Azadeh Ahmadi - M.Sc. Student at Kharazmi University, Faculty of Engineering, Tehran, Iran
Masoud Azhdarifar - M.Sc. at Kharazmi University, Faculty of Engineering, Tehran, Iran
Afshin Meshkat-Dini - Assistant professor at Kharazmi University, Tehran, Iran

In this article, a study of the effects caused by the changes in the modulation of the frame structure on the performance of the lateral resisting systems with a bundled-tube structure is presented which is based on the assessment of the nonlinear dynamic response under near and far field records. Three different modulations having bundled-tube structures with an orderly plan are chosen for two 10-story and 20-story buildings and are designed according to the Iranian seismic code 2800, fourth edition and also the Iranian National Building Code (Steel Structures - Division 10). Moreover, in this research, the main criterion in choosing near field records for nonlinear time history analyses has been the presence of a singular coherent pulse with a long period and high amplitude accompanied with multiple pulse-like waveforms in the time history of ground motion. The analytical assessment of the results of this research has been done with a major focus on modulation changes in the structure's height and its effect on the fluctuation of seismic response parameters, such as lateral displacement and story drift which are of notable importance in the designing process. It has been observed that subject to near field records contain velocity pulses, the drift response parameter has relatively similar amounts in the 10-story building and its changes become more apparent as the height increases.

keletal modulation, nonlinear dynamic analysis, steel frame, bundled tube, velocity pulse