Sydney's Anzac Bridge is a high level crossing carrying six lanes of traffic and a combined pedestrian/cycle way. The divided traffic carriageway spans Johnston 's Bay, linking Sydney 's CBD along the Pyrmont peninsula with Victoria Road and the start of the City West Link at White Bay .

This 805 metre long concrete structure replaced an existing low level steel truss swing span bridge, built in 1903, whose four lanes could not support the demanding volume of traffic in this rapidly redeveloping area.
     
  Comprised of six spans with three cable-stayed central spans - hosting an impressive 345 metre main span - the Anzac Bridge is the longest span cable-stayed bridge in Australia.

The initial design was a two cell prestressed concrete box girder with three main spans (125 metres, 200 metres and 125 metres respectively) built with the balanced cantilever method. However, as most of the water's commercial and pleasure craft use no pilot or tug, the potential environmental impact of a pier collision with possible subterranean damage, was deemed unacceptable.
 
     

The most effective solution was to increase the span length so that the main piers were positioned out of the waterway. The structure adopted comprised three main spans (140 metres, 345 metres and 140 metres) which are cable-stayed and continuous with three prestressed concrete twin box girder end spans.

Approach piers were designed to be economical and effective within the constraints of horizontal alignment and available land use with minimum disruption to traffic during construction. The piers consist of conventional reinforced concrete columns supported on reinforced concrete piles or, where rock is near the surface, on reinforced concrete footings. Construction of the 20 metre high reinforced concrete columns for the approach spans was carried out in three lifts.

Each pier required 2835m 3 concrete and was completed as a single operation in a 24 hour period by Hymix Concrete. Over a weekend in September and done in November 1990, single continuous concrete pours incorporating Boral's Marine Cement were poured at an average rate of 120m 3 per hour, up to a maximum of 180m 3.

The Anzac Bridge towers and decking were constructed using concrete incorporating Boral's Shrinkage Limited Cement. Four concrete pumps were used at the height of each pour. With such a large mass of concrete, it was necessary to alleviate any problems caused by differential cooling of the concrete. Monitoring of the internal temperature of the pile-cap showed a maximum temperature of 80 degrees.

     
  The main features of the substructure are the two delta-shaped reinforced concrete towers approximately 120 metres high with a maximum width of 44.23 metres. The 32.2 metre wide superstructure of cable-stayed spans is a prestressed concrete open grillage deck system, comprising two longitudinal edge beams, cross girders at 5.17 metre spacings and a deck slab of 0.25 metre thickness. Construction of the cable-stayed spans is by cast-in-place free cantilever erection.

Construction of the tower legs commenced when the base segment of each tower was complete. The base segments consist of a solid block of concrete, 5.5 metres high and 6.5 metres wide, poured in two halves. The second segment was constructed with formwork tied back to a triangular frame anchored to the top of the base segment of each tower.
 
     

A jumpforming system - a structural steel frame supported by the previous segment - provided a safe environment to undertake formwork, steel fixing and concrete pouring operations. The jumpform was anchored to the previous segment by anchor bolts, then was elevated to the next segment with screw jacks once the concrete reached a strength of 20 megapascals. Threaded rods wound through the crossheads, attached to the jacking beams, and pulled the jumpform upwards.

The jumpform was supported from the previous segment by the legs of the screw jacks. Construction of the tie beam commenced once the two jumpforms were sufficiently apart from one another. The post-tensioned tie beam was built in five segments with each segment requiring two concrete pours. The upper tower legs and the tower head were also built with the jumpform.

Construction of the cable-stayed deck commenced with building the pier table on falsework. The deck was then erected by the cantilever methods, using a form traveller on one side of the pier (ie. water side) and a rolling form on the other (ie. land side). The form traveller was supported by the previous deck segments and the leading pair of stay cables. The form traveller itself supports the formwork for the next cast-in-place concrete deck segment. To reduce the weight of the form traveller, the concrete slab between the two edge beams was cast half a segment behind the edge beams.

The typical cycle for construction of a deck segment consisted of launching the form traveller to a new segment position; setting the formwork; installing and tensioning a new pair of stay cables; placing the reinforcement; pouring the concrete; and transferring the load in the stay cable from the form traveller to the new segment. The vertical sided 'T-beam' shape of the skeletal concrete cross girders aided formwork removal.

During the preliminary design phase, alternative structural systems for the cable-stayed spans were investigated. Composite steel plate cross girders were rejected due to anticipated high maintenance costs, fabrication complexities and the additional construction operations required.

Concrete, made with Boral's Shrinkage Limited and Marine Cements, addressed these issues by delivering the strength and cost efficient quality to successfully complete the Anzac Bridge.
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