For architectural reasons or restrictions imposed by local laws, many
multistory buildings are designed with setbacks. ln this paper, the behavior of
high rise symmetric and unsymmetric setback structures under the effect of
ground motion excitation is investigated using time history dynamic analysis.
Several setback sizes and levels have been considered. Effects of setback
parameters on key response values of the Structures were examined. These
response values include fundamental translational periods of vibration,
torsional periods of vibration, setback level displacement, top story
displacement, base shear, base torsional moment and maximum input
earthquake energy. Results indicate the feasibility of obtaining satisfactory
code formulas to relate key response parameters of a setback structure to the
corresponding uniform one.