Brief Analysis of Natural Frequency and Its Corresponding Influences for Old Tacoma Narrows Bridge Using Finite Element Method

Abstract

AbstractThe failure of the 1940 Tacoma Narrow Bridge has become a famous case for the bridge engineering study and structural dynamics courses nowadays. The collapse of the old Tacoma Narrow Bridge was owing to the torsional oscillation caused by the wind at the velocity of 67 km/h, as a resonance occurred when the torsional oscillation met the natural frequency of 1940 Tacoma Narrow Bridge. Therefore, detailed determination of the natural vibration frequency of the old Tacoma Narrow Bridge by applying FEM using will be discussed in this report. For the methodology of research project, the structural behaviour of Tacoma Narrow Bridge is detailed analysed. A model with a scale of 1:1 to the actual bridge is established via ANSYS and its structural behaviour is only focusing on the vibration mode, which will be done by program controlling in modal analysis. By determining the natural frequency of the bridge, the stiffness (k) is directly related to the natural vibration frequency while the mass is inversely relevant to the natural vibration frequency. These features can be manipulated to avoid the phenomenon of resonance and hence prevent the possibility of collapse. Moreover, the aerodynamic structure of the suspended bridges can be developed to avert the resonance caused by torsional flutter. Therefore, this research can assist engineers to address relevant issues and be a simple guideline when designing a suspension bridge.KeywordsTacoma narrow bridgeTorsional oscillationNatural frequencyFinite element methodANSYS modelling