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29. janúar 2015 - 11:40
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Stofa 157

Sigurbjörn Bárðarson flytur fyrirlestur um verkefni sitt til meistaraprófs í byggingarverkfræði. Verkefnið ber heitið Modal identification of non-classically damped structures.
Ágrip
This thesis focuses on modal identification of structural systems. System Identification can be used to create mathematical models of structures which can then be used in simulation and design. Modal identification provides a valuable means of calibrating, validating, and updating finite element models of structures. This thesis reviews the standard techniques of system identification. Basic theoretical background of the different methods of practical use is presented. Demonstrations of the described methods are provided by using response simulated from known systems which are then used in system identification. Starting with single degrees of freedom systems, basic theory in relation to dynamics and modal analysis of multi degree of freedom systems are presented with examples used in the identification procedure, along with methods for non-classically damped systems. As a case study, system identification of a base-isolated bridge is undertaken. Modal properties of the bridge are computed from a finite element model. A simulated response is used in system identification to check whether the identified modal properties match that of the finite element model. One of the issues investigated is the effect of damping provided by the rubber bearings of the base isolation system. This damping makes the system non-classically damped. The results indicate that system identification for a structure like this is feasible and reliable estimates of vibration periods and damping ratios are obtained. It was also observed that increase in damping ratio in the rubber bearings results in modal damping ratios that are different than the commonly used Rayleigh damping model.
Leiðbeinandi: Rajesh Rupakhety, dósent við Umhverfis- og byggingarverkfræðideild HÍ og Ragnar Sigbjörnsson, prófessor við Department of Structural Engineering, NTNU, Noregi.
Prófdómari: Karim Afifchaouch, lektor við Polytechnique School of Architecture and Urbanism EPAU, Alsír.
Ágrip
This thesis focuses on modal identification of structural systems. System Identification can be used to create mathematical models of structures which can then be used in simulation and design. Modal identification provides a valuable means of calibrating, validating, and updating finite element models of structures. This thesis reviews the standard techniques of system identification. Basic theoretical background of the different methods of practical use is presented. Demonstrations of the described methods are provided by using response simulated from known systems which are then used in system identification. Starting with single degrees of freedom systems, basic theory in relation to dynamics and modal analysis of multi degree of freedom systems are presented with examples used in the identification procedure, along with methods for non-classically damped systems. As a case study, system identification of a base-isolated bridge is undertaken. Modal properties of the bridge are computed from a finite element model. A simulated response is used in system identification to check whether the identified modal properties match that of the finite element model. One of the issues investigated is the effect of damping provided by the rubber bearings of the base isolation system. This damping makes the system non-classically damped. The results indicate that system identification for a structure like this is feasible and reliable estimates of vibration periods and damping ratios are obtained. It was also observed that increase in damping ratio in the rubber bearings results in modal damping ratios that are different than the commonly used Rayleigh damping model.
Leiðbeinandi: Rajesh Rupakhety, dósent við Umhverfis- og byggingarverkfræðideild HÍ og Ragnar Sigbjörnsson, prófessor við Department of Structural Engineering, NTNU, Noregi.
Prófdómari: Karim Afifchaouch, lektor við Polytechnique School of Architecture and Urbanism EPAU, Alsír.