Mohammdreza Azimzadegan - Islamic Azad University of Science and Research of Fars
Mahdiye Shaygan - Shiraz University of Technology, Shiraz, Iran.
MohammadAli Hadianfard - Shiraz University of Technology, Shiraz, Iran.

According to Iranian code, Structure components should be designed for the forces caused by wind or seismic load, whichever is greater. Increase in the height to size ratio of a structure causes the impact of the wind loadfluctuations on the structure takes on further significance. Additionally, setback at upper stories results in suddenreduction of structural stiffness and mass, subjecting its dynamic properties to abrupt changes. In these conditions, windforces which are estimated using static and dynamic analyses, may lack sufficient accuracy. In this research, lateralforces of wind are determined using static and dynamic analyses according to Iranian code and time history analysis. Also the forces caused by earthquake are determined by static analysis. These analyses were carried out on 10, 15-, and20 stories regular and irregular (set-back) structures. The lateral forces caused by wind and seismic loads werecompared together and the results were presented as story shear and force distribut ion in columns. The results show thatshear base which is calculated by time history analysis in the 15-story structures is more than the shear base caused by earthquakes. whereas, the shear caused by earthquakes in top stories are more than the shear caus ed by wind load.

Geometric irregularity, wind load, seismic load, time history analysis