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Architect : Grimshaw Jackson JV         

Structural Engineer : Winward Structures

Services Engineers: Lincolne Scott Australia

 

 

A   roof of shimmering zinc-coated aluminium billows across the platforms of Southern Cross Station in central Melbourne. The station is part of an AS$350 Million redevelopment which unites the rail and bus terminals and was completed in time for the 2006 Commonwealth Games. The surrounding urban landscape has been reconfigured so the station acts as a link rather than a barrier between the central business district and the docklands.

 

 

 

The   undulating profile is designed to remove diesel fumes without the need for a costly mechanical system. Ventilation lanterns at the top of each dome allow the wind to draw out fumes by Venturi effect. Heat build up under a single skin metal roof would cause disturbance to the air flow, so an inner lining of faceted 200 mm thick triangular panels has been installed between the steel bracing to effectively insulate the roof. Air is drawn up through gaps between the ceiling panels into a void between the inner and outer layers.

 

 

 

 

The   outer roof skin is curved in two directions using tapered strips of zinc-coated aluminium. Equipment was brought from Germany to roll the strip metal on site. To achieve the tight curves the strips were passed through the rollers four times in batches of fi ve or ten strips, each batch with a slightly different tapered profile. This complex process was only possible because the roofing sub-contractor was appointed at the detailed design stage to develop fabrication details alongside the architects, a process Grimshaws say worked remarkably well.

 

 

 

The   main structure is steel. Curved roof arches span up to 40 meters between trusses that are in turn supported on concrete  filled steel columns. The long spans reduce the number of columns required allowing for future flexibility or re-arrangement of the platforms beneath. 900 mm wide gutters either side double as maintenance walkways. Above the trusses 20 meter long ETFE pillows provide natural light on the platforms. The ETFE is fritted to reduce heat gain from the summer sun bathing the platforms in a cool forest floor light.

 

 

Drawing labels :

 

 

 

 

1.     Typical column    

 

10  mm thick circular mild steel (MS) column casing bolted down to concrete plinth. Casing tapers from 2000  mm diameter at base to 1180  mm at top. Height varies from 6 m to 12 m. Casing filled with concrete by pressure pumping from base once bolted in place.

 

Level 1 Plan – 1:500

 

 

2.     Wishbone column arms

 

Tapered arms made from varying thickness steel plates welded at edges with internal 6 mm thick diaphragm stiffening plates at 1250  mm centres.  1000 mm diameter 16 mm thick circular hollow section (CHS) welded through base of arm for connection to column. CHS connector located in column head and welded in place prior to filling column with concrete.

 

3.     Spine truss

 

Steel truss brought to site in prefabricated 4-bay sections. 356 mm diameter curved top and bottom chords. 356 mm diameter curved top horizontal member. 273 mm diameter vertical members. 219 mm diameter horizontal diagonal braces. 168 mm diameter diagonal braces either side of column connection. Three pin connections on truss prefabricated and site welded to each column arm.

 

4.     Roof steelwork

 

356 mm diameter MS primary roof arches curved to form undulating roof profile. 168 mm diameter MS lateral struts bolted to cleats welded to arches. 168 mm diameter MS diagonal braces bolted to 356 mm diameter bosses welded to arches. 76 mm diameter MS posts with brackets to support roof panels and cladding rails welded to primary arches at maximum 1500 mm centres.

 

5.     Ceiling panels

 

200 mm thick prefabricated triangular panels bolted between diagonal braces to cleats on MS posts. Panel frame made from 150 x 75 mm galvanised light gauge steel channel sections. Profiled galvanised steel top sheet. Joints between panels covered with reinforced plastic strips. 1.5 mm thick polyester powder coated aluminium panels to underside to form finished ceiling. 100 mm gaps between ceiling panels above truss chords and primary arch to allow fumes to be drawn into roof void. Bird mesh fixed to rear of ceiling panels over gaps.

 

6.     Cladding support rails

 

114 mm diameter curved aluminium rails bolted to MS posts to support roof cladding.    

 

7.     Roof cladding 

 

Tapered 1 mm gauge zinc-coated aluminium standing seam roof cladding clipped over proprietary supports. Continuous void between roof cladding and ceiling panels to allow fumes to be drawn up to ventilation domes at tops of arches.

 

 

Diagram showing natural ventilation via roof cowls

 

 

8.     Gutter

 

200 75 mm parallel flange channel (PFC) and 200 x 200 mm universal column (UC) gutter frame bolted to steelwork at each primary arch. 930 mm width 20 mm plywood gutter base bolted to steel frame. Non-slip single ply membrane gutter lining to act as maintenance walkway. 4000 x 700 x 220 mm deep sump with two outlets at each column position. Folded 2 mm aluminium vertical cladding to conceal gutter below rooflight. Two 125 mm diameter rainwater downpipes running down each column arm and cast into concrete trunk of column. One electrical conduit in each column arm running up into ceiling void.

 

 

 

Typical Gutter Section – 1:40

 

9.     Rooflights

 

20 metre long ETFE pillows running along full length of roof over spine trusses with 18 mm diameter white frit over 60% of surface. Extruded aluminium perimeter clamp plate bolted to UC gutter structure. Clamps at ends of ETFE pillows made from back-to-back angles to form expansion joint.

 

 

Cut-away view of typical column, truss, rooflight and roof