Natural Oscillations of Suspension Bridges

by Frank Van der Woude, (M.ASCE), Sr. Lect. in Civ. Mech. Engrg.; Univ. of Tasmania, Hobart, Australia,

Serial Information: Journal of the Structural Division, 1982, Vol. 108, Issue 8, Pg. 1815-1830

Document Type: Journal Paper


Natural modes and frequencies of a simple span suspension bridge with straight backstays are investigated, theoretically and experimentally. Fourier series representations of cable displacements are used in conjunction with the Lagrange method to represent the system with a small number of degrees-of-freedom. Bridge system matrices are derived which take account of cable, gravity, bending, and torsional stiffnesses. Natural modes and frequencies are obtained as the eigensolutions of small order system matrices. A numerical example is given from which approximate frequency formulas are derived. Experimental results in the form of frequency response curves, are presented for a laboratory model. Agreement between theory and test is within 5 percent or better.

Subject Headings: Cables | Suspension bridges | Oscillations | Natural frequency | Cable stayed bridges | Matrix (mathematics) | Span bridges | Fourier analysis

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