(1) Phase Plane Solution. This is a graphical method of solution
in which it is assumed that the structural system can be represented by a
single degree-of-freedom system. It is very useful in predicting maximum
deflections, velocities, and times to maxima for response in the elastic or
elasto-plastic range. However, it can be very cumbersome for predicting
response in the plastic range. For a complete description of this method,
the designer is referred to the report by Keenan.
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