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Please use this identifier to cite or link to this thesis: http://hdl.handle.net/10589/89772

Author: PAGANI, ANDREA
Supervisor: ZASSO, ALBERTO
Coordinator: COLOSIMO, BIANCA MARIA
Assistant supervisor: ARGENTINI, TOMMASO
ROCCHI, DANIELE
Department : DIPARTIMENTO DI MECCANICA
PhD course: INGEGNERIA MECCANICA
PhD course and area: Dynamics and vibration of mechanical systems and vehicles
Cycle: 26
Scientific Disciplinary Sector: ING-IND/16 TECNOLOGIE E SISTEMI DI LAVORAZIONE
Date: 28-Mar-2014
Title: Numerical and experimental analysis of uncertainties effects on non-conventional flutter instability of super-long suspended bridge
Italian abstract: Finally, even if the present work focus its attention on the flutter velocity, it is worth noting that useful information can be obtained by the analysis of the residual damping that gives information about the stability of the structure at mean wind speed whit typical of the in-service operative conditions of the bridge.
English abstract: The present work deals with the numerical and experimental analysis of uncertainties effect on flutter instability of the Izmit Bay Bridge. The innovative aspect of this research is that the uncertainties propagation analysis is referred to a bridge that presents a non-conventional flutter mechanism. It was highlighted during the wind tunnel tests performed on a 1:220 full-bridge aeroelastic model. Two vertical-torsional instabilities arise at the same mean wind speed showing, surprisingly, a not negligible contribution of vertical side-span mode. The numerical analysis of the flutter instability was able to reproduce the observed a-typical flutter that made this bridge unique by a wind engineering point of view. In fact, the classical flutter mechanism is not able to reproduce the experimentally observed phenomenon because it involves more than two modes characterised, on one hand, by high torsional/vertical frequency ratio and, on the other hand, modes with frequencies closer to the homologous torsional ones but not identical mode shapes. A preliminary research to assess a quantitative evaluation of both structural and aerodynamic parameters was performed. On one hand, by a structural point of view, a greater uncertainty relays on the effectiveness of the FE model of the bridge. On the other hand, facing with aerodynamic coefficients, they can be potentially modulated by a lot of parameters and in particular their consistency with the ones of the real structure (not yet built). An attempt to evaluate the sensitivity of the deck section to a change in the fluid structure interaction was performed increasing and decreasing its bluffness. The robustness of the aerodynamic coefficients was also tested, evaluating if a slightly change of the angle of attack can leads to very different results dealing with the stability analysis. The measurements process error was also associated to them and, it was found to be a (polynomial) function of the reduced velocity. The above mentioned uncertainties were adopted to perform a reliability analysis. The simulations highlight that uncertainty of structural parameters have greater effects than the one of the aerodynamic coefficients, even if of the same order of magnitude. The measurement errors can be disregarded without a great lost in accuracy. Combining both the source of uncertainties, the synchronous flutter velocities of the two presented kind of flutter is a circumstance that is typical of the nominal case but, by a statistically point of view, it occurs only in the 20% of the simulations. The main mechanism of instability is the one caused by the coupling of the modes with an anti-node at mid-span. Finally, this analysis highlight that, under specific conditions, the system shows instability at relative low mean wind speed due to a modification in the flutter mechanism that depends on the particular S-shape behaviour of the damping of the first torsional mode (due to both structural and aerodynamic uncertainties). Finally, even if the present work focus its attention on the flutter velocity, it is worth noting that useful information can be obtained by the analysis of the residual damping that gives information about the stability of the structure at mean wind speed whit typical of the in-service operative conditions of the bridge.
Italian keywords: affidabilità; ponti sospesi a lunga campata; metodo Monte Carlo; incertezza; aeroelasticità; instabilità da flutter; smorzamento residuo; ponte di Izmit
English keywords: reliability; long span suspension bridge; Monte Carlo simulations; uncertainties; aeroelasticity; flutter instability; residual damping; Izmit bay bridge
Language: eng
Publisher: Politecnico di Milano
Type of document: Tesi di dottorato
Appears in Collections:POLITesi >Tesi di Dottorato

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