Dynamic response of two-span continuous composite bridges

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Abstract
With the continuing trend towards lighter and more flexible continuous composite bridges, problems of vibration are becoming increasingly more important. Furthermore, fatigue cracking can be a real problem in such bridges when subjected to several thousands of resonance cycles over its life. In this paper the dynamic response of continuous composite bridges and the influence of repeated loading at resonance frequency on the structural response are investigated. A closed-form series solution based on orthotropic plate theory is developed to predict the natural frequencies of two-span continuous composite bridges. Expressions for the equivalent rigidities of a composite bridge are also given. The results are verified and substantiated by experimental results from 1/4-scale bridge model. Estimates of frequencies based on beam theory as well as the effects of concrete and fatigue cracking on the natural frequencies and strain range are examined. Finally, it is shown that a fatigue-cracked composite bridge, when properly repaired, can regain most of its stiffness and ultimate load-carrying capacity. Key words: bridges, composite, concrete, continuous, dynamics, fatigue, orthotropic, rigidities, steel, tests.

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