Effect of Hanger Flexibility on Dynamic Response of Suspension Bridges

• Published in: Journal of engineering mechanics 2010-12, Vol.136 (12), p.1444-1459
• Main Authors: Turmo, José, Luco, J. Enrique
• Format: Article
• Language: English
• Subjects: Applied sciences; Bridges; Buildings. Public works; Elastic beams; Exact sciences and technology; Flexibility; Free vibration; Fundamental areas of phenomenology (including applications); Girders; Hangers; Mathematical models; Physics; Solid mechanics; Structural and continuum mechanics; Suspension bridges; Suspension bridges. Stayed girder bridges. Bascule bridges. Swing bridges; TECHNICAL PAPERS; Vibration; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...)
• ISSN: 0733-9399; 1943-7889
• DOI: 10.1061/(ASCE)EM.1943-7889.0000185

Linearized continuum models of a suspended span with unloaded backstays and of a symmetric three-span suspension bridge are used to study the effects of the flexibility of the hangers on the vertical vibrations of suspension bridges. The models include elastic parabolic cables, flexible distributed hangers with variable length, and a stiffening girder represented by an elastic beam. It is shown that the free vibrations of a suspended span with unloaded backstays are controlled by five dimensionless parameters, while six dimensionless parameters control the response of a symmetric three-span suspension bridge. The results indicate that the flexibility of the hangers has a significant effect on the natural frequencies of the higher modes only when the relative stiffness of the girder is very high. The effects of hanger flexibility on the response of a suspension bridge to localized impulsive loads are also found to be small. These findings confirm the traditional, albeit previously untested, assumption of inextensible hangers. Finally, the threshold amplitudes of free vibrations that would result in the incipient slackening of the hangers are determined.