The Earthquake Engineering Online Archive

The rocking spectrum and the shortcomings of design guidelines

Makris, Nicos; Konstantinidis, Dimitrios

PEER-2001/07, Pacific Earthquake Engineering Research Center, University of California, Berkeley, 2001-08, 63 pages (400/P33/2001-07)

This report is concerned with the superficial similarities and fundamental differences between the oscillatory response of a single-degree-of-freedom (SDOF) oscillator (regular pendulum) and the rocking response of a slender rigid block (inverted pendulum). The study examines the distinct characteristics of the rocking spectrum and compares the observed trends with those of the response spectrum. It is shown that the rocking spectrum complements the response spectrum as an indicator of the shaking potential of earthquakes since it reflects kinematic characteristics of the ground motions that are not identifiable by the response spectrum. The study investigates systematically the fundamental differences in the mechanical structure of the two dynamic systems of interest and concludes that rocking structures cannot be replaced by "equivalent" single-degree-of-freedom oscillators.

Available online: http://peer.berkeley.edu/publications/peer_reports/reports_2001/0107.pdf