A design spectrum model for flexible soil sites in regions of low-to-moderate seismicity

• Published in: Soil dynamics and earthquake engineering (1984) 2017-01, Vol.92, p.36-45
• Main Authors: Tsang, H.H., Wilson, J.L., Lam, N.T.K., Su, R.K.L.
• Format: Article
• Language: English
• Subjects: Amplification; Behavior; Building codes; Building design; Building foundations; Code; Codes of Practice; Collapse; Computer applications; Design engineering; Design spectrum; Displacement; Earthquakes; Empirical analysis; Frequency domains; Resonance; Risk; Seismic phenomena; Seismicity; Seismology; Site factor; Soil amplification; Soil sciences; Soils; Structural design; Structural engineering; Studies
• ISSN: 0267-7261; 1879-341X
• DOI: 10.1016/j.soildyn.2016.09.035

Design spectrum (DS) models in major codes of practice for structural design of buildings typically stipulate empirical site factors for each of the five, or six, site classes. Although the phenomenon of resonant like amplification behaviour of the structure caused by multiple wave reflections is well known, the potentials for such periodic amplification behaviour are not explicitly considered in code models. This is partly because of expert opinion that such effects are very “localised” in the frequency domain and can be suppressed readily by damping. However, investigations into the risk of collapse of non-ductile, and irregular structural systems, common in regions of low-to-moderate seismicity, revealed the extensive influence of periodic base excitations on flexible soil sites (with initial small-strain natural period Ti >0.5s). In this paper, an alternative DS model which addresses the important phenomenon of soil resonance without the need of computational site response analysis of the subsurface model of the site is introduced. •Displacement demand on structure is governed by resonant-like soil-amplification.•Inconsistencies amongst design spectrum models in seismic codes are highlighted.•A new design spectrum model featuring resonant-like soil-amplification is proposed.•The model is for structures which absorb little energy to suppress resonance.•The proposed model is most suited to regions of low-to-moderate seismicity.