Ανάπτυξη μεθόδων αναγνώρισης ιδιομορφικών χαρακτηριστικών κατασκευών υπό σεισμικά φορτία

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.