Civil Engineering Reference
In-Depth Information
10.6
DESIGN AND ANALYSIS OF ECCENTRICALLY LOADED
COLUMNS USING INTERACTION DIAGRAMS
If individual column interaction diagrams were prepared as described in the preceding
sections, it would be necessary to have a diagram for each different column cross
section, for each different set of concrete and steel grades, and for each different bar
arrangement. The result would be an astronomical number of diagrams. The number
can be tremendously reduced, however, if the diagrams are plotted with ordinates of
(instead of
P
n
) and with abscissas of (instead of
M
n
). Thus each in-
teraction diagram can be used for cross sections with widely varying dimensions. The
ACI has prepared interaction curves in this manner for the different cross section and
bar arrangement situations shown in Figure 10.14 and for different grades of steel and
concrete.
3
Two of the ACI diagrams are given in Figures 10.15 and 10.16, while Appendix A
(Graphs A.2-A.13) presents several other ones for the situations given in parts (a), (b),
and (d) of Figure 10.14.
Notice that these ACI diagrams do not include the three modifica-
tions described in the last section.
The ACI column interaction diagrams are used in Examples 10.3 to 10.7 to design or
analyze columns for different situations. In order to correctly use these diagrams, it is nec-
essary to compute the value of
c
A
g
c
A
g
h
P
n
/
f
P
n
e
/
f
(gamma), which is equal to the distance from the center
of the bars on one side of the column to the center of the bars on the other side of the col-
Figure 10.14
3
American Concrete Institute,
Design Handbook
, 1997, Publication SP-17(97), Detroit, 482 pages.
