EXPERIMENTAL INVESTIGATION OF FRICTION-BASE ISOLATION

Structural vibration control is one of the main goals of civil enginee rs involved in the structural safety and reliability of buildings situ ated in regions susceptible to earthquakes. Friction-base isolators ha ve been adopted as a means of passive control. The purpose of this exp erimental investigation is to measure the response statistics in the p resence of base friction and other friction sources. The experimental model emulates a single-floor building supported on four leaf springs, subjected to band limited random excitation. Two different types of m odel base are considered, a friction base and a Frictionless base. In both cases, friction can also be applied at two sides of the models ma in mass against the direction of its motion. Excitation and response t ransducer signals are processed to estimate excitation and response st atistics in the presence and in the absence of top mass friction. Meas ured statistics include mean squares, autocorrelation functions, power spectra, and probability density functions. The dependence of the mea n square response on the excitation level in the presence of friction reveals linear and nonlinear regimes, as well as a drift in the respon se due to dry friction. Above a certain excitation level the response- excitation relationship displays nonlinearity. A transition from narro w band to wide band response spectra is observed when friction is appl ied to the systems top mass. Analytical and Monte Carlo simulation res ults are compared with those measured experimentally based on a consta nt friction force. (C) 1997 Elsevier Science Ltd.