Collins Street Bridge - more street than bridge?

To achieve this vision, a number of infrastructure connections need to be made between the Melbourne CBD and the waterfront. To date a pedestrian bridge has been constructed from the intersection of Bourke and Spencer Streets, linking the city to Colonial Stadium. However the extension of Collins Street, incorporating a bridge over the railway line, will complete this connection.

The Docklands Authority awarded Thiess Pty Ltd (Thiess) the design and construct contract for the Collins Street Bridge in May 2001, with work commencing on site in June that year.

Since then Thiess has made significant progress on this 350m long 12 span bridge that incorporates a tram line and two 3m wide traffic lanes, a 3.89m wide shared parking and cycling lane, and 4.9m wide tree-lined footpaths on both sides.

A section of the historic Goods Shed No. 2 has been demolished to allow the bridge to pass through, and the remainder is currently being used as a casting shed for the 99 I-beams (up to 80t) being cast on site by a joint venture between Thiess and VSL Prestressing Pty Ltd. The Goods Shed will eventually be converted to a markets precinct, with access from the bridge, and a tram stop at the access point.

A key feature of Thiess' design was the use of nine post-tensioned I-beams per span, with precast deck sections between them and a deck slab cast over this, in preference to using 13 Super T beams. This method provided faster erection time - a critical factor with restricted lifting access over the rail lines.

One span of beams is currently being cast insitu as an irregular soffit profile is required to allow a clear line of sight between the two remaining sections of the Goods Shed. This profile was difficult to achieve using precast methods.

The piers supporting the bridge must be placed at irregular intervals, and on irregular alignments, to fit in with the existing rail alignments, which means that each beam is different in shape and length, so that casting forms need to be reshaped after each use. A unique feature of the bridge is the use of trough-shaped girders on the outside.

The troughs are lined with welded HDPE and filled with soil. Services (including irrigation and drainage) will be buried in the soil, with trees planted at 12m intervals. A deck will then be cast over the top of the trough so that effectively the bridge has box beams along each side providing considerable strength and rigidity after post-tensioning.

The beams have been loaded onto a heavy load trailer by a heavy lift gantry and transported to the bridge site on a trailer. Most beams are being placed by Sergi's 250t Sumitomo crawler crane but on one span where this crane could not gain access Highrig Cranes supplied a temporary bridge that was placed across the incomplete span to allow the beams to be transported into a position where they could be lifted by a 120t and a 250t crane in a tandem lift.

Considerable attention has been paid to the appearance of the bridge. Precast bridge parapets are being painted silver, and will have distinctive round lights mounted on the outside. The beams are being painted charcoal and the crossheads are being painted red, giving an impression that the bridge is 'floating'. Poles with distinctive 2m long yellow lights are being placed on the bridge.

Future buildings will abut the bridge to give the illusion of continuity to Collins Street, which will eventually extend to the river.

The greatest challenge to the project has been obtaining access to the work area with only three rail track closures, of relatively short duration, being allowed while beam lifting takes place over rail tracks. A busy road also intersects the work area. It was necessary to close the intersection of Spencer and Collins Streets for a weekend in late March to allow tramlines to be laid across the intersection to join with those on the new bridge.

The bridge is scheduled to open in January 2003.