Abstract:
This paper describes the study of the metrological quality of the excitation force in
the context of force vibration test of concrete dams. For this purpose, a measurement
uncertainty evaluation was performed, based on available probabilistic information about the
input quantities – rotation frequency, mass, radial position, dimension, diameter and density of
the generator’s rod – which support the determination of the excitation force in an eccentric
masses vibration generator, used by LNEC in concrete dam’s field observation. The
uncertainty propagation from the input quantities to the output quantity was performed by a
Monte Carlo method, considering the mathematical model used for the determination of the
excitation force. Two experimental cases were studied: (A) the use of five weights in the
generator in the frequency range of 1 Hz up to 6 Hz; and (B) the use of a single weight in the
generator in the frequency interval comprised between 5 Hz and 15 Hz. In the first case, the
excitation force estimates and expanded measurement uncertainties (considering a 95 %
confidence interval) varied between 3.55 kN ± 0.14 kN and 127.68 kN ± 0.91 kN, being
rotation frequency the major contribution for the obtained dispersion of force values. In the
second case, the excitation force estimates and expanded measurement uncertainties varied
between 16.71 kN ± 0.25 kN and 150.4 kN ± 1.8 kN, being the generator’s rod diameter the
main contribution for the output measurement uncertainty. The obtained knowledge is essential
to assure confidence and rigorous knowledge about the applied excitation force, namely, in
extreme situations near dynamical structural safety limits of the observed concrete dam and of
the testing equipment