Civil Engineering Reference
In-Depth Information
Figure 14.7
beam to collapse. The arrangement of plastic hinges, and perhaps real hinges that permit
collapse in a structure, is called the
mechanism
. Parts (b) of Figures 14.6, 14.7, and 14.8
show mechanisms for various beams.
Plastic Analysis by the Equilibrium Method
To analyze a structure plastically, it is necessary to compute the plastic or ultimate mo-
ments of the sections, to consider the moment redistribution after the ultimate moments
develop, and finally to determine the ultimate loads that exist when the collapse mecha-
nism is created. The method of plastic analysis known as the
equilibrium method
will be
illustrated in this section.
As the first illustration, the fixed-end beam of Figure 14.9 is considered. It is desired
to determine the value of
w
n
, the theoretical ultimate load the beam can support. The max-
imum moments in a uniformly loaded fixed-end beam in the elastic range occur at the
fixed ends, as shown in the figure.
Figure 14.8
