published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

The failure of the Tacoma Narrows Bridge in November 1940 was a major course of the beginning of research on the Aerodynamic Stability of Suspension Bridges. Wind has wrecked suspension bridges for over a century but the underlying cause, an increasing harmonic amplitude due to wind, has been ignored until recently. For many years bridges have been designed to withstand horizontal wind pressure, but the lift force and the overturning moment due to wind have been overlooked. This investigation, in part, was conducted so that aerodynamic coefficients of certain bridge sections not heretofore investigated could be determined. With data from these tests engineers can determine beforehand whether the sections, if used, will be safe against uplifting, sliding, overturning, and of building up oscillations of catastrophic proportions. The second part of this thesis is devoted to the determination of the torsional oscillation effects in order to predict the dynamic wind characteristics of bridge sections. The dynamic tests are necessary to verify the analytical predictions obtained from the static tests and are valuable in obtaining the aerodynamic constants necessary for the complete solution of the bridge analysis. / Master of Science

The aerodynamic characteristics of bridge sections can be determined by simple wind-tunnel tests. These characteristics can then be used to determine the lift force and overturning moment on any bridge section without large scale model tests. Also, the slope of the lift and torque curves obtained in these tests determine the aerodynamic stability or instability of the bridge section. Our problem was to determine the aerodynamic characteristics of typical bridge sections and attempt to find aerodynamically stable sections. The lift, torque and drag curves were obtained by holding the model stationary at different angles of attack in the wind-tunnel. The results obtained from these tests were confirmed by pressure distribution tests. In these tests the model was held stationary in the air stream, while pressure was measured by manometer readings at eleven points across the desk. Results of this investigation show that girder sections with deck at mid-height or flush are unstable except for low d/b ratios. Sections that yield both torsional and vertical stability are truss sections, an H-section with center slot and fins, and an H-section with fins. Other modifications of sections furnish curves which indicate neutrality. These sections can be used then sufficient damping is present. This investigation also shows that present wind-load specifications are inadequate and need to be revised. / Master of Science

The purpose of this investigation was to observe the action of the various models oscillating torsionally in a fluid stream of uniform velocity. From static tests and pressure distribution examinations predictions of vertical and torsional stability trends have been made and approximate aerodynamic constants evaluated. Observations of the change in energy required to maintain uniform oscillations will indicate the stability of the models and facilitate a more accurate evaluation of the aerodynamic constants. A secondary purpose of the investigation was to verify the predictions made regarding stability based on the static force measurements previously obtained. / M.S.

This research is aimed at investigating and analyzing the rain-windinduced cable vibration phenomena experienced in cables of cable-stayed bridges and also the countermeasures employed by engineers to mitigate the large-amplitude vibration problem reported by various researchers around the world. In order to investigate the problem of the water rivulet creation at the top of the cable surface, a single-degree-of-freedom (SDOF) analytical model was developed and analyzed. This thesis studies the aerodynamic instability of cables in cable-stayed bridges by doing literature review of a typical in-situ test, developing a single degree-of-freedom (SDOF) analytical model, and an ANSYS finite element model. Furthermore, a linear viscous damper that acts as a countermeasure to the large amplitudes of vibration is reported and analyzed. The suppression characteristics and damper effectiveness of such countermeasure are summarized. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection