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

## Palavras-chave:

Output-Only Modal Analysis, Frequency Domain Identification Methods, MIMO, 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.