Faber Maunsell claims to have completed the first replacement of a rail bridge in under eight hours and under overhead electrified lines in Gateshead.
As part of a drive by Network Rail to maintain a 24/7 railway, Faber Maunsell was commissioned to design a replacement for an underbridge (carrying rail, with a road underneath) using only the standard 8 hour “Rules of the Route Possession” regime.
Faber Maunsell assessed the structure initially and found that the existing structure in its present condition was significantly under strength and theoretically unable to carry the present capacity of the line. In response to this, the consultancy designed a replacement structure and methodology of construction which allowed for the rail bridge to be used 24/7 and without disruption to the trains and maintained access to pedestrian traffic underneath
“The presence of the 25kV overhead lines prevented a more conventional approach of constructing a new deck to the side of the existing bridge, and craning it into position,” said regional director of Faber Maunsell Paul Musgrave. “There was insufficient time to dismantle and re-erect the overheads within the 8-hour possession available to allow the use of cranes at track level so we had to look at a design where we built the supporting structure from underneath. Once the supporting structure was complete and the planned possession taken, the overhead lines were isolated to ensure the safety of the construction personnel carrying out the final ballasted track installation.”
The design comprises a reinforced concrete portal structure, on piled foundations, constructed between the existing stone abutments. The portal is built underneath and around the existing wrought iron girders, enabling the bridge to remain open to traffic during the construction works.
When complete this structure will be only the third ‘8-hour bridge’ replacement to have been carried out, and the first to have been undertaken under overhead electrification.