Flutter instability of long-span suspension bridges: The case-study of the 1915Çanakkale Bridge in Turkey

The Dardanelles region have always been considered an important cultural and economic hub first of the Ottoman Empire and then of modern Turkey. The construction of a long-span suspension bridge over the Dardanelles Strait was always considered an important goal for the Turkish government and was completed in 2022, setting the current record for the longest span in the world. The construction of the 1915Çanakkale Bridge has always been regarded as a complex structural engineering project. Through the cooperation of the various research and studies, particularly Danish and Chinese, many difficult environmental conditions have been faced and solved. The collapse of the Tacoma Narrows Bridge in 1940 pushed research and design towards understanding the critical aerodynamic phenomena resulting from wind-structure interaction. By employing numerical and analytical methods and using software like ANSYS and MATLAB, this thesis develops flutter instability analysis with the goal of understanding how the 1915Çanakkale Bridge reacts to dynamic wind phenomena. The introductory section includes a brief historical overview from the ancient suspension bridges to the development in the early 1960s of long-span suspension bridges with aerodynamic decks. The flutter treatment using analytical and numerical methods is then presented and it is described mathematically in terms of one and more DOF analysis. In addition, Namini and Albrecht analysis is suggested. The design and realization of the 1915Çanakkale Bridge is then presented with the innovative aspects of foundations and deck construction, and wind analysis up to the monitoring system, the most modern in the world. As a major project, it involved many researchers in advanced studies of the overall behavior of the bridge using wind tunnels on scale models; two of these are reported with their data and results. The study focuses on the main span deck, and the models, a fish-bone and a two-axis deck models, are presented in the following chapters. Then a zero-wind modal analysis is performed to estimate natural frequencies and modes of vibration by recursively correcting stiffness properties. The introduction of flutter derivatives into ANSYS software allows the specific analysis with the aim of determining the critical frequency and velocity of the wind, which initiates the instability. For wind speed and critical flutter frequency, the results of analysis with MATLAB and ANSYS software are in accordance with an error of less than 1%. In addition, the results obtained correlate strongly with the literature values from authoritative studies conducted in Denmark and China. Subsequently, the single-mode criterion, a simplified one-DOF flutter analysis criterion to study the problem in uncoupled form, is introduced. The implementation of Albrecht's method enabled to understand the specific nature of the bridge deck. The aerofoil twin-box section's shape, which is like an aircraft wing, gives the structure an exceptional level of stability against one-DOF flutter. In conclusion, it has been found that the numerical and analytical methods used confirm the efficient behavior of the 1915Çanakkale Bridge towards the critical flutter phenomenon. The perfect combination of design and construction of this important structure laid the foundation for subsequent innovation and research in the field of long-span suspension bridges.