PRACTICAL EVALUATION METHOD FOR FUNDAMENTAL NATURAL FREQUENCIES OF TWO-GIRDER BRIDGES BASED ON BEAM THEORY

Abstract

Two-girder bridges are prone to oscillation due to wind such as the torsional vortex excitation. In order to estimate a wind speed of the excitation, it will be necessary to evaluate the fundamental vertical and torsional natural frequencies at an initial stage of bridge design. According to the conventional beam theory, this paper provides a practical method to evaluate the fundamental natural frequencies of these bridge structures. Effectiveness of the proposed method is discussed for existing highway bridges of two-girder type compared with the evaluated and computed natural frequencies. These results showed that the present method could estimate the fundamental vertical and torsional natural frequencies with sufficient accuracy and less complexity.