Civil Engineering Reference
In-Depth Information
F
i g u r e
14.4 Frame method of analysis.
where
b
= widthofwall, in
d
equiv
=
equivalent depth, in
Once the equivalent frame member sizes are determined, they are put into the com-
puter model at their respective neutral axis locations. The uniform gravity loads above
the outer sections of the piers are replaced as concentrated loads,
P
L
and
P
R
, at the upper
joints of the frame at the neutral axis locations. The factored uniform load
w
of the load
combination being examined should include the dead load of the wall or frame.
Computer frame members are shown as single lines located at their neutral axis
locations. The lateral forces are usually applied at the neutral axis of the beam and/or
column sections when using plane frame programs. However, the lateral forces that are
actually applied to walls typically occur at the top plate, which causes a vertical offset
from the neutral axis. The computer model shown on the left side of Fig. 14.5 accounts
for this offset by extending the pier sections up to the top plate of the wall so that the
lateral forces can be applied at that location. The base of the pier sections can be mod-
eled with the classic fixed node option provided in the computer program, or alter-
nately modeled as shown at the bottom of the figure, which will directly provide the
anchor forces at the base of the wall. The anchor forces can also be calculated by simple
statics, combining the axial force with the couple forces caused by the moment. For
example, the tension and compression reaction forces applied to the bottom of the right
pier are
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