Earthquake Response of Inelastic Systems Chap. 7
Tn = 0.5 sec and ζ = 5% to be designed for the El Centro ground motion. If this system
is designed for a strength fo = 0.919w or larger, it will remain within its linearly elastic
range during this excitation; therefore, it need not be ductile. On the other hand, if it can
develop a ductility factor of 8, it need be designed for only 12% of the strength fo required
for elastic behavior. Alternatively, it may be designed for strength equal to 37% of fo and
a ductility capacity of 2; or strength equal to 19.5% of fo and a ductility capacity of 4.
For some types of materials and structural members, ductility is difficult to achieve, and
economy dictates designing for large lateral forces; for others, providing ductility is much
easier than providing lateral strength, and the design practice reflects this. If the combination
of strength and ductility provided is inadequate, the structure may be damaged to an
extent that repair is not economical (see Fig. 7.2), or it may collapse (see Fig. 7.3).