When performing railway track stiffness analyses, in current standards sleepers are often regarded as a rigid member. For flexible sleeper materials like timber or polymers, this may lead to underestimating rail deflections up to a factor two and overestimating rail seat loads up to 20%. Calculations incorporating sleeper bending can currently be performed analytically by a two-layer beam-on-elastic-foundation calculation, or by finite element analyses, but a simple approach does not yet exist. This article introduces a simple calculation method to establish rail deflections, track stiffness and rail seat loads, incorporating the effects of both bending and shear stiffness of the sleeper, applicable to new or tamped track. A sleeper flexibility factor f_S is introduced as a deformation multiplication factor compared with a rigid sleeper. Validation against current calculation models shows a deformation accuracy within 6% and a load accuracy within 2%. When a track is not maintained, a gap will develop under the sleeper at the rail seat. The size of this gap correlates to the stiffness of the sleeper. Eventually a uniform load distribution can develop under the sleeper. A calculation method is introduced to estimate the gap and the track behaviour at uniform load distribution. When for flexible sleepers the track deflection due to the gap can develop outside of the desired range, timely track maintenance or monitoring is advised.

This article deals with the fire safety test of polymer sleepers in the ballasted track. Although the occurrence of a fire in the track is unlikely, it may occur, for example as a consequence rolling stock fire or arson. In the past, old rolling stock assembly or track maintenance could lead to fire. For these reasons, products installed in track must be fire-safe. A new trend in the sleeper development is the utilization of polymer-based materials that suitably combine the beneficial properties of prestressed concrete and impregnated wood. In the recent developmental phase, polymer sleepers have been subjected to laboratory testing in which their mechanical resistance has been successfully verified. Nowadays, the polymer sleepers must be tested in their authentic environment and within train operations. This paper deals with an in situ fire test of chosen polyethylene sleepers, in which a fire in track was intentionally initiated. The aim of the test was to verify the possibility of spreading fire between sleepers in conditions of their application. Conclusions from the fire test are based on monitoring the temperature development by infrared thermography, thermocouples, visual inspecting fire spread, and wind direction and velocity monitoring by an anemometer. Justified by temperature monitoring no significant heat transfer between polymer sleepers was observed during the test. Therefore, the assumption about the insulation-like property of crushed stone was confirmed and the fire safety of polymer sleepers subjected to the fire propagation test between sleepers was demonstrated.

In ballasted track, the wheel load is transmitted to the subgrade via sleepers commonly made of impregnated wood, prestressed concrete, steel or recently developed polymer sleepers. Mentioned material types of sleepers are characterized by different elastic moduli being a key parameter in any numerical model. Hence, this paper aims to determine the elastic modulus of sleepers subjected to a laboratory four-point bending test. Traffic resembling load level of 60 kN adopted from a typical axle load distributed by the rails to the sleeper was applied in a quasistatic and cyclic loading. The samples included sleepers made of polymers complemented with wood and pre-stressed concrete. The results of this paper are based on the elastic modulus investigation. Main conclusions are focused on the sleeper's elastic modulus under changing loading frequencies. Wood and prestressed concrete sleepers indicated mainly elastic behaviour resulting in a constant elastic modulus. However, polymer sleepers showed a loading frequency dependent elastic modulus as a result of their viscous elastic behaviour. Moreover, the conclusions of this paper involve E-modulus measurements of impregnated beech sleepers in order to describe their piece by piece elasticity variation due to their natural origin.