Correlation between alternative SMD-based seismic intensity parameters and damage indices of structures

There is the tendency among engineers to disregard the importance of a seismic event’s strong motion duration (SMD) as an altogether "irrelevant" seismic parameter with regard to the destructive potential of a strong motion event. Several studies so far have proven that the use of some of the most widely used definitions of strong motion duration correlates poorly with the amount of damage a building suffers when subjected to an earthquake motion. The purpose of this paper is to numerically describe, in terms of correlation, the interdependency between different strong motion duration parameters and how those affect the overall behaviour of a reinforced concrete frame structures focussing on different type of strong motion duration definitions overturning the widely accepted notion that every definition of strong motion duration has poor correlation with the subsequent structural damage. In addition, a second set of seismic intensity parameters is introduced, combining energy-based and SMD-based parameters. The latter can be considered as seismic power parameters.
To accomplish that, a set of widely used strong motion duration parameters has been selected. Namely the Strong Motion Durations according to Trifunac/Brady (SMD T/B ), Trifunac/Novikova (SMD T/N ), Bracketed 0.03 (SMD B0.03 ), Bracketed 0.05 (SMD B0.05 ), Bracketed 0.1 (SMD B0.10 ) and McCann (SMD MC ) has been selected as the duration parameters for the strong motions under investigation. In addition, based on the above SMD parameters, several power parameters are utilized. Furthermore, in order to express the destructiveness of the seismic events a series of well documented characteristic parameters has been selected ranging from strong motion characteristics such as the Peak Ground Acceleration (PGA) value to structural damage indices such as those defined by Park/Ang (DI P/A ) and DiPasquale/Cakmak (DI DP/C ). This paper was based on the need for the quantification of the interrelationship between the aforementioned parameters and structural damage.

First of all, a set seismic accelerograms has been selected with expected damage potential from low to severe for statistical reasons. The next step was a computer supported computation of the acceleration time-histories provided us with the considered intensity parameters for each one of the utilized accelerograms.

The accelerograms above were applied on a multi-storey reinforced concrete frame building designed by the rules of EC1, EC2, and EC8. Nonlinear dynamic analyses have been performed for the reinforced concrete frame building under question for all acceleration-time histories using the IDARC v7.0 program for nonlinear inelastic analysis to obtain the structural damage indices of Park/Ang and DiPasquale/Cakmak as a mean of providing the total damage status of the structure in each case.

The numerical results show that the correlation grade between the alternative strong motion durations and the considered damage indices was from low to medium. On the other hand, the seismic power parameters based on the above alternative SMDs, show significantly increased correlation with the in this study considered damage indices.