OUTPUT-ONLY MODAL PARAMETER IDENTIFICATION OF A RECTANGULAR BEAM USING MIMO AND SIMO TESTS

Resumo

The dynamic behavior of structures can be evaluated through modal parameters, which can
be obtained experimentally, and used to solve vibration problems, in sensitivity analyses, in structural
modification, for numerical and experimental model correlation, for updating numerical model, for
structural health monitoring, etc. The present work aims to identify the modal parameters (natural
frequencies, damping ratios and vibration modes) of a rectangular aluminum beam suspended in the air,
simulating the “free-free” boundary condition. The rectangular beam was instrumented with 09
accelerometers arranged equidistantly along the length. Two types of tests were performed: (i) the
multiple reference impact testing (MRIT), which simulates MIMO (multiple input/multiple output) test;
(ii) the SIMO (single input/multiple output) test, which generates responses in the 09 accelerometers
due to the impacts in 01 degree of freedom. Modal parameters were identified using only the vibration
responses, through two frequency domain techniques: Enhanced Frequency Domain Decomposition
(EFDD) and Frequency-Spatial Domain Decomposition (FSDD). Results showed that the average
difference in natural frequencies estimation with the EFDD technique, using MIMO and SIMO tests,
was 0.25%, a low and acceptable percentage. When comparing EFDD (MIMO test), FSDD (SIMO test)
and FEM model results, the average differences in natural frequencies estimation are 0.33% and 1.63%,
respectively. According to the results, both EFDD and FSDD methods can be used to identify the modal
parameters, with similar results, using either the MIMO or SIMO tests. As the SIMO test demands less
time, it becomes a fast alternative for modal identification of structures.