10-10-2014, 01:58 PM
Since the inception of the inclusion of the aspect of safety of the structures
against the earthquake ground motion in the structural design, the available
literature shows that not much study of the influence of the shape in plan has
been taken into consideration.
About three and a half decades ago, the first thought to this consideration
warned that an asymmetric plan shape might lead to torsional vibrations due to
eccentricity between mass centre and the shear centre.
Biggs and Dowrick did a superficial study on asymmetrically planned buildings.
Dowrick suggested that an asymmetrically planned shape can best be avoided
rather than designed for. But a symmetrically planned shape is very difficult to
achieve due to practical limitations such as shape of plot, soil conditions, Purpose
of the building etc.
In the present study, aspects of the shape of the structure in plan have been
studied in depth. The significant observations of the asymmetrically planned
buildings undergoing torsional vibrations has been mentioned in the later
chapter 4, Also influence of the eccentricity between mass center and the shear
centre has been studied for various shapes of buildings.
Influence of period and aspect ratio on the response of rectangular building with
two d.o.f and three d.o.f is also studied.
In this study, the record of EL-Centro earthquake, May 1940, has been used for
the analysis.