Structural performance of prestressed precast high speed railway bridges using high performance concrete

Abstract

Bridges often need to conform to strict alignment rules for high speed railway (HSR) lines. Generally, the bridges are constructed either from prestressed concrete or steel-concrete composite. Prestressed concrete bridges can be constructed by precast methods, which offer benefits in economies of scale, quality and construction times for long repetitive viaducts. However, currently precast construction utilises conventional concrete strengths, leading to thicker, heavier cross sections to resist the load. High performance concrete (HPC), with its increased strength, can be implemented to reduce the precast segment weights, subsequently reducing substructure and transportation capacities. However, lighter sections could lead to decks more prone to vibrations exceeding acceleration limits. Therefore, the implementation of HPC requires further research, addressed in this thesis, using the most sophisticated and realistic numerical models of the bridge, vehicle, track, wheel-rail interaction and rail irregularities, identified in literature.

A suitable benchmark bridge is selected and analysed from a database of concrete HSR bridges. This analysis finds that using track irregularities with wheel-rail contact is mandatory for accurate bridge accelerations, leading to up to 3.75 times larger accelerations than equivalent moving load models. Furthermore, sectional deformations have been found to be non-negligible, with beam element bridge models incapable of exhibiting the wide frequency content of the acceleration response seen in shell elements. A subsequent parametric analysis reduces the geometrical cross sectional dimensions of the precast components, implementing HPC to maintain the structural capacities.

The applicability of the acceptable parametric analyses are tested on other bridges, determining more general conclusions for HPC inclusion in HSR bridges. Appropriate reductions in geometry (web, bottom flange and top flange thicknesses down to 66, 75 and 75% of the original value respectively), are identified from the response of the bridge and vehicle, by using HPC up to 96 MPa, contributing to up to 22% lighter precast elements. Appropriate design guidance is subsequently made for better design of HSR bridges to incorporate HPC into precast solutions.