corbel or cantilevered beam

huangyhg

corbel or cantilevered beam
folks,
this may seem to be a stupid question, but can anyone offer an explanation:
i have a stub column which is to be designed to carry a horizontal reaction. it has no axial load on it, meaning it is a cantilevered beam. the stub is 3'-0" high and 4'-0" wide and 2'6" deep.
my options are to design it as a cantilever beam and provide shear reinforcing parallel to the direction of force or to design it as a corbel and provide closed hoops perpendicular to the direction of shear. it may be cast at a different time, with rebar already doweled in during the first pour.
how do i decide which method to design it by?
cantilever beam.  how big is the load?
this is similar to the difference between a wall design or a column design... it's mostly engineering judgement, but should be based on what the behaviour should be like.
given your shape described, this is certainly not shaped like a beam, it is a corbel.
i would use strut and tie.
cheers,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
shear vu  = 480 kips, ultimate.
moment arm of 18"
      /    /|
     /    / |  
    /____/  /   <--- direction of force
    |    | /
    |    |/
    -------------
ok.  that's a big load.  
strut and tie.
don't know which code you are using. for aci, you will have to meet certain geometric limits to call it a corbel. for your case, just design it as a cantilever beam.  
i have a very small shear span-to-depth ratio. of the order of 0.67 < 1.0.
the shear stress you'd get by designing it as a cantilever beam would be monstrous, right?  something on the order of like 500 psi or something like that?
think this is an odd case of deep beam. you will require facial reinforcing in both directions to prevent crack from happening.
if designed as a cantilever beam, i would need 8 legs of #4 bars (av = 1.6 in2) spaced at 6" o.c. and a flexural reinforcement of 7 in2. fc' = 4000 psi.