An attempt to adapt the concept of seismic intensity to structural engineering needs

Abstract

The interest for the topic dealt with was raised by the occurrence of the destructive Vrancea earthquake of 1977.03.04, when the first strong motion record of Romania was obtained at the Building Research Institute (INCERC) Bucharest. The attempt to assess the ground motion intensity on the basis of instrumental criteria of the MSK intensity scale failed, due to strongly divergent results obtained by means of alternatively using the peak ground acceleration (PGA) and peak ground velocity (PGV) criteria. This failure was due to the fact that the (inflexible) MSK criteria relied on the implicit, non-realistic, assumption that all ground motions are characterized by a velocity / acceleration corner period of 0.5 s. A flexible Spectral Intensity Assessment System (SIAS, relying on accelerographic information, was developed by the author. This makes it possible to estimate, according to needs, global intensity, frequency related intensity, intensity averaged upon a spectral band etc. Alternative basic kinematic ground motion characteristics for global intensities and for frequency related intensities were introduced. Correlation analysis was performed. Characteristic parameters were calibrated and alternative calibrations of them are discussed. Some illustrative cases and some comments and recommendations are finally presented.