Scaling of ground motions and its implications to plan-asymmetric structures

• Change of earthquake characteristics due to scaling is correlated to scale factor.
• Such changes seldom affect torsion-induced damage of plan-asymmetric systems.
• Scale factor up to 10 may be adequate to estimate torsional amplification.
• Pair-wise scaling of record component may be ignored to reckon torsional response.
• Such trends are similar for NF and FF records regardless of target spectra (UHS/CMS).

Ground motions are often scaled to certain convenient target spectra in the response assessment of structures. While uniform hazard spectrum (UHS) is more widely used, conditional mean spectrum (CMS) is recently proposed as a more desirable target for scaling of real accelerograms. In this backdrop, the present study spectrally scales, using wavelets, a set of near-field and far-field ground motions to both the targets, viz., UHS and CMS. Relevance of a set of useful ground motion characteristics, viz., the peak ground acceleration-to-peak velocity ratio (amax/vmax), predominant period (Tp), Arias intensity (Ia), Housner intensity (IH), cumulative absolute velocity (CAV) and significant duration (Td⁎), is reviewed. Influence of ground motion scaling is discussed in terms of possible changes of such identified parameters. Seismic demand of horizontally irregular structures is assessed under both scaled and seed records recognizing strength dependent stiffness. Threshold of the scale factor, shown to have well-correlated with the change of ground motion characteristics, may be as high as ~10 to adequately estimate torsion-induced amplification in asymmetric system without any bias.