Numerical evaluation of the mid-span assumption in the calculation of total load effects in railway bridges

• Maximum load effect not necessarily at mid-span.
• Emphasis on resonant situations in railway bridges.
• Mid-span assumption might lead to significant errors particularly for bridge deck accelerations.
• Discussion on reasons for adverse situations.
• Numerical model includes vehicle–track–bridge interaction.

Maximum load effects in simply supported railway bridges traversed by trains are generally investigated at the mid-span section. However, this assumption is not necessarily correct. The true maximum load effect might occur at some other bridge section and its magnitude could be significantly greater. This paper quantifies the underestimation of the load effects as a result of exclusively considering the middle section, with special emphasis on resonant situations. A 2D numerical model of a vehicle–track–bridge system was used to evaluate different vehicle velocities, bridge properties and track irregularity conditions. The error due to the mid-span assumption depends on the particular case considered but can be related to the relative energy content of the higher modes of vibration. The results show that the error is greatest for accelerations, smaller for bending moments and is almost negligible for displacements.