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Earthquakes and Structures
  Volume 12, Number 4, April 2017, pages 437-448

Identifying stiffness irregularity in buildings using fundamental lateral mode shape
A. R. Vijayanarayanan, Rupen Goswami and C. V. R. Murty

    Soft or extreme soft storeys in multi-storied buildings cause localized damage (and even collapse) during strong earthquake shaking. The presence of such soft or extremely soft storey is identified through provisions of vertical stiffness irregularity in seismic design codes. Identification of the irregularity in a building requires estimation of lateral translational stiffness of each storey. Estimation of lateral translational stiffness can be an arduous task. A simple procedure is presented to estimate storey stiffness using only properties of fundamental lateral translational mode of oscillation (namely natural period and associated mode shape), which are readily available to designers at the end of analysis stage. In addition, simplified analytical expressions are provided towards identifying stiffness irregularity. Results of linear elastic time-history analyses indicate that the proposed procedure captures the irregularity in storey stiffness in both low- and mid-rise buildings.
Key Words
    modal analysis; mass participation; open storey; soft storey; storey stiffness
Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600036, India

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