New Precast Concrete Portal Bridges for Railway Gauge-Clearance


Various Contractors for Network Rail

Project Description

This project information sheet describes eight online highway bridge deck reconstructions which were completed using precast concrete portal structures. The new portal structures were designed to replace existing masonry arches and to be installed on reused existing piers and abutments trimmed down to springing level. The new portals are of simple form, allow minimal depth construction (improving clearances) and mimic the structural behaviour of the existing thus justifying reuse of the foundations. The projects have been completed, at Oxford, near Winchester, on the Great Western Main Line and in Scotland.

Cass Hayward Role(s)

  • Options studies
  • Design of new and reconstructed underline bridges
  • Design of demolition schemes for existing bridges
  • Design and checking of temporary works

Projects Statistics

  • The designs have been completed for single, double and triple spans as suited to the track layout below
  • The spans have been of equal and variable lengths and in symmetric and asymmetric arrangements
  • Spans have been provided for single and double tracks up to a maximum length of 18m and set at skews up to 25°
  • Bridges have accommodated highways up to 12m wide including footways

Special Features

  • The designs are for a site assembly of precast concrete components providing the entire new structure comprising bridge spans, parapets, substructures and retention for the approaches
  • Where required for structural purposes adjacent components have interlocking reinforcement at site-filled joints
  • High containment parapets are provided at all bridges using precast concrete with a high quality feature finish, brick cladding or reinforced masonry
  • Components and their assembly are modelled in 3D CAD to help to ensure fit at site
  • Demolition procedures - especially for multiple span arches - are subject to special scrutiny at design stage so that suitable controls can be effected at site
  • Some projects have required extensive approach retention walls to accommodate higher embankments and parapet transitions