Study and Comparison Different Methods of Stiffness Transition In Railway Short Span Bridge Transition Zone

Abrupt and non-uniform changes in track vertical stiffness in railway bridges transition zone, increase dynamic loads, asymmetric deformations and track components damage and as a result, it increases maintenance costs. In this paper, the most widely used methods for stiffness transition are investigated, including concrete approach slab, hot mixed asphalt layer, stabilization and improvement of transition zone embankment. Then, the innovative combinatorial methods including improvement of transition zone backfill (embankment) materials with resilient pads under sleepers and rails on the deck based on specific criteria according to the finite element model. The results show that despeite various stiffness transition methods, the track according to the rail vertical displacement, ballasted layer vertical displacement and stress in the middle of the subgrade layer states has more desirable behaviour by about 14 to 22 percent, 3 to 29 and 4 to 36 percent respectively, rather than there is no stiffness transition in transition zone. Based on dynamic analysis, rail dynamic vertical displacement, rail dynamic vertical acceleration and force in subgrade layer is decreased by about 11 to 17, 32 to 40 and 1 to 22 percent respectively. Finally it appears that a combinatorial transition method include improved embankment in transition zone with resilient pads under the rail for rail on deck improved track behavior based on the criteria the rail vertical displacement and ballasted layer vertical displacement about %31, also decreased the normal stress in the middle of the subgrade layer approximately %28 and based on dynamic analysis, rail dynamic vertical displacement, rail dynamic vertical acceleration and force in subgrade layer is decreased by about 21, 34 and 23 percent, respectively. This method can provide the best impact and performance between different methods for concrete short span bridge and the relative displacement reduced in transition zone from 0.55 mm to 0.11 mm.