Determination of the optimal span length for a railway bridge crossed by various types of high-speed trains

This paper proposes a method that can be used during the preliminary design stage to determine the optimal span length of a railway bridge that minimizes its dynamic responses to the passage of high-speed trains. Since the designed speed for passage over a railway bridge is generally higher than the speed at which the resonance phenomenon occurs, the peak dynamic responses of the bridge are likely to occur when a train travels across a bridge. Therefore, this study suggests inertia and elastic spectra that represent the inertial force and elastic force per unit length of the bridge at the resonance condition, respectively. These spectra are defined as functions of the span length of the bridge, for which the type of train and damping ratio are fixed, and based on the relationship between the dynamic responses of two different railway bridges that was used as theoretical basis for the design diagram proposed by the European Rail Research Institute. The optimal span length of the bridge that produces the smallest responses is determined using the suggested spectra by quantitatively comparing the responses at resonance under various train loads as a function of the span length of the bridge. The proposed method is validated using numerical examples that consider the computation of the optimal span length of a simply supported single-span bridge crossed by individual KTX, HEMU and ICE 2 trains and combinations of these trains.