Free Torsional Vibrations of Suspension Bridges

by Ahmed M. Abdel-Ghaffar, (A.M.ASCE), Asst. Prof.; Dept. of Materials Engrg., Univ. of Illinois at Chicago Circle, Chicago, Ill.; formerly, Research Fellow, Civ. Engrg. Dept., California Inst. of Tech., Pasadena, Calif.,

Serial Information: Journal of the Structural Division, 1979, Vol. 105, Issue 4, Pg. 767-788

Document Type: Journal Paper


A generalized theory of free torsional vibration for a wide class of suspension bridges with double lateral systems is developed, taking into account warping of the bridge deck cross section and the effect of torsional rigidity of the towers. The analysis is based on a linearized theory and on the use of the digital computer. A finite element approach is used to determine vibrational properties in torsion. Simplifying assumptions are made, and Hamilton's principle is used to derive the matrix equations of motion. The method is illustrated by numerical examples. The objective of the study is to clarify the torsional behavior of suspension bridges and to develop a method of determining a sufficient number of natural frequencies and mode shapes to enable an accurate practical analysis.

Subject Headings: Suspension bridges | Bridge decks | Torsion | Vibration | Bridge towers | Equations of motion | Bridge tests | Warpage

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