Experimental characterization of the aeroelastic response of a cable-stayed hinged-deck bridge
- Autores: Mª Elena López Núñez
- Directores de la Tesis: Sebastián Franchini Longhi (dir. tes.), Mikel Ogueta Gutiérrez (dir. tes.)
- Lectura: En la Universidad Politécnica de Madrid ( España ) en 2021
- Idioma: español
- Materias:
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- Resumen
The action of wind on civil structures and mainly the aeroelastic phenomena of bridges have been a subject of study for many researchers all around the world. The increasing slenderness and lightness of some civil structures, such as high-beam bridges or skyscrapers, has made the effects of wind on them a relevant factor, to the point of causing their collapse as happened in the well-known episode of the Tacoma bridge over the Narrows River in 1940.
There are several works aiming to understand better all the effects of the wind over bridges. However, there are still many open questions that needs to be investigated. Classically, aerolastic wind tunnel tests are performed considering 2D sectional aerodynamic models with only two degrees of freedom (DOF): vertical translation motion, and rotation motion around the centre of the mass.
The objective of the present work is focused on the aeroelastic stability analysis of the Rande Bridge. Due to the increasing amount of vehicles, and aiming to increase the bridge capacity, an expansion of the bridge was proposed. The enlargement, inaugurated in 2017, consisted in the addition of two lateral extension decks to the existing central deck. This represents a new challenging configuration from the aeroelastic stability point of view, as it introduces new degrees of freedom to be considered in the system.
A FEM model of the Cable-Stayed Hinged-Deck Bridge was used to obtain the dynamic characteristics of the real bridge (natural frequencies and normal modes). However, the FEM model is too large to be useful for the sectional test design, as it requires large computational resources and it is too complex to be implemented in the tests. To overcome this issue, a reduced 6 DOF analytical model to reproduce the main characteristics of the system is developed and tuned with the FEM results. The first 4 degrees of freedom determine the position the central and the two lateral decks, while 2 additional degrees of freedom were needed to consider the effect of the pylons. This analytical model is used to design the experimental model to be tested in the wind tunnel.
Three different test campaigns are performed with three different objectives: 1) the effect of the windward extension deck angle of attack in a model with no wind barriers; 2) the effect of different wind barriers is assessed, and 3) the effect of the windward angle of attack in a bridge with nominal wind barriers. The results shown the importance of both the angle of attack and the wind barriers in the stability characteristics of the bridge and the importance of understanding this effects to control the instabilities.
The manuscript is divided in 7 chapters. In the first chapter an introduction to fluid-structure phenomena in bridges is presented, and the objectives and methodology of the thesis are described. The dynamic characteristics of the bridge obtained with the FEM model are described on Chapter 2. In this Chapter, the analytical model is presented and tuned to match the FEM results. In Chapter 3 the development process of the experimental model is described, and the test procedure and instrumentation used in the wind tunnel facility are presented. Then in the three following chapters, the main results of the three experimental campaigns are presented: the effect of the angle of attack in the windward extension deck in a model with no wind barriers is assessed in Chapter 4; Chapter 5 is devoted to study the effect of different wind barriers, and the combination of both effects by using a model with nominal barriers is analyzed in Chapter 6. Finally, in Chapter 7 the main conclusions of the thesis are drawn, and future work to improve the current knowledge on bridge stability is proposed.
