The “strength” of an earthquake ground motion is often quantified by an intensity measure (IM), such as peak ground acceleration or spectral acceleration at a given period. This IM is used to quantify both the rate of occurrence of future earthquake ground motions (hazard) and the effect of these ground motions on the structure (response). In this report, intensity measures consisting of multiple parameters are considered. These intensity measures are termed vector-valued IMs, as opposed to the single parameter, or scalar, IMs that are traditionally used. Challenges associated with utilizing a vector-valued IM include choosing an effective vector of IM parameters, computing the ground motion hazard associated with the vector IM, and estimating structural response as a function of a vector of parameters. Contributions are made in all of these areas.
A newly proposed intensity measure of particular interest consists of spectral acceleration plus a parameter termed epsilon. Epsilon (defined as a measure of the difference between the spectral acceleration of a record and the mean of a ground motion prediction equation at the given period) is found to have
significant ability to predict structural response. Epsilon is shown to be an indicator of spectral shape, explaining its effectiveness. Neglecting the effect of epsilon typically leads to conservative estimates of structural performance.
In this report, it is shown that vector-valued intensity measures can be used to eliminate bias in structural performance assessments, as well as increase the efficiency of structural response prediction (which can lead to a reduction in the number of dynamic analyses required to estimate response with a given precision). One of the intensity measures is also shown to be useful for characterizing the effect of near-fault ground motions that contain a velocity pulse—a class of ground motions whose effects are poorly captured by current intensity measures. Findings regarding effective intensity measures have also been
used to identify new methods for selecting ground motions for use in dynamic analysis.
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