On the suitability of shear-wall systems for building structures in seismic zones

Assessment of structural performances during past earthquakes demonstrates that plan irregularity is one of the most frequent sources of severe damage, since it results in floor rotations in addition to floor translations. Comprehension of such a behaviour, in general refferred to as torsional response, is therefore of great interest not only with reference to the elastic but also inelastic range of behaviour, as the ability of structures to resist strong earthquakes depends upon their ductility and capacity for energy dissipation. Plan irregularity may be a consequence of plan asymmetric distributions of stiffness and strength among vertical resisting elements, but it is also frequently due to asymmetric distribution of mass over the floor slabs. Whatever the source of plan-wise uneveness may be, the initial stage of the design process is more important than application of code specifications or implementation of refined numerical models, being a seismically correct conceptual design crucial in determining the behaviour and the earthquake vulnerability of plan-irregular buildings. In this paper, the suitability of shear-wall systems for building structures in seismic zones is discussed. In the linear range of behaviour the use of a shear-wall structures, especially if located on the building perimeter, is desirable since the large torsional stiffness given by such systems results in reducing torsional effects. Nevertheless, shear-wall systems may be very insidious in the non linear range of behaviour since significant amplifications of floor rotations can occur as a consequence of the yielding of one or few resisting elements.