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RE: Rigid Diaphragm

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Dear Jim:

It is very common nowadays in Chile and in Peru, my country, to use 4 inch
thick concrete slabs in apartment buildings, with spans that are smaller
than 12 feet. We have done some Finite Element Analysis of them and have
found they have some deformation for seismic loads, dynamic and static, but
not as much to consider them rigid diaphragms.
The problem is more how to make a good connection between the new walls and
the existing slab to guarantee that analysis considerations will be as the
repaired building.
About having the seismic loads equally distributed to the shear walls,
depends on the location of the new walls, that means, simetrically, but even
in that situation, you would have to consider accidental torsion.
If the slab has some cracking, you could use epoxy injection. We have
performed some investigation on real size specimens which were tested for
lateral load and then after the damage, we repaired them with epoxy
injections, tested again and obtained the same results as the new structure.


Walter Sheen
----- Original Message -----
From: frp2000 <frp2000(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Friday, March 09, 2001 5:30 PM
Subject: Rigid Diaphragm

> I have a situation where an existing slab is 4" thick. Owners would like
> make it "more" rigid", to distribute seismic loads to new shear walls
> equally.
> Is this possible?? If so, how??
> jim k