind.  If the wall is a
shearwall, the grout becomes a major concern as it helps to tie rebar and
block together.  If it is not a shearwall, the grout is only a means to
transfer "shearflow" between the block and rebar for out-of-plane loads.  It
is very rare for the grout itself to actually be in compression for
out-of-plane loads.  The compression zone will likely be within the
faceshell of the block unit.  Of the items I've heard, the rebar lap appears
to be the most problematic.  But even that can be addressed if the stress in
the rebar is low.  If it is a non-load bearing backup wall, you may be able
to reduce the required lap based on stress in the steel.

If the project is in Connecticut, can you treat the wall as unreinforced
(and ungrouted)?

Does anyone know why the strength is so low?

Good luck,

Jake Watson, P.E.
Salt Lake City, UT

P.S. Have you considered in place testing of actual conditions?  It may be
cheaper to test a few wall samples rather than a more dramatic (and
expensive) solution.


-----Original Message-----
From: Peter Griem [mailto:griem(--nospam--at)slamcoll.com]
Sent: Friday, June 28, 2002 2:02 PM
To: 'SEAINT(--nospam--at)SEAINT.ORG'
Subject: Low compressive strength - grout


If the compressive strength of grout is low (say 1000 psi vs 2000
specified), but the grouted and ungrouted masonry prism strengths are
greater than 1.33 times the specified f'm - should there be cause for
concern?  If so, why?

Where can I quickly get a copy of UBC Standard 21-17?

Thanks in advance,

Peter Griem
The S/L/A/M Collaborative
80 Glastonbury Boulevard
Glastonbury, CT 06033

(860) 659-1010 x3389
griem(--nospam--at)slamcoll.com


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