SEISMIC PERFORMANCE OF STEEL TALLBUILDINGS WITH OUTRIGGER SYSTEMIN NEAR FAULT ZONES

As much as a building becomes taller, the stiffness of the structure plays a more important role than the other structural parameters of building. To reach the desirable stability for tall towers, it is necessary to increase the stiffness of structure. One of the best available ways to maintain the lack of stiffness is to use outrigger belt trusses between external columns. For high-rise buildings, particularly in the seismic active zones, this bracing system can be added to the structure. The main objective of this paper is to study the performance of a continuous three-story outrigger system which is used in a tall braced frame steel skeleton. For this purpose, three 30-story buildings with different configurations of outrigger systems have been selected and designed. The structural models have been designed according to the Iranian seismic code 2800 (3rd edition). For performing the non-linear time history analyses, the particular criterion for the selected strong earthquake records is the appearance of a coherent pulse or multiple pulse features in the velocity time history concerning with high amplitude factors and long period. The illustrated results of this research show that the response parameters of the studied structures subjected to near-field earthquake records are greater than those of far-field ones.Furthermore, the outrigger systems increase the base shear but decrease the drift and lateral deflection significantly. The reduction values in the lateral deflection are about 40% and 50% respectivelyfor the model with single top outrigger and the model with mid and top outriggers,respect to the model without any outrigger under influencing of strong records. Furthermore, the other response parameters would remain in the acceptable performance domain. Yet, an intensive concentration of the axial stress resultants were resulted in the perimeter column elements which would be caused by the action of outrigger systems.