Ανάπτυξη μεθόδων αναγνώρισης ιδιομορφικών χαρακτηριστικών κατασκευών υπό σεισμικά φορτία
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Author
Νικολάου, ΙωάννηςSupervisor name
Παπαδημητρίου, Κωνσταντίνος
Date
2008Language
el
Access
free
Abstract
The problem of identification of the modal parameters of a structural model using earthquakeinduced
vibration measurements is addressed. It is based on a weighted least-squares approach
using multiple-input multiple-output measured time histories at the base supports and at selected
locations of a structure. The identification is performed in the time domain and in the frequency
domain. Existing modal identification methods have been extended in this work to treat
generalized non-classically damped modal models. The case of classically damped modal
models is treated as a special case.
The identification of the modal parameters (modal frequencies, modal damping ratios,
modeshape components and participation factors) is accomplished by introducing a three step
approach: in the first step, a stabilization diagram is constructed containing frequency and
damping information. Next, the modeshape components and participation factors are found in a
second least-squares step, based on the user selection of the stabilized poles. Finally, in order to
improve the estimation of the modal characteristics especially for the challenging case of closely
spaced and overlapping modes, a third step concerning the fully nonlinear optimization problem is
addressed. Computational issues involving the solution of the optimization problems and the
evaluation of analytical expressions of the gradients of the objective functions are also discussed.
The validation of the proposed methodologies and algorithms is presented using simulated
data from a 3 DOF and a 10 DOF spring mass chain model. The methodologies are next applied
for the identification of the modal characteristics of two bridges, the R/C bridge of Egnatia Odos
located at Polymylos, Greece, and the Vincent Thomas cable suspension bridge located at Los
Angeles, USA. Results provide qualitative and quantitative information on the dynamic behaviour
of the bridge systems and their components under earthquake-induced vibrations.
Academic publisher
Πανεπιστήμιο Θεσσαλίας. Πολυτεχνική Σχολή. Τμήμα Μηχανολόγων Μηχανικών Βιομηχανίας.