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RE: Tin Pan Joists

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Aside from being "built that way", I have heard of such deflections
occurring as a result of decades worth of creep and poor concrete mixes in
very old concrete buildings.  A friend once told me that an old building was
demolished at the University of Texas partly due to this effect, perhaps
someone on the list knows about that?  It was a second hand story, so I am
not completely sure of the accuracy.  If you can calculate or estimate a
reasonable Ie (check ACI 318-99 9.5.2.3), you can get an idea of how
reasonable the deflection is, keeping in mind that long term deflections may
be 2 or 3 times the DL loading value that you calculate once you include
creep (see 9.5.2.5).  While these equations may look a little inaccurate, I
actually used them to correctly predict a long span precast beam deflection
once, so they are somewhat reasonable as far as approximations go.  Also,
keep in mind that the steel used is probably not the kind we use today.
Values of fy of 33ksi or 40ksi (with fu from 55ksi to 85ksi) were common.
The PCA published an article about this by Gustav Erlemann a few years back;
it is intersting, albeit fairly general.  Good luck.  

Paul Crocker

-----Original Message-----
From: David Handy [mailto:dhandy(--nospam--at)trg.ca]
Sent: Monday, January 08, 2001 2:18 PM
To: seaint(--nospam--at)seaint.org
Subject: Tin Pan Joists


I have looked at a building with stay in place tin pan floor joists that 
was building approx. 1930. I have the original drawings however the 
drawings state only 12" T.P.J. + 2" slab. No reinforcement for joists is 
given. I was called in to look at it because there is a 1" deflection in 
the floor over a span of 24' without any significant live loading. The 
condition of the floor slab is terrible and they want to level and smooth 
it with DuraCap a gypcrete product.
They removed a 1" thick layer of what looked like solid asphalt or tar. 
This stuff weighed about 13 psf. Never seen that before. Went up in flames 
after 5 seconds. Does anybody know what this stuff is? There was linoleum 
over it.

As far as the structure goes I am at a bit of a loss as too how to check 
this floor and to why there is such a large built in deflection without any 
significant live loads...Apart from the old standby...it was built that way.
I am planning to remove at bit of the pan at the quarter point and chip the 
concrete off to see what the bottom bars are. I will also inspect the 
concrete between the forms at the bottom of the ribs to check for any 
cracks. I can also do some inpact tests on the slab to check for concrete 
strengths although I don't know how accurate these will be on a 2" thick
slab.
Any thoughts or related experiences.

David Handy, P.Eng.
dhandy(--nospam--at)trg.ca