EVALUATION OF HIGHER MODES EFFECTS IN ESTIMATION OF SEISMIC RESPONSE PARAMETERS OF TALL HYBRID MEGA ZIPPER SKELETONS

This research investigates the analytical capability and effectiveness of modal pushover method (MPA) in predicting the important responses of high-rise steel buildings subjected to both far and near-field earthquake records. This was performed based on comparing the predicted values by MPA with the corresponding parameters obtained through comprehensive nonlinear dynamic time history analyses (NLTH). For this purpose, three 30-story structural models with rigid castled tube resistant skeleton were selected and designed. The first studied model is classified as the basic structure with a castled tube structural system and is identified by the CT symbol. The second and third studied models are introduced by setting two different multi-level configurations of large scale zipper elements in the structure of the basic model. The large scale zipper elements are connected to one or two perimeter columns at the first story level and introduced with the symbols MZCT-1C and MZCT-2C, respectively.The reason for setting a multi-story arrangement of large scale zipper elements is preventing the formation of expanded plastic mechanism and block the occurrence of possible lateral-torsional buckling in the columns of lower-stories. The connection of the large scale zipper elements to the columns is considered flexurally rigid. The plan and configuration of the studied structures are shown in Figure 1. The studied structures were loaded and designed based on the Iranian national building codes (issues six and ten) as well as the Standard 2800 (fourth edition). The assigned performance profiles of plastic hinges for describtion of non-linear behavior of structural elements have been adapted from the reports FEMA 356 and 440. All of the nonlinear analyses were conducted through SAP2000 software. In this research, the seismic tremors were selected in an ensemble of twelve earthquake records, including six far-field and six near-field ground motions which contain forward directivity effects. The distance of recording stations related to the aforementioned near-field ground motions is not more than 20 kilometers away from the fault rupture plate. The main criterion in choosing these records is the existence of coherent pulses and high-amplitude spikes in the velocity time history caused by powerful rupture directivity process (Mukhopadhyay & Gupta, 2013, Vafaee & Saffari, 2016).

کلیدواژه ها:

Tall building ، Higher modes ، Modal pushover ، Modal participation ، Nearfield record