Engineers harness advanced software to deliver what is believed to be an Australian first: a single-span, integral steel trough girder bridge on a busy freeway. By Joshua Hoey.

Melbourne's CityLink Tulla Widening

project is a $1.3 billion upgrade to

one of the city's most heavily used

stretches of freeway. From Power Street

in Southbank through to the Melbourne Airport in

the North-West, 24 km of the CityLink, Calder, and

Tullamarine freeways are being upgraded. The project

is set for completion this year and will boost capacity

by 30 per cent with additional lanes, upgraded

intersections, new bridges, and a new freeway

management system.

As part of the project, the design joint venture

is handling design from Bulla Road near Essendon

Airport north to Melbourne Airport, a section which ,

includes the redesign, demolition and construction

of English Street bridge. The bridge had to be

lengthened and converted from a double span to

a single span to accommodate additional lanes in

either direction, and at the same time widened to

accommodate additional lanes on the bridge to

increase capacity to Essendon Fields.

As part of the requirements VicRoads stipulated

an integral structure. "Their big push at the moment

is to reduce maintenance, so a lot of projects now

have a clause calling for integral structures where

possible,· says Liam Thompson, Arcadis Senior Bridge

Engineer. "By eliminating bearings and expansion

joints completely, you remove the two most

maintenance intensive elements, reducing the whole

of life maintenance cost of a structure," he says. The

design joint venture went for an integral steel trough

design - the first of its kind in Australia - built to

AS5100�2004, so able to handle 160 t vehicles in each

lane across the width of the bridge.

But the site is significantly constrained by a

tramline running along the western edge of the site

along Matthews Street. "That was our main limiting

criteria, trying to get as little interaction with that

tram line as possible," says Thompson. Along with the

clearance requirements over the freeway, this meant E!l

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The removal of the bridge's central support (left) helped add more lanes to the road (below). -

PROJECTS -

do detailed 3D modelling of reinforcements as for English Street; he says. "For a Y-shaped pier on the previous M80 project, we modelled everything in 3D, including full pier reinforcement details, steel girders, drainage, and pits," he says.

Critical locations

MicroStation's clash detection is flexible, and can be performed based on levels, \ayers, elements or groups of elements. "We don't do clash detection on every piece of reinforcement in the structure, only at critical locations: precast to cast in-situ elements, stitch connections between decks and barriers," says Ryanto. At English Street, the critical location is the integral abutments to the piles and deck diaphragm, as well as the steel girder connection to the abutment diaphragm. Detailed modelling and clash detection was also performed on the trough girder connection.

In order to meet the tight schedule, the Arcadis and WSP team also modelled and performed clash detection for connections between precast crossheads and the bored piles, with 15 mm of

"Getting it right virtually was

critical if we were going to get

it right in real life."

tolerance. In the end, the fine tolerance proved to be a problem for the piling contractor, as they normally work to tolerances of around 75 mm, so the design was changed to a cast in situ crosshead. "It would have been great to see, because we did a fair bit of work on it, but unfortunately they weren't able to do it due to the limited tolerance," says Thompson.

As part of the project, VicRoads also required the design joint venture to use TeamBinder to share designs and modelling with fabricators and other contractors. Sharing modelling and designs across software allowed the piling contractor to identify the issue with tolerances. "We gave them the design IFC [Issued for Construction] and that's when they had a look and said 'we can't do in-situ piles with these tolera�ces,' which let us plan for cast in situ instead," says Thompson.

Ultimately the bridge went up in half the time without a hitch. Anyone who arrives into Melbourne has to drive under its wide, steel-girder span on the way to the city "There's no other way," says Ryanto. •