Keywords: rail bridge interaction, bridge expansion, geodetic surveying, bridge monitoring, expansion joints, continuous welded rail.

This paper is focused on monitoring the interaction between rails and bridges characterized by a large expansion length. The bridge is situated close to the Czech-Austria state border in the international rail line. The assumptions and values used for the static parameter analysis were required to evaluate by data of real bridge and rail performance.

Monitoring of the Znojmo viaduct includes a continual measurement of the ballast pressure on the bridge trough divider at the end of the bridge with movable bearers, strain in the structure of this bridge ballast trough divider, thermal expansion of the bridge steel structure relatively to abutments wall, shift of rails relatively to the bridge structure, the strain in rails on the bridge, temperature of the bridge structure, rails and air. Monitoring also includes a survey of the longitudinal displacements of the track length on the bridge and its vicinity by terrestrial and satellite geodetic methods. Investigations also include a measurement of expansion joints settings. The monitoring lasted two years from September of 2009 to September of 2011.

The longitudinal displacements which were investigated by the continual monitoring and geodetic surveying provide data about real bridge-rail interaction arising from temperature influences. The basic qualitative conclusion is that the track on the bridge does not respond to the continuous welded rail behaviour. The track generally follows the bridge expansion. The equivalent coefficient of thermal expansion was evaluated using the value of 9.7x10^-6 K^-1 which is significantly lower than the value of thermal expansion coefficient for steel as structural material.

The disproportion between rail and bridge temperatures in daily cycles and the different thermal expansion behaviour causes longitudinal forces in the track. These forces are transferred to the closing trough divider. So the ballast pressure and consequently the stresses in the divider are subjected to the daily temperature cycles. The extreme values of pressure in the ballast are caused by impact load during train passage. The impact loads probably originate from flat wheels. The extreme pressure values, which are in a range 300-500 kPa, lead to the deterioration of the ballast. A reconsolidation of the ballast during seasons and especially impact loads can result in undesirable settlement of the track at the end of the bridge and consequently to track quality deterioration.

Future analyses should be focused on a comparison between the experience which is included in the regulations of the Czech Railway Infrastructure Administration and new calculation results.

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