Αναγνώριση ιδιομορφικών χαρακτηριστικών κατασκεύων βάσει μετρήσεων των ταλαντώσεων σε περιβαλλοντικές και σεισμικές διεγέρσεις : θεωρία, λογισμικό και εφαρμογές
Experimental modal analysis using ambient and earthquake vibrations : theory, software and applications
Autor
Ντότσιος, ΕυάγγελοςSupervisor name
Παπαδημητρίου, Κωνσταντίνος
Fecha
2009Language
en
Access
free
Resumen
This thesis addresses the problem of identifying the modal properties of structures using vibration
measurements. Modal identification methodologies are proposed based on vibration
measurements induced by artificial, ambient or earthquake loads applied on the structure. A
modal model of the structure is identified using a weighted least-squares approach and measured
time histories at selected locations of a structure. For artificially induced and ambient vibration
measurements, the identification is performed in the frequency domain using respectively
frequency response functions and cross power spectral densities. For earthquake induced
vibrations, the identification is performed in both time and frequency domains. The modal
identification methods presented in this work treat generalized non-classically damped modal
models.
The identification of the modal parameter (modal frequencies, modal damping ratios, modeshape
components and modal participation factors) is accomplished by introducing a computationally
very efficient three step approach as follows. In the first step, stabilization diagrams are
constructed containing frequency and damping information. The modeshape components and
participation factors are estimated in a second least-squares step, based on the user selection of
the stabilized poles. The first two steps involve non-iterative procedures and result in solving
linear algebraic systems of equations. 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 is introduced to solve a fully nonlinear optimization problem using available iterative
gradient-based optimization algorithms. In this thesis, theoretical developments as well as
software implementation issues are presented.
The methodologies and software developed are applied for the identification of the modal
characteristics of a small laboratory structure for the case of artificial induced vibration
measurements, as well as the identification of the modal characteristics of three bridges, the
under construction R/C bridge of Egnatia Odos located at Metsovo (Greece), and two other
representative R/C bridges of Egnatia Odos located at Polymylos and Kavala (Greece) for the
cases of ambient and earthquake induced vibration measurements. Results provide qualitative
and quantitative information on the dynamic behaviour of the systems and their components
under different types of excitations.
All modal identification methodologies presented in this work are implemented in user-friendly
software, termed Modal Identification Tool (MITooL). The software which includes graphical user
interface allows the full exploration and analysis of signals that are measured on a structure when
it is excited by artificial, ambient or earthquake loads. A user manual is also presented which
gives details for the operations and prospects of the MITooL software. Step-by-step examples of
modal identification are presented to demonstrate the applicability of the software.
Academic publisher
Πανεπιστήμιο Θεσσαλίας. Πολυτεχνική Σχολή. Τμήμα Μηχανολόγων Μηχανικών.