Designing inelastic geotechnical systems on the basis of single design elastic response spectrum

One of the greatest uncertainties in earthquake-resistant design is the proper selection of ground motions to be used as excitations. The universally accepted way to confront this is the establishment of the design linear elastic response (LER) spectrum as the basis of excitation for all types of man-made and natural systems - elastic and inelastic. By demonstrating that the critical ground motions are fundamentally different for elastic and inelastic systems, the paper challenges the usefulness of the concept of design LER spectrum for strongly inelastic geotechnical systems, as well as for specific inelastic structural systems such as base-isolated structures on friction bearings. While dogmatically respecting such a spectrum may be appropriate for elastic or mildly-inelastic systems, it is shown to be of secondary relevance for strongly inelastic systems, which are vulnerable to acceleration and velocity pulses of long duration, as the late Professor Vitelmo Bertero had demonstrated 40 years ago. Attributed primarily to forward-rupture directivity effects in near fault recordings and somewhat less frequently to fling steps appearing close to dip-slip and strike-slip faults emerging on the ground surface, such acceleration and/or velocity pulses are not always adequately reflected in current design elastic spectra. It is also shown that to such motions, highly-asymmetric geotechnical systems like slopes and retaining walls may exhibit a striking sensitivity not only to near-fault characteristics of excitations but also to the polarity of motions, an outcome of inelasticity which cannot be anticipated on the basis of current design LER spectra.

Automated summary

This paper discusses the uncertainty in selecting ground motions for earthquake-resistant design and the significance of the design linear elastic response spectrum. It points out that while adhering to the design LER spectrum may be suitable for elastic or mildly inelastic systems, it may be less relevant for strongly inelastic systems.