كليدواژه :
Accelerogram , Nonlinear analysis , Modification factor , Overstrength , Outrigger Bracing
چكيده فارسي :
According to developments in construction of highrise buildings both in Iran and developing
countries, more concentration and studies on seismic behaviour of these types of structures are required. Due
to a large variety of highrise buildings, current research is carried out on a special type of above mentioned
buildings, which is composed of a steel braced welded structure equipped with outrigger bracings both on
roof and mid height levels. Outrigger braced highrise structures are assumed to be a basic solution for
overturning problem by outbreaking the total outer structure of highrise buildings. This system is much more
effective than the conventional braced frame structures for buildings ranged from 40 to 60 stories high. First
the computational method for modification factor and related effective parameters are briefly described in
this research. Then a total of 8 two dimensional frames (ranging from 20 to 60 stories high) equipped with
outrigger bracings of various types both on roof and mid height levels are modelled. Then the assumed finite
element models are analysed and designed according to Iranian 2800 seismic code taking into account the
site specifications and Sa=0.25g , Sa=0.35g spectral acceleration levels. Afterwards, by using accelerograms
recorded on soil types 1,2,3 & 4 ( due to 2800 code), and after scaling them to Sa=0.25g & Sa=0.35g, a total
of 1280 linear and nonlinear Time History analyses are carried out on the above mentioned 2D models,
using Sap 2000 ver. 16.1.1 finite element software. By performing a “Modal Push-over Analysis” on each
model and by using achieved results of above mentioned analyses, the ductility and overstrength reduction
factors are computed for each model and related records. Finally, the modification factors are calculated for
both “Ultimate state” and “Working stress” design methods respectively.
