Civil Engineering Reference
In-Depth Information
for just one column, however, is quite tedious. Imagine the work involved in a design
situation where various sizes, concrete strengths, and steel percentages need to be consid-
ered. Consequently, designers resort almost completely to computer programs, computer-
generated interaction diagrams, or tables for their column calculations. The remainder of
this chapter is concerned primarily with computer-generated interaction diagrams such as
the one in Figure 10.10. As we have seen, such a diagram is drawn for a column as the
load changes from one of a pure axial nature through varying combinations of axial loads
and moments and on to a pure bending situation.
Interaction diagrams are obviously useful for studying the strengths of columns with
varying proportions of loads and moments. Any combination of loading that falls inside
the curve is satisfactory, whereas any combination falling outside the curve represents
failure.
If a column is loaded to failure with an axial load only, the failure will occur at point
A
on the diagram (Figure 10.10). Moving out from point
A
on the curve, the axial load ca-
pacity decreases as the proportion of bending moment increases. At the very bottom of
the curve, point
C
represents the bending strength of the member if it is subjected to mo-
ment only with no axial load present. In between the extreme points
A
and
C
, the column
fails due to a combination of axial load and bending. Point
B
is called the
balanced point
and represents the balanced loading case, where theoretically a compression failure and
tensile yielding occur simultaneously.
Figure 10.10
Column interaction diagram.
