huangyhg

check of cantilever beams
hi everybody:
i have planted column at the edge of cantilever beam the length of that cantilever is 0.5 meter.
the dimension of beam is 0.8 m width 0.33 height (hidden beam) but the column load is small.
i check the rft of beam and stirrups, and i check the deflection all is ok as per aci 318-2005 and ibc-2003.
but i am still afraid because the depth of beam is very small and the planted columns at the edge.
the arch engineer refuse to increase the depth of beam with out big reason because that is will effect on building facade.
are my checks enough or i needing more check?
many thanks.
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did you check bar development? for a short cantilever like this, you need to use smaller bars.
daveatkins
why are you afraid? do you think the load from the column will be higher than you expect?
from what you described the beam has no lateral restraint, did you check this?
also the beam is very short if the load from the column is small like you said then it should be a problem.
swelm,
believe it or not, in amny codes this would be considered a 'deep beam' due to its span/depth being less than 1.5. the term is relative to the span rather than the actual depth of the beam.
that said, the beam would act more like a strut and tie model than a bending and shear one so i would check it as that also.
see
thank you for all answer
but do u think i need to check for punching ,becuase the depth of beam is very small 330 mm or not
good point about the deep beam theory
punching shear would be taken up by the stirrups just need to check if they can take the shear.
i've never heard of checking punching shear for a beam.
you should always consider punching shear, but in most cases with beams, it just amounts to knowing by experience that punching does not control. with wide, flat beams, it may, but in an 800 wide, 330 deep beam as in the op, beam shear will control. as csd72 pointed out, in this case of a short cantilever, if you get the strut/tie action working, there is no problem.
i am wondering how punching shear could ever control shear design in a beam. the only case i can imagine for punching shear would be a point load with no other loadings (which obviously can't happen in rc due to the self weight).
for the case of a single point load on a beam, the sum of the shears on both sides of the point load will equal the point load. if you design for that shear as regular beam shear, then the sum of the shear resistances on both sides of the beam will have to be equal to (or greater than) the required punching shear.
i can not envision any situation in which punching shear could possibly control for a beam.
am i missing something?
i guess it depends on how you define a "beam". in the case of a wide, flat beam, the punching shear perimeter can be substantially less than the beam shear effective width.

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