Ground motion intensity measures for performance-based earthquake engineering

A critical issue in the probabilistic framework for performance-based earthquake engineering is the choice of ground motion intensity measure(s). In an effort to identify optimum intensity measure(s), a comprehensive parametric statistical study based on 881 earthquake record components was conducted to identify the correlation between (1) seismological variables (SV’s) and traditional ground motion intensity measures (IM’s), and (2) various nonlinear SDOF response parameters indicative of damage. A set of new nonlinear SDOF-based ground motion intensity measures is defined and proposed to complement the elastic spectral acceleration at the initial fundamental period (T0) of the structure. The correlation performance of the new intensity measures is compared to that of traditional intensity measures. The new intensity measures are shown to be efficient in reducing the dispersion of nonlinear single-degree-of-freedom (SDOF) response parameters across a wide range of initial periods T0 and strength levels. A few alternative vectors of optimum ground motion intensity measures are proposed, which consist of the 5 percent damped elastic spectral acceleration at the initial fundamental period of the structure as the primary intensity measure complemented by one or two newly proposed nonlinear SDOF-based ground motion intensity measures as secondary intensity measures. Proceedings of the Ninth International Conference on Applications of Statistics and Probability in Civil Engineering (ICASP9), San Francisco, USA, July 6-9, 2003 where = number of causative faults; = mean annual rate/frequency of occurrence of earthquakes with magnitudes greater than a lower-bound threshold value, , on fault i. Functions and denote the probability density functions (PDF) for magnitude ( ) and site-to-source distance ( ), respectively, given the occurrence of an earthquake on fault i. The conditional probability of exceeding the threshold value z given and corresponds to one minus the cumulative distribution function (CDF) of the attenuation (or predictive relationship of given seismological variables M and R) (Abrahamson and Silva, 1997; Campbell, 1997). 1.2 Probabilistic seismic demand hazard analysis The mean annual frequency, , of a given structural response parameter (or engineering demand parameter EDP) exceeding a specified threshold value d is obtained by convolving the probability distribution of the EDP in question conditioned on the seismological variables M and R and the ground motion intensity measure IM, , with the seismic hazard, , as