A Rapid Algorithm of Fundamental Frequency for the Freestanding Pylon of Suspension Bridges

Abstract

The combination of Rayleigh’s energy method and Southwell’s frequency composition method denoted the fundamental vibration frequencies of the freestanding pylon of suspension bridges as the composition of several subsystem frequencies. The subsystems consisted of deformation and inertia components. Thus, the algorithm for calculating the fundamental vibration frequency of the freestanding pylon of suspension bridges was derived through the rational selection of the deflection function. Take the middle steel pylon of Taizhou Bridge as a calculation example. The impact of top additional mass ratio, structure shear deformation, and vibration of the bearing platform on fundamental vibration frequency was analyzed. The numerical calculation and real bridge field vibration test show that (1) the fundamental vibration frequency of the pylon decreases as top additional mass ratio increases, and (2) the vibration of the bearing platform should not be ignored even if ignoring shear deformation only has a slight impact on the calculation results. The algorithm is not only suitable for pylons with a fixed base or additional mass at the top but also for other high buildings, chimneys, and structures with complicated sections.