REAL AND FICTITIOUS ELASTIC AXES OF MULTISTORY BUILDINGS - THEORY

The application of the 'equivalent' static method for the seismic desi gn of asymmetric buildings presupposes the existence of an elastic axi s-the geometrical locus of the elastic centres of the floors-so as to identify the eccentricity of the seismic loads. But, while in single-s torey buildings the elastic centre is always defined and has determine d static properties, in multi-storey buildings the said properties are not, in general, identified and the definition of the elastic axis is , in general, impossible. In this paper, which is the first of two com panion papers, we first proceed to the analysis of the cases of existe nce or non-existence of an elastic axis and of building's principal be nding planes, according to research data of the last ten years. Follow ing this stage, and based on the building's 'optimum torsion' criterio n, a fictitious elastic axis is defined for every case of a regular-in -elevation building. This axis may play the same role as the real elas tic axis during the application of the 'equivalent' static method. (C) 1998 John Wiley & Sons, Ltd.