The Dynamic Characteristics of Railway Portal Frame Bridges: A Comparison between Measurements and Calculations

Railway bridges are subjected to significant dynamic loads. A numerical model of the bridge structure that captures its dynamic characteristics as accurately as possible is essential for the simulation of train crossings. However, most existing Calculation Models either do not consider the dynamic interaction between the structure and the soil, known as the soil-structure interaction (SSI), or give it only secondary importance. As a result, the accuracy of the predicted dynamic characteristics is affected. This paper illustrates how the dynamic interactions of abutments impact the portal frame bridge's SSI. This influence prompts the question of incorporating the frequency-dependent influence of the structure-soil-structure interaction (SSSI) into the modelling process. We propose a conservative estimation of the frequency range influenced by the shear wave interference of the SSSI and recommend using it as an application limit in the development of computational models. Based on this estimation, a Calculation Model is presented. In this approach, the SSI is considered using the well-known quasi-static spring-damper method from foundation vibration analysis, adhering to limitations based on the SSSI. For the application of the presented Calculation Model, four concrete portal frame bridges with spans between 9 m and 17 m along the high-speed line from Nuremberg to Munich, Germany, are investigated by analyzing the dynamic characteristics and comparing them with the prediction of the proposed numerical Calculation Model. The presented method shows good calculation accuracy.