TRACK-BRIDGE INTERACTION IN PRESENCE OF CWR: STABILITY AS WELL AS STRENGTH ASPECTS

Abstract

A robust rail infrastructure is the backbone of a strong economy. Major rail tracks are shifting worldwide from jointed rail to continuous welded rail (CWR) due to its inherent advantages. Continuous welded rail (CWR) forms a long, smooth track without joints increasing train speed and passenger comfort while reducing tractive effort and maintenance costs. However, the stability of CWR has been a source of concern because rail being a slender structural element with low thermal inertia that absorbs heat quickly and tends to buckle. Rail breakage or track buckling can result in derailments, potentially leading to catastrophic consequences. When CWR track is supported on bridges, both track and bridges are subjected to effects of the track bridge interaction (TBI) phenomenon. TBI results in additional rail stress, track and bridge displacements, and pier forces. The distribution of the rail stress developed due to TBI varies significantly along the track-bridge portion of CWR, creating local high stress zones in the track. This stress development is in addition to the stresses developed in CWR due to daily and seasonal temperature variations. The interaction between CWR and bridge originate from temperature changes in track and bridge, braking and acceleration forces, and bending of the bridge deck due to vertical loading. The first two loading cases alone can contribute significant TBI effects. As the TBI phenomenon is influenced by numerous parameters, the evaluation of various forces and stresses is computationally intensive. A simplified methodology and a model need to be there to help the designer to estimate TBI effects. In this study, a simplified numerical model has been developed to study the TBI phenomenon and its influence on the stability of CWR due to temperature loading. With the help of the developed model, the nature, magnitude, and location of the of the stress developed in CWR due to TBI has been investigated. Also, the forces transmitted to the abutments/piers of the bridge substructure has also been examined. For assessing the safety of CWR against buckling, the nonlinear buckling analysis of CWR has been carried out considering the influence of TBI. the influence of TBI on the two critical buckling parameters of CWR, the maximum buckling temperature (𝑇􀯠􀯔􀯫) and safe temperature increase (𝑇􀯠􀯜􀯡), has been studied by developing the nonlinear buckling curves for various track-bridge scenarios. 𝑇􀯠􀯔􀯫 and 𝑇􀯠􀯜􀯡 are critical parameters affecting track safety against buckling and needs to be kept within safe limits to ensure the track safety. Further, the present work investigated various aspects of multi-span bridges for the development of TBI effects including the influence of span length, number of spans, support arrangement, and support stiffness variations. The present study highlighted the significant influence of bearing arrangement on TBI effects for multispan bridges. The location of the potential zone of track instability changed with the change in the bearing arrangement. The present study investigated the effectiveness of application of cross bracings in controlling the track buckling. An artificial neural network (ANN) has been trained to provide the designer with useful quantitative data about the phenomenon in real time. In this field, less quantitative information is available to guide the designer. Through quantification of TBI effects and behaviour studies, the current study helps the designers in design of new infrastructure as well as will be useful in assessing the suitability of CWR on the existing infrastructure for upgrading to high-speed tracks.