Measurement of dynamic characteristics of structure

A new type of low frequency vibration transducer (LFVT) and the signal processing procedure used in estimation of dynamic characteristics of structure are discussed. A circuit network is adopted in the LFVT to compensate the low frequency characteristics of seismic velocity transducer with high resonant frequency, reliability and robustness, which is the primary sensor. The output characteristics of LFVT are just like those of a seismic velocity or displacement transducer with very low resonant frequency which is 1/20 to 1/50 of that of the original pick-ups. Engineering estimation methods of natural frequency and vibration mode are discussed. An improved algorithm to determine the damping ratio is put forward. In the algorithm, we use the frequency response of a second order system to fit the estimated power spectra of the signal and solve the problem of nonlinearity in this process. The algorithm has a much better precision than the generally used bandwidth method. Experiments on a railway bridge are given.