Civil Engineering Reference
In-Depth Information
Pennsylvania Southern
Expressway, Philadelphia,
Pennsylvania. (Courtesy of
Economy Forms
Corporation.)
c
.
reaches its maximum compression
0.85
f
This situation is called the
balanced
loading condition
.
(e)
Large moment with small axial load
. If the eccentricity is further increased, fail-
ure will be initiated by the yielding of the bars on the tensile side of the column
prior to concrete crushing.
(f)
Large moment with no appreciable axial load
. For this condition, failure will
occur as it does in a beam.
10.2
THE PLASTIC CENTROID
The eccentricity of a column load is the distance from the load to the
plastic centroid
of
the column. The plastic centroid represents the location of the resultant force produced by
the steel and the concrete. It is the point in the column cross section through which the re-
sultant column load must pass to produce uniform strain at failure. For locating the plastic
centroid, all concrete is assumed to be stressed in compression to and all steel to
f
y
in compression. For symmetrical sections, the plastic centroid coincides with the centroid
c
0.85
f
