A representative seismic velocity spectrum without constant-velocity assumption

The Design Response Spectra (DRS) recommended in most modern codes are primarily based on the assumptions of three constant-sensitivity segments, i.e., the constant-acceleration, constant-velocity and constant-displacement segments at low, intermediate and long periods, respectively. These assumptions have been widely adopted and developed for several decades. However, based on recent observations from numerous recorded strong ground motions, the constant-velocity assumption fails to accurately describe the spectral characteristics in the intermediate periods (velocity-sensitive segment) for many ground motions. This study abandons the constant-velocity assumption and applies Shock-Waveform decomposition (SWD) to investigate the relationship between the Pseudo Spectral Velocity (PSV) of all SWD components and the PSV of the corresponding ground motion, based on which, a tri-linear PSV model is proposed. The proposed model, along with its compatible Pseudo Spectral Acceleration (PSA) model, is validated by PSVs and PSAs of 1370 randomly selected ground motions in Turkey. It also demonstrates superior applicability, particularly in the velocity-sensitive segment, compared to the traditional spectral models based on three constant-sensitivity assumption and other spectrum models without using constant-velocity assumption. In practical engineering applications, this model can be used to develop a more accurate design PSV with a specific return period for a given site, based on locally recorded ground motions.