Horizontally curved bridges are used in the development of highways and interchange facilities. In today’s roadway system, they are growing more popular. The benefit of utilizing curved girders is that the result in longer spans and fewer piers in curved bridges. Because of its curvature, the behavior of a curved I-girder bridge differs from that of a straight I-girder bridge. The dynamic properties of curved girder bridge are more complicated and less understandable topic, this is because the curvature might result in a geometrically unstable condition. Because of the non-uniform torsion caused by the curvature, the structural behavior of horizontally curved I-girders is significantly different from that of straight I-girders. Therefore, the dynamic properties of these horizontally curved bridges with curved I-girders must be more clearly identified and explained. Free vibration analysis is one of the most significant elements in any dynamic analysis process since it is independent of any form of loading. It is a common initial step in completing a dynamic analysis to determine the structure’s natural frequencies and mode shapes without considering damping. In this study, the natural frequencies and related mode shapes of a bridge superstructure are investigated. The study has been carried out on a straight bridge and curved bridge models of varying radius of curvature in order to identify their natural frequency and associated mode shapes while keeping the cross section of the bridge and span length same for each model. The straight and curved I-girder bridges have been analyzed using Finite ElementMethod analysis and the behaviors of those bridge models are compared with each other. The results show that as the radius of curvature decreases,the vertical mode frequency decreases with itwhile the torsional mode frequency increases. Again with a decrease in the curvature radius, the difference becomes greater between inner and outer girder displacement. As a result of the influence of torsional frequencies on horizontally curved models, the bridge can easily vibrate under external dynamic load, compromising its stability.

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