Procedimento experimental para avaliação do fator de amortecimento em estruturas

Abstract

Nowadays, the importance of dynamic analysis on structures has been increasing parallel to new building technologys development. Growing knowledge on materials behavior and the optimization of their use has lead to the construction of even more slender structures. Therefore, structures natural frequencies have been decreasing, approaching to the frequency due to rhythmic activities, industry rotative machines or, for example, stadium crowd movement. Once the structures solicitation is closer to resonance, displacements and acceleration are intensified, which may exceed recommended limits and cause peoples discomfort.Damping has a large importance on controlling this phenomenon, by dissipating the energy associated to structural vibration. Concerning on a free vibration, the energy loss of the damping system causes the vibration amplitude decrease, while attenuates structures displacement and acceleration peaks on forced vibration. Thus, accurate estimation onstructural damping factor provides efficient structural design and offers safety and peoples comfort as well. The aim of this work is to obtain experimental values for structural damping factors and to evaluate the reliability of the applied methodology. Several types of dynamic tests were performed over three structures floors to obtain the structural response. Measurements were done by accelerometers. In order to excite the floors, following tests and devices were used: a mechanical exciter, the impact of a falling steel block, the heel drop test, and the impact of a jumping person. The structural response graphics at the time domain regarding the main natural frequencies were obtained using suitable bandpass filters. Then, damping factor values were obtained using the Logarithmic Decrement Method, the Half Amplitude Method and the Curve Fitting Method as well. These signals were also presented in the frequency domain. Once the structures natural frequencies were defined they were used to fit numeric simulation using finite element software.