1. Introduction
With the recent development of high-speed trains globally, structural interaction plays an important role in estimating the impact of rail on the bridge and the optimum design of the bridge system for the safe passage of trains without disturbing the passengers' riding comfort. The UIC 774-3, Eurocode in 1991-2, RDSO, Korean code, ACI, and various codes and standards provide methodologies for considering rail-bridge interaction problems in the design and analysis of railway bridges. These guidelines take into account the dynamic interactions between trains and bridges, which can affect the stress, displacement, and stability of the rail during train passage. Based on experimental and numerical studies, these guidelines provide limiting values for stress, displacement, and stability of the rail to ensure railway bridges' safe and reliable performance. These limiting values are derived to prevent excessive deformations and stress in the rail that could lead to failure of the rail or other bridge components.
1.1 What is Rail-Structure Interaction
Rail Structure Interaction (RSI) is a complex phenomenon that occurs between the rail and the structure when Continuous Welded Rail (CWR) is used on a railway bridge. Unlike conventional rails, CWRs are continuous rails, so each displacement that occurs on bridges and rails is influenced by each other due to train loading (vertical and longitudinal direction) and temperature changes. Due to the following effects, safety problems such as buckling or fracture may occur on the rail during use. Therefore, when using CWR, it is necessary to review regardless of the type of train or track (ballast track, concrete slab track). Many parameters affect the rail-structure interaction. In most cases, the effects due to changes in temperature, acceleration/braking, and bending due to vertical loading play an important role.
1.1.1 Actions due to changes in temperature
The variation of temperature in long welded rail will cause expansion and contraction of
rail but the rail is connected to the sleeper using an elastic fastener which will prevent any
relative movement between the rail and the sleeper, which leads to the accumulation of axial force in the rail.
As per UIC 774-3, the following temperature load should be considered for the RSI.
- Rail = ± 50 °C
- Bridge = ± 35 °C
Figure 1.1 Axial force in the continuous welded rail
1.1.2 Actions due to braking and acceleration
As the vehicle travels along the rail depending upon the type of vehicle, longitudinal load, and direction of travel due to acceleration and braking of the vehicle it will try to move the rail in the direction of movement. Longitudinal resisting forces are generated by the longitudinal displacement of the rail due to braking and acceleration forces.
As per UIC 774-3, the following braking/acceleration load should be considered for the RSI.
- Acceleration: qlak= 33 kN/m per track, with L x qlak ≤ 1000 kN
- Braking: qlbk= 20 kN/m per track, with L x qlbk ≤ 6000 kN
Figure 1.2 Braking and acceleration forces action on the bridge
1.1.3 Actions due to bending of deck
Vertical train loads cause bending of the superstructure and cause end rotation between the upper edge of the deck end or between the upper-end surface of the continuous deck as shown in the figure below.
In addition, due to the rotation angle generated by bending, displacements are also transmitted to the rails, generating additional stresses. The conceptual diagram of the horizontal displacements due to the bending of the superstructure is as follows.
Figure 1.4 Effect of deck bending (UIC 774-3)
Vertical train loads should be loaded at the most unfavorable position to find the most critical effect.
You can check more of these details in the download file.
1.1.3 Actions due to bending of deck
1.2 RSI using a computer program
1.2.1 Simplified separate analysis model
1.2.2 Complete analysis model
2. Test case as per UIC 774-3 - A1-3
2.1 Section Properties
2.2 Modelling in MIDAS CIVIL
2.3 Results from Separate Analysis Model
2.4 Results from the Complete Analysis Model
2.5 Summary
3. Conclusion
Author
