BEHAVIOUR OF PIERS IN CURVED RAILWAY BRIDGES UNDER MOVING LOAD

Abstract

Historically railway bridges have been built only in straight providing curves on approach embankments. Wherever, curved bridges have been provided, curvature was too flat to produce any significant centrifugal force. The codes have accordingly provided for considering the centrifugal force as static force (=mv2/r). However, with the introduction of Metro Services which have to pass thro congested city areas, bridges with sharp curves have to be provided with high piers which is a significantly changed scenario than conventional railway bridges, however, no separate guidelines are available on the subject. Since the load from train is transferred to bridges substructure through rail wheel contact as moving point load instead of line load, the resulting action is a time variable load on substructure and hence its effect is more close to dynamic load than a static load. From the study carried out in Major Project-I, it has been noted that when centrifugal load is applied as a dynamic load instead of static load, the dynamic amplification in pier deflection and resulting internal forces depends upon train speed. Tendency of resonance has also been noted at a critical speed. The proposed study aims at studying the behaviour of piers in curved bridges by varying various parameters, viz., i) span length, ii) Weight of span, iii) Height of pier, iv) Size (Dia) of Pier and v) Speed of train by way of dynamic analysis. The results obtained will be compared with the results obtained from static method as per existing codal provisions. The combinations of span, pier height and train speed resulting in resonance or high amplification factor will be identified and recommended to be avoided for field application. The combinations not leading to resonance or high dynamic amplification factor within operational speed of trains will also be identified for safe use.