Night Shift on the Appian Way

Motorists travelling along the Appian Way through the scenic Blue Mountains will no longer be as frustrated, with one of the major bottlenecks eliminated. A new bridge, crossing the Great Western Highway at Woodford Bends, provides local traffic access over the highway.

The dramatic new bridge spans 20 metres above the highway and involved massive cuttings being excavated through sandstone ridges.

Innovative construction techniques were adopted by the Roads and Traffic Authority of NSW for this project including erecting steel girders at night under floodlights to ensure complete safety and minimise disruption to traffic.

The design of the bridge, spanning 44 metres, was carried out by the Authority's Bridge Branch and comprises twin steel troughs with a composite reinforced concrete slab deck.

Steel troughs were chosen for quick erection to minimise traffic disruption and eliminate the need for falsework which would have been impractical given the bridge height and highway volume.

Simple detailing for the steelwork made fabrication a relatively simple task. The trough girders comprise unstiffened flanges with minimum web stiffening. internal bracing was designed principally for support during erection and construction of the deck.

External bracing between the troughs is provided only at the abutments and consists of a 300 x 200 x 5.6mm RHS.

Surface treatment consists of a zinc silicate primer applied to all surfaces after abrasive blast cleaning followed by two coats of epoxy coating to the interior of the troughs and two coats of 100 micron thick cloud-grey chlorinated rubber to the exterior surfaces. Internal access to the troughs is conveniently gained from the northern abutment through doors at the end of the girders.

The 220mm thick deck comprises Transfloor permanent formwork decking, topped by a cast-in-place slab. The prefabricated panels were 2,395mm wide and the length varied from 9,000 to 11,000mm to suit the varying widths of the bridge.

Decking provided a ready-made, safe working platform for site work and allowed safe and uninterrupted passage of traffic below. Additional support for the cantilevered Transfloor decking at the flaring during construction was provided by a beam suspended above the deck. The decking allows full composite action with the cast-in-place deck slab resulting in efficient overall use of materials. The barriers were cast in place using mobile formwork.

The steel trough girders weighing 50 tonnes each were fabricated, transported to site and lifted into position on rubber bearings utilising a 200 tonne crane during the night.

The Project Manager and Superintendent's Representative, Mr Tony Booth, said, "The design and innovative construction techniques used on this project made the job easy. The use of steel avoided any temporary falsework and was a major factor in reducing costs and in maximising safety. The finished bridge has a clean smooth soffit and will be easy to maintain".