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Tuesday29 July 2014

Steel structures

Nunawading station, Melbourne

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Grimshaw used prefabricated steel units to provide high-speed construction without disrupting services from a suburban Melbourne station

Architect Grimshaw
Location Nunawading, Melbourne, Australia
Completed January 2010

Taking only six months from conception to completion, the rebuilding of Nunawading station is Grimshaw’s fastest project to date. The highly complex road and rail separation project needed to minimise disruption to transport users during implementation and adopt the shortest possible construction period, and this could only be achieved by using steel.

“We had to consider what material was appropriate and what was possible in the time frame given and steel fulfilled the criteria,” says Grimshaw associate Peter Stevens.

“Steel can be rapidly fabricated and has the flexibility to be erected in large scale elements.”

With the first passenger train running from its new station on January 11 this year, the AU$140 million (£80 million) project provides new station facilities, an elevated concourse and pedestrian connections to one of the busiest suburban rail lines in Melbourne.

The Belgrave-Lilydale rail line provides commuter rail services to central Melbourne and is punctuated with some 12 level crossings. One of these was near Nunawading station at Springvale Road, a six-lane north-south link in the eastern suburbs which some 50,000 vehicles use each day.

More than 218 trains pass through this level crossing daily, and the Royal Automobile Club of Victoria recently rated it as the most dangerous in the state of Victoria. This made the station’s redesign, including replacement of the crossing by taking the trains under the road, a priority in Victoria’s overall AU$38 billion (£22 billion) transport plan.

Station structure and access

The first pile placed in the ground on July 29 last year marked the beginning of the complex redevelopment of Nunawading station.

Originally opened in 1888, the station contained two side platforms, one with a fibre cement sheet clad station building and the other with a timber weatherboard building.

As well as demolishing the existing buildings, Grimshaw’s project involved the removal of the level crossing from Springvale Road by lowering the train tracks by 8m and the construction of a new road bridge spanning the lowered rail line at road level. The two platforms have been replaced by one 135m-long island platform situated below a street-level concourse accessed by stairs or a lift, all sheltered by soaring steel framed canopies.

A 60m-long pedestrian underpass has been created to provide station access from either side, which lets pedestrians avoid crossing the six lanes of traffic at the site of the former level crossing.

To avoid a potentially gloomy underpass, the design team created a light-filled area by integrating voids within the concourse level with a central spine of high-quality perforated timber panels. Daylight filters in through ETFE pillows fitted to the concourse canopy directly over the voids.

The four main steel-framed station buildings, together with the steel components to the concourse canopies, had to be prefabricated off-site in order to meet the exacting time schedule.

The incredible achievement of this project, apart from the speed with which it was executed, is that both Springvale Road and the railway line were open for almost all of the six-month construction period.

The only exception was a 10-day closure of the train line over the Christmas period to allow final construction of the lowered rail, and a five-day closure of the road when the bridge deck concrete was poured.

Steel Buildings and Canopies

Steel proved to be the only viable contender for constructing the station’s buildings and canopies for several reasons. It was quick to procure, easily prefabricated, able to achieve elegant and low depth structures and large spans, and able to deal with movement during erection.

The prefabricated modular station amenity pods were completely fitted out internally in the factory and transported to the site by heavy road transport. The units were then assembled into the final building configuration. The pod on the north side of the concourse provides station support while the pod on the south side accommodates station operations.

The largest primary steel frame unit was 16m-long x 6m-wide and 4.5m-high. The units were clad with highly robust, deep blue, vitreous enamel panels, the largest being 2.4m x 0.8m. The panels are extremely resistant to scratching, and graffiti can easily be removed.

The two main canopies on the concourse – the larger western canopy at 48m x 20.6m and the eastern canopy at 23m x 13m – are supported by 8m-high, 300mm-diameter tubular steel columns.

“The reason for the vaulting roof form for the canopies was to achieve a dialogue between the western and eastern sides of the roadway and to be of a scale that was appropriate to its context,” says Grimshaw associate Peter Stevens.

Standard profiled metal roof sheeting covers the canopies and Tasmanian oak timber sheets 2.4m x 1.2m were screwed to the soffits to provide an inviting high-quality finish and to conceal the steel connections.

Two clear, fully welded, ETFE pillows were joined together creating a 24m-long x 7.7m-wide skylight. These were fitted into the main concourse canopy on the western side. ETFE was used to maximise the daylight while providing shelter from inclement weather and to provide for the relative movements of the roof structure.

There is also a 90m-long steel canopy supported by tubular steel columns, which provides about 60% coverage to the island platform. At its widest it is 8m, tapering down to 3.5m and like the other canopies it uses standard profiled metal roof sheeting with a timber lined soffit.

Project team

Architect Grimshaw, Client Springvale Road Rail Separation Alliance, Structural engineer Arup, Bridge and rail engineer KBR, Services engineer Arup, Main contractor John Holland, Prefab buildings Precom, Enamel cladding HH Robertson, Canopy steelwork fabricator Macfab Engineering, Canopy steelwork shop detailer JBD

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