Evaluation of Peak Ground Velocity as a “Good” Intensity Measure for Near-Source Ground Motions

This paper investigates the “goodness” of peak ground velocity as a dependable intensity measure for the earthquake shaking of civil structures. The paper stresses the importance of distinguishing between acceleration pulses and velocity pulses, and identifies two classes of near-source ground motions: those where the peak ground velocity is the integral of a distinguishable acceleration pulse and those where the peak ground velocity is the result of a succession of high-frequency, one-sided acceleration spikes. It is shown that the shaking induced by the former class is in general much more violent than the shaking induced by the latter class of motions even when motions that belong to the former class may be generated by significantly smaller-magnitude earthquakes. Building on the dimensional analysis introduced in the companion papers this paper shows that both linear and nonlinear structural responses from a variety of records which exhibit distinguishable pulses scale better with the peak pulse acceleration than with the peak pulse velocity, indicating that the peak pulse acceleration is a more representative intensity measure of the earthquake shaking. This conclusion is further supported from the response analysis of linear and bilinear single-degree-of-freedom oscillators subjected to selected records from the 1999 Chi-Chi Taiwan earthquake that exhibit unusually high and long period velocity pulses. The paper shows that these high velocity pulses alone do not impose unusual demands on most civil structures. What is more detrimental are local, distinguishable acceleration pulses that override the long period velocity pulses.