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Concrete T beams/ ribbed slabs

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 I am doing an analysis on an existing building and I have one last check
that is giving me fits, and the ACI is a little unclear. What I am trying to
do is check the bending and shear stress in the flange of a T beam, that is,
the stress transverse to the web. There is a point load at the very end of
the flange, and the joint where two T beams meet, and this cantilevered
moment causes a bending stress at the face of the web where the flange joins
the web. I hope this is clear.

ACI 8.10.5
Where primary flexural reinforcment in a slab is considered as a T-beam
flange is parallalel to the beam, reinforcment perpendicular to the beam
shall be provided in the top of the slab in accordance with the following:

     8.10.5.1   - Transverse reinforcement shall be designed to carry the
factored load on the overhanging slab width assumed to act as a cantilever.
For isolated beams, the full width of overhanging flange shall be
considered. For other T-beams, only the effective overhanging slab width
need be considered.


I do not know what they mean by the full width or the effective width of the
overhanging slab. The way I assumed you were supposed to check it was from
the edge of the slab to the face of the web where the flange cantilevers
from. A bigger question for me is how wide of  a strip to use as a model for
the beam width of the flange. Since the transverse reinforcement is at 8"
o.c., and this seems like a reasonable width, this is what I used. The
flange fails, it is only 50% of the required factored moment.

Another question is do you know anything specific I should be aware of in
concrete construction from the 1930s? I was assuming 3000psi concrete and
fy=60000psi, but I am thinking at least the steel is probably less. It does
not say on the drawings I have. The transverse reinforcement is called out
as 1/4" diameter bars.

The specifics if you want to know:

T-beam
web width= 5"
depth total= 10"
flange thickness= 2"
flange width=10" from face of web, or 25" total (10" x 2 flanges + 5" web)

Transverse/temperature reinforcement: 1/4" diameter bars @ 8" o.c. (in a 2"
flange/deck)


Thank you in advance for any suggestions/ advice.

Andrew Kester, EI
Longwood, FL




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