On Setting the Level of Seismic Effect in Seismic Intensity Scales and Design Standards

Abstract

It is noted in the article that the increase in peak ground acceleration (PGA) by a factor of about 1.4 proposed by seismologists in a project of seismic intensity scale clearly reflects the lessons learned from earthquakes of the past. However, the use of suggested PGA values in the design codes and standards requires modification of the codes and standards themselves, as well as differentiated approach to defining the design level of PGA. Engineers should consider the dependence of the design PGA on the oscillation periods of structures, whereas seismologists should differentiate the PGA value depending on the prevailing period of the seismic effect. Transition to the new seismic scale affects the design and maximum design earthquakes differently. The intensity of a design earthquake for objects of massive structure does not exceed VII on the MSK scale, and in this aspect the new seismic scale does not differ considerably from the existing one. For maximum design earthquakes, PGA increases significantly, but the criterion of seismic resistance changes from acceleration of the structure to the work of plastic deformation forces. In this case, possible destruction depends little on PGA, but rather on such energy seismic effect characteristics as the Arias intensity, absolute cumulative velocity, and seismic energy density. A correct approach to calculation when carrying out the performance-based design and transition to the new intensity scale would not lead to higher costs for most buildings and structures. Moreover, if one does not use the new scale, transition to modern methods of performance-based design will be impossible.