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Shear Flow

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I have question about composite beams:

I have a wood glulam beam that I would like to reinforce by adding a steel
channel to both sides. I am trying to find the shear flow at the channel to
wd beam contact area so that I may figure our how many bolts I need to
faster the composite beam together. I am using the formula f = QV/I, where V
is the maximum shear load on the beam, I is the moment of inertia for the
composite section, and Q the first moment of inertia of the glulam beam that
is in contact with the channel = yA where, y is the distance from the
centroid of the block of wd in contact with the channels to the neutral axis
and A is the area of the same block of wd. If I am using a channel that is a
C12X20.7 and a 6.75X31.5 glulam, Q = ((12/2)-dist to neutral axis of entire
section)*6.75*12=248in3. I = 17964.83 in4 and V = 48kips. f = 8kip/ft which
seems very high. 

The shear flow that I get seems very high. Do I have to use the transformed
section in order to get the shear flow? (i.e. transform the wd beam into an
equivalent steel member in order to get the correct shear flow). Or, is
using I of the composite section based on the geometry of the cross section
ok?


Gina T. Gobo, E.I.T.
Structural Engineering
DLR Group
Seattle
Ph. 206.461.6000
Fax 206.461.6049
ggobo(--nospam--at)dlrgroup.com