the
tributary area dynamic. Additional bracing in the form of blocks or
cross bracing is used |
to keep
the joists from buckling or twisting under load. Joists are
typically solid wood |
planks.
They may also be composite structures such as truss joists, and
Ι-shaped
beams |
comprised of wooden top and bottom chords glued to a narrow strip of wood
paneling. |
. |
 |
Fig. 210 - Joist bracing |
|
|
◄ a) block bracing |
b) cross bracing ► |
(demonstration models) |
click image to enlarge |
|
. |
The wood
framed walls of the structure are then erected on top of this platform.
They are |
usually
comprised of many evenly spaced vertical 2 x 4 inch wooden studs. Wooden
panels, |
called
shear panels, are nailed to the outside face of the stud wall framing
to brace the wall |
against
lateral loads and to keep the studs from buckling under load.
Compressive forces |
are induced by the load of the above ground structures such as the roof
rafters or floor joists |
that rest on the top plate of the load bearing walls. The
walls transfer these compressive |
forces to the foundation. Shear forces are induced
in the walls by loads applied parallel to |
their
plane such as wind and seismic shaking. |
. |
For
example, strong winds try to overturn the wall which is fastened to the
foundation. This |
causes
the top plate of the wall to try to shear past the bottom plate just as we
saw before |
for
beams and trusses. Diagonal bracing is used between the studs in
addition to the shear |
. |
 |
Fig. 211 - Shearing of a |
 |
wood framed wall |
◄ a) shearing action |
b) bracing and panels |
prevent shearing ► |
(demonstration models) |
|
. |
panels,
which resist the shear forces by means of plate action. That is, the
entire wall acts |
as one
integral plate. And all the walls are joined together edge to edge
at their commonly |
shared
edges to make a plate-like box structure. Where openings are cut
into the stud wall |
framing
for windows or doors, wide wooden header boards are used to span the top
of the |
opening
so as to carry the downward compressive load of the missing stud columns.
The |
ends of
the header rest on supports, called cripple studs that transfer the load
to the ground. |
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to Knowhere |
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Page 126
- Building stability - Light wood frame construction |
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