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Re: Shear Flow

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"For a beam made of two or more materials with different moduli of
elasticity, show that  Equation T=VQ/It remains valid provided that both Q
and I are computed using the transformed section of the beam and provided
that t is the actual width of the beam at the point where T is computed."

>From Beer and Johnton's Mechanics of Materials, Second Edition, McGraw-Hill,
Inc. 1992, page 305

Chris Towne, E.I.T.
Chapman Technical Group

----- Original Message -----
From: "Gobo, Gina" <ggobo(--nospam--at)>
To: "'seaint'" <seaint(--nospam--at)>
Sent: Monday, February 14, 2000 2:42 PM
Subject: Shear Flow

> 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
> 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
> 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
> 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
> and A is the area of the same block of wd. If I am using a channel that is
> C12X20.7 and a 6.75X31.5 glulam, Q = ((12/2)-dist to neutral axis of
> section)*6.75*12=248in3. I = 17964.83 in4 and V = 48kips. f = 8kip/ft
> seems very high.
> The shear flow that I get seems very high. Do I have to use the
> section in order to get the shear flow? (i.e. transform the wd beam into
> 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
> ok?
> Gina T. Gobo, E.I.T.
> Structural Engineering
> DLR Group
> Seattle
> Ph. 206.461.6000
> Fax 206.461.6049
> ggobo(--nospam--at)