Interest on the dynamic behavior of latticed structures has been increased in the latest
decades in Brazil since some accidents with total collapse of some structures, due to
excessive vibration, have been occurred in its different regions. In the Amazon region,
for instance, where these latticed structures overcome great obstacles such as the
rainforest and large rives crossings, cases of collapse of latticed structures have been
also reported. This master thesis focuses on the study of the modal behavior of latticed
steel structures subjected to ambient vibrations caused by unknown excitation forces.
Two study cases are presented: in the first, the modal behavior of a steel overhead
transmission line tower is investigated; in the second case, the modal behavior and
comfort level of a steel bridge is studied. The study of this last case aims at
investigating the level of comfort of the bridge under ambient vibration, caused by wind
gusts and vehicle traffic, according to the Brazilian standard NBR 8800 (1986). In both
study cases, experimental and theoretical dynamic analyzes were performed to extract
the modal parameters of theses structures. In the experimental stage, both structures
were monitored using a set of low frequency accelerometers as well as a data
acquisition system suitable for vibration tests of civil engineering structures. Since it is
very difficult to measure the magnitude of ambient excitation forces, two stochastic
subspace identification methods known as SSI-DATA and SSI-COV were employed to
extract the modal parameters of the analyzed structures from response data collected in
the vibration tests. Among all activities performed in this stage, a Graphical User
Interface (GUI) toolbox in Matlab® platform was developed. In this toolbox, the above
mentioned stochastic methods were implemented to extract modal parameters of civil
engineering structures only from the response data collected in vibration tests. This
toolbox consists of three modules: the first is used to process and treat the signals
collected in the vibrations tests; the second is designed for allowing user to add the
information related to the position and orientation of the accelerometers to the data files;
the last module is used to extract the modal parameters from the response data files preprocessed
in the first two modules. In the theoretical stage, numerical models were
created to simulate de dynamical behavior of the structures under study. By comparing
the results from both stages of analysis, it is observed that the experimental and
theoretical results are in good agreement for the first modes of vibration. The
experimental results showed that the approach developed for output-only modal analysis
of civil engineering structures using stochastic state-space based methods was very
efficient for identification of the modal parameters of the analyzed structures.
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