A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Unsteady galloping of bridge decks during the launching phase ; Instationäres Galloping von Brückendecks während der Vorschubphase
The present work deals with the unsteady galloping instability, which arises at low reduced flow velocities, for steel-concrete composite bridge decks during the incremental launching phase. In this particular situation, the light weight and bluff shape of the steel box, which is normally first launched, imply a high proneness to the risk of unsteady galloping. The main goal of this thesis is to understand the unsteady galloping with respect to these special cross sections, which have not been investigated in depth before, and to develop an analytical approach for the modeling of unsteady galloping as a basis for design of bridges. Wind tunnel tests on three sectional models, among which are a generic bridge deck model with typical open cross section and two reference cylinder models, confirmed the high proneness to unsteady galloping instability for the particular situation of bridge launching. Especially, the typical unsteady galloping which arises due to the interaction with Kármán-vortex induced vibration was observed at the 4 deg mean flow incidence of the bridge deck model, fixing the galloping onset at the Kármán-vortex resonance wind speed up to a quite high Scruton number (the mass-damping parameter). In contrast, at the null mean flow incidence of the bridge deck model, the unsteady galloping was initiated in less understandable manner. Subsequently, mathematically modeling the unsteady galloping was carried out, with a modified form of Taumra’s nonlinear wake oscillator model. Satisfying predictions have been achieved not only for a 2:1 rectangular cylinder, but also for the bridge deck model at its 4 deg mean flow incidence. Attention was also paid to the so-called physical considerations in the wake oscillator model. Further modifications for the wake oscillator model were consequentially proposed, exhibiting better agreements with the physics of the near-wake of sharp-edged bluff body, maintaining at the same time a good capability for the predictions of unsteady galloping behaviors. Finally, the ...
Unsteady galloping of bridge decks during the launching phase ; Instationäres Galloping von Brückendecks während der Vorschubphase
The present work deals with the unsteady galloping instability, which arises at low reduced flow velocities, for steel-concrete composite bridge decks during the incremental launching phase. In this particular situation, the light weight and bluff shape of the steel box, which is normally first launched, imply a high proneness to the risk of unsteady galloping. The main goal of this thesis is to understand the unsteady galloping with respect to these special cross sections, which have not been investigated in depth before, and to develop an analytical approach for the modeling of unsteady galloping as a basis for design of bridges. Wind tunnel tests on three sectional models, among which are a generic bridge deck model with typical open cross section and two reference cylinder models, confirmed the high proneness to unsteady galloping instability for the particular situation of bridge launching. Especially, the typical unsteady galloping which arises due to the interaction with Kármán-vortex induced vibration was observed at the 4 deg mean flow incidence of the bridge deck model, fixing the galloping onset at the Kármán-vortex resonance wind speed up to a quite high Scruton number (the mass-damping parameter). In contrast, at the null mean flow incidence of the bridge deck model, the unsteady galloping was initiated in less understandable manner. Subsequently, mathematically modeling the unsteady galloping was carried out, with a modified form of Taumra’s nonlinear wake oscillator model. Satisfying predictions have been achieved not only for a 2:1 rectangular cylinder, but also for the bridge deck model at its 4 deg mean flow incidence. Attention was also paid to the so-called physical considerations in the wake oscillator model. Further modifications for the wake oscillator model were consequentially proposed, exhibiting better agreements with the physics of the near-wake of sharp-edged bluff body, maintaining at the same time a good capability for the predictions of unsteady galloping behaviors. Finally, the ...
Unsteady galloping of bridge decks during the launching phase ; Instationäres Galloping von Brückendecks während der Vorschubphase
Chen, Cong (author) / Thiele, Klaus / Bartoli, Gianni
2022-07-15
Theses
Electronic Resource
English
Unsteady galloping of bridge decks during the launching phase
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Unsteady galloping of bridge decks during the launching phase
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Unsteady galloping of bridge decks during the launching phase
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