Civil Engineering Reference
In-Depth Information
Washington Redskins Stadium. (Courtesy of EFCO.)
sile steel on the other side has a strain of
f
y
/
E
s
. Although it is easily possible to prevent a
balanced condition in beams by requiring that tensile steel strains be kept well above
such is not the case for columns. Thus for columns it is not possible to prevent sudden
compression failures or balanced failures. For every column there is a balanced loading
situation where an ultimate load
P
bn
placed at an eccentricity
e
b
will produce a moment
M
bn
, at which time the balanced strains will simultaneously be reached.
At the balanced condition we have a strain of
f
y
E
s
,
0.003 on the compression edge of the
0.00207 in the tensile steel. This in-
formation is shown in Figure 10.7. The same procedure used in Example 10.2 is used to
find
P
n
column and a strain of
f
y
/29
10
3
60/29
10
3
559.7 ft-k.
The curve for
P
n
and
M
n
for a particular column may be extended into the range
where
P
n
becomes a tensile load. We can proceed in exactly the same fashion as we did
when
P
n
was compressive. A set of strains can be assumed, and the usual statics equations
can be written and solved for
P
n
and
M
n
. Several different sets of strains were assumed for
504.4 k and
M
n
Figure 10.7
