Dynamics of thick bridge beams and its influence on fatigue life predictions

• An analytical model for moving load analysis of thick beams is derived.
• The model is used for dynamic analyses of typical bridge beams.
• The influence between dynamic properties and accumulated fatigue damage is examined.
• A new reduced dynamic amplification factor for fatigue assessment is suggested.

An analytical model for moving load analysis is derived based on the Timoshenko beam theory. The model enables rapid and reliable analyses of the influence of dynamics on the fatigue life prediction of thick beams. This type of beams is typical for open deck railway bridges. The number of modes required in a modal superpositioning is studied as well as the influence of damping and support stiffness. A total of 22 bridge beams from open deck bridges presented in the literature is included in the study. The results clearly show a fundamental difference in the behaviour of one span beams and continuous beams. Especially in the case of assessment of existing bridges, the quasi static model of the Eurocode renders an excessive safety margin. For the majority of continuous beams studied, the dynamic response is lower than the static response resulting in no dynamic amplification. Such an outcome can have a substantial influence on the remaining fatigue life prediction due to the exponential relation between the stress range and the fatigue life.