# Transverse Shear

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```					   Transverse Shear
Built-up Beams and Shear Flow
Built Up Beams
Built up beams are made from two or
more pieces of material joined together
to form a single beam.
Such beams can be constructed in a
variety of shapes to meet structural
needs and provide a larger cross section
than ordinarily available. Figure 7-13
Box Beam
Other examples are a wood box beam,
constructed of two planks, which serve
as flanges, and two plywood webs.
Pieces are joined together with nails,
screws, or glue, in a manner that the
entire beam acts as a single unit.
Box beams are also made from steel,
plastic, and composites.
Glulam Beam
A Glulam beam is made of boards glued
together to form a much larger beam
than could be cut from a tree.
Glulam beams are used in the
construction of small buildings.
Plate Girder
This is commonly used
in bridges and large
buildings.
The girders consist of
three steel plates joined
by welding.
much larger sizes than
available with wide-
flange or I-beams.
Built Up Beams
Built up beams must be designed so that the
beam behaves as a single member
The design calculations involve two phases
Beam design as though made of one piece,
looking at both bending and shear stresses
Connections between the parts (nails, bolts,
welds, or glue) are designed to make sure the
beam behaves as a single entity
Built Up Beams
Connections must
be strong enough to
transmit the
horizontal shear
forces acting
F3
between the parts of
the beam
To find these forces
we use Shear Flow.
Recall: F  dM ydA
3
I 
Shear Flow
Shear Flow q is the horizontal shear
force per unit distance along the
longitudinal axis of the beam.
Since the force acts along the distance
dx, the shear force per unit distance is
equal to:
F3 dM  1 
q         ydA
dx dx  I 
Shear Flow
Replacing dM/dx by the shear force V,
and noting the first moment of area Q,
we get the Shear Flow Formula.

VQ
q
I

```
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