Quasi-resonance effects observed in the 1994 Northridge earthquake, and others

Sine-beat phenomena have been found in the 1994 Northridge earthquake recor ds, and they are capable of producing time-history responses and damaging q uasiresonance effects in structures. Linear, single DOF (degree of freedom) oscillators, in lieu of nonlinear, multiple DOF systems, have been found a dequate to discuss the failures of tall circuit breakers during the 1971 Sa n Fernando and the 1989 Loma Prieta quakes in California. The use of sine-b eat excitation for seismic-shaking-table tests of equipment continues to be a conservative simulation of earthquakes.