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Re: Shear Flow

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Inorder to apply the formula, you have to transform one of the material to 
the other. If you select steel as your material then transform the wood into 
steel by dividing the width of the beam by the modular ratio n (Es/Ew).  Then 
calculate your sectional properties of the transformed section.  

If you choose wood as your material then transform the steel into wood by 
multiplying the b or Q or I by modular ratio n.

Hope this will help.

Alfonso S. Quilala Jr., P.E.

In a message dated 2/14/00 11:48:23 AM Pacific Standard Time, 
ggobo(--nospam--at) writes:

<< 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

Gina T. Gobo, E.I.T.
 Structural Engineering
 DLR Group
 Ph. 206.461.6000
 Fax 206.461.6049