Experimental investigation of friction-base isolation

Structural vibration control is one of the main goals of civil engineers involved in the structural safety and reliability of buildings situated in regions susceptible to earthquakes. Friction-base isolators have been adopted as a means of passive control. The purpose of this experimental investigation is to measure the response statistics in the presence 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 model base are considered, a friction base and a frictionless base. In both cases, friction can also be applied at two sides of the models main mass against the direction of its motion. Excitation and response transducer signals are processed to estimate excitation and response statistics in the presence and in the absence of top mass friction. Measured statistics include mean squares, autocorrelation functions, power spectra, and probability density functions. The dependence of the mean square response on the excitation level in the presence of friction reveals linear and nonlinear regimes, as well as a drift in the response due to dry friction. Above a certain excitation level the response-excitation relationship displays nonlinearity. A transition from narrow band to wide band response spectra is observed when friction is applied to the systems top mass. Analytical and Monte Carlo simulation results are compared with those measured experimentally based on a constant friction force.