Bi-linear displacement response spectrum model for engineering applications in low and moderate seismicity regions

The second corner period has become a feature in the design response spectrum provisions in some major codes of practices with the general notion that the higher the value of the corner period the higher the design peak displacement demand value. Expressions recommended in the literature for determining the value of the corner period are very diverse. Ambiguities with the definition of the corner period and the manner in which its value is calculated as illustrated in the paper may well be contributors to the diversity. A generalized response spectrum model in the displacement format for providing predictions on rock sites in low and moderate seismic regions is proposed in this paper. The flat part of the spectrum of the bi-linear form defining the peak displacement limit is first constructed in accordance with functions of magnitude and distance of the earthquake (and is independent of the second corner period). Significantly, the displacement limits associated with local earthquake scenarios considered in this paper on soft rock/stiff soil sites were generally less than 100 mm. The sloping part of the spectrum is then determined in accordance with the estimated second corner period value. The generic predictive capability of the model spectrum and its robustness due to the way it is constructed make the model distinctive. Importantly, the proposed model (based on 5 s cut-off period limit) is suitable for applications where equivalent linearization techniques are employed to obtain approximate estimates of inelastic displacement demand in buildings structures.

► Model for predicting drift demand is proposed for areas of low-moderate seismicity. ► Peak displacement demand is denoted as RSDmax and corner period as T2 in the model. ► Prediction of RSDmax is generic because of its low inter-regional variability. ► Model has been rigorously evaluated involving database of earthquake records. ► Model has immense engineering values in conditions of moderate ground shaking.