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Earthquakes and Structures
  Volume 19, Number 3, September 2020, pages 197-214

Collapse assessment and seismic performance factors in tall tube-in-tube diagrid buildings
Alireza Khatami, Mahdi Heshmati and Ali Akbar Aghakouchak

    Diagrid structures have been introduced as a fairly modern lateral load-resisting system in the design of high-rise buildings. In this paper, a novel diagrid system called tube-in-tube diagrid building is introduced and assessed through pushover and incremental dynamic analyses. The main objectives of this paper are to find the optimum angle of interior and exterior diagrid tube and evaluate the efficiency of diagrid core on the probability of collapse comparing to the conventional diagrid system. Finally, the seismic performance factors of the proposed system are validated according to the FEMA P695 methodology. To achieve these, 36-story diagrid buildings with various external and internal diagonal angles are designed and then 3-D nonlinear models of these structures developed in PERFORM-3D. The results show that weight of steel material highly depends on diagonal angle of exterior tube. Adding diagrid core generally increases the over-strength factor and collapse margin ratio of tall diagrid buildings confirming high seismic safety margin for tube-in-tube diagrid buildings under severe excitations. Collapse probabilities of both structural systems under MCE records are less than 10%. Finally, response modification factor of 3.0 and over-strength factor of 2.0 and 2.5 are proposed for design of typical diagrid and tube-in-tube diagrid buildings, respectively.
Key Words
    diagrid system; pushover; Incremental Dynamic Analysis (IDA); collapse margin ratio; FEMA P695; high-rise building
Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran

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