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Simplified elastic design checks for torsionally balanced and unbalanced low-medium rise buildings in lower seismicity regions

  • Lam, Nelson T.K. (Department of Infrastructure Engineering, The University of Melbourne) ;
  • Wilson, John L. (Faculty of Science, Engineering and Technology, Swinburne University of Technology) ;
  • Lumantarna, Elisa (Department of Infrastructure Engineering, The University of Melbourne)
  • Received : 2016.02.08
  • Accepted : 2016.10.11
  • Published : 2016.11.25

Abstract

A simplified approach of assessing torsionally balanced (TB) and torsionally unbalanced (TU) low-medium rise buildings of up to 30 m in height is presented in this paper for regions of low-to-moderate seismicity. The Generalised Force Method of Analysis for TB buildings which is illustrated in the early part of the paper involves calculation of the deflection profile of the building in a 2D analysis in order that a capacity diagram can be constructed to intercept with the acceleration-displacement response spectrum diagram representing seismic actions. This approach of calculation on the planar model of a building which involves applying lateral forces to the building (waiving away the need of a dynamic analysis and yet obtaining similar results) has been adapted for determining the deflection behaviour of a TU building in the later part of the paper. Another key original contribution to knowledge is taking into account the strong dependence of the torsional response behaviour of the building on the periodic properties of the applied excitations in relation to the natural periods of vibration of the building. Many of the trends presented are not reflected in provisions of major codes of practices for the seismic design of buildings. The deflection behaviour of the building in response to displacement controlled (DC) excitations is in stark contrast to behaviour in acceleration controlled (AC), or velocity controlled (VC), conditions, and is much easier to generalise. Although DC conditions are rare with buildings not exceeding 30 m in height displacement estimates based on such conditions can be taken as upper bound estimates in order that a conservative prediction of the displacement profile at the edge of a TU building can be obtained conveniently by the use of a constant amplification factor to scale results from planar analysis.

Acknowledgement

Grant : Collapse Assessment of Reinforced Concrete Buildings in Regions of Lower Seismicity

Supported by : Australian Research Council (ARC)

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