APPLICATION OF PROJECT:

The project was to supply and install a unique waterproof shade cloth structure over the old two lane Mandurah Bridge built in 1952 .

The old bridge was recently decommissioned to vehicles and replaced by a modern 4 lane bridge to cater to growing population and traffic needs of Mandura and the Peel region of WA. The old bridge with it timber and concrete undercarriage was to be partially retained and converted into an attraction.

PROJECT DESCRIPTION:

The area under cover is 207sqm. This is 9m x 23m.  The shade structure weighing ten tonnes with post masts up to 9m tall was built on the bridge platform using only the old piers as anchor points.  Eight posts were braced onto eight old piers. The structure comprises 6 intersecting PVC shade sails. Cut outs were incorporated in the patterning of the sails which enabled posts to poke through the structure at a height of 4m.

The head contractor was charged with building the new bridge and redesigning the old bridge. The Department of Main Roads was the principal client.

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DESIGN / FABRICATION / INSTALLATION BRIEF

After consultation with the community, the old timber fishing platforms on the undercarriage of the old bridge were to be partially retained. The bridge restoration and conversion was to be part of a boardwalk system with a nostalgic nautical character.

The clients brief was;

  • To build a shade structure as part of works to preserve sections of the old heritage bridge and become a local attraction.
  • That the shade structure design would mimic the colour and flight of the many sea birds in the area.
  • The shade structure be connected only to existing bridge piers.
  • Work with engineers and architects to convert the preliminary concept design into a structural and aesthetic shade structure.

STRUCTURAL SYSTEMS

The design does not have typical footings into ground. The structure could only be fixed to the old bridge piers. It could not be accessed by a land supported crane.

Though adding a layer of design interest an extra layer of installation complexity was the 2m x 12m water channel running through the centre of the platform and thus the middle of the shade structure work zone.

There were four main challenges and a hundred minor challenges to overcome.   These were transporting product across the country, accessing the pier, bracing to old piers and working above water.

Interstate transport.

To be in control of the fabrication process it was decided that steel fabrication, galvanising and blasting/painting and fabrication of the PVC membrane roof was to be done from Sydney. The structure components including painted steel and fabric roof were individually wrapped in carpet and tarpaulins.  An interstate road train delivered the structure across the Nullarbor to Mandura WA promptly and without incident.  This was a great relief.

Accessing the fishing platform

Originally, we planned to install steelwork and roof membrane from a crane located on the nearby new bridge 30m away. However, we missed an opportunity to use the bridge. 

While the new bridge, built over a 3-year period was opened in January 2018, the shade structure ordered in end 2017 was still in the design phase and a long way from installation.  The design had to be right.

Between WA Main Roads, Mandurah Council and the Head Contractor a crane would not be permitted to block a lane of the new bridge without significant fines being imposed so an alternate plan needed to be found by the head contractor.  The answer was to use a water barge with crane and this is what was used. Using a barge crane was a first for our company and quite possibly a first for a shade structure in our industry.

Bracing to the old piers.

The bridge contractor, Georgiou shaped and strengthened the eight old bridge piers in readiness for the shade structure bracing and framework to be installed.  Piers had to be cut down to 1m and shaved to a pre-determined size for the shade structure braces to wrap around the piers and make the whole project fit together.  While the preparation of the piers helped, on installation it was necessary to reshape the base piers with diamond grinders so that the shade structure bracings fit as securely over the piers as they had been designed to do.

Working above water- Water barge and floating pontoons.

Working from a barge over the water was fraught with risk and danger.  The barge was as big as a tugboat and subject to movement of water in the estuary. Anytime a boat came past, a slight chop in the water would reverberate to the crane hook and result in movement and swings of steel of up to 2m. Being alert was critical.

The barge which was the size large was fine in the open water outsides of the platform but was too big for the central two meter wide channel inside the fishing pier. Access into the central channel to position columns to tighten bolts was achieved by using a floating pontoon.  Again, any water movement impacted on the stability of the pontoon.

The edges of the work area for the structure were beyond the edges of the platform or over a central water channel.  Some, not all tools were able to be secured to lanyards on clothing. On one occasion a podge tool fell into the water below. Being only 2-3m deep this was an opportunity for the foreman to don his scuba gear, dive into the water and retrieve the tool. This was a moment of light relief in a stressful project.

MATERIALS

A 207sm shade structure adorns a fishing platform which was part of an old road bridge.

Built without typical footings the structure is braced and supported on eight modified steel bridge piers.

Mehlar Mehatop N 700gsm in white from Shann Accessories was used for the PVC roof membrane.

We use materials we know and can rely on. The fabric had to be able to play with light as lighting effects were a feature of the design. As a smaller structure a 700gsm fabric was able to provide the weather protection and cope the wind loads apparent in this coastal area of WA.

Steelwork was both galvanised blasted and painted white as required by the coatings consultant. Galvanising to a thickness to suit a coastal environment and to provide rust protection inside and outside the steel was stipulated. This process was followed by a blasting and a three coat durable painting treatment. Whilst no warranty is available on this treatment, a 25 year maintenance free period is expected.

FABRICATION

The 207sqm structure was covered with 6 smaller PVC roof skins.  Each skin used no more than 40sm of fabric. This made fabrication and handling of each textile component quite straightforward.  

OTHER INFORMATION

The structure is the crowning glory for this wonderful old bridge and foreshore restoration sensitive to its heritage and with a character that is charming and inviting.

A myriad of boardwalks links the fishing pier to the nearby waterfront shops. It is a glorious place to visit. It is a unique and welcoming space for fisherman, visitors and morning dog walkers alike. 

The shade structure is light enough that it could fly yet solid enough to last the roaring 40’s for many years

The project has exceeded all expectations and the fishing deck was opened to the public with much fanfare from local politicians. The shade structure incorporates colourful lighting every night which changes to suit the occasion.

Credits

Entrant:  Hytech Plastics pty Ltd t/as Abacus Shade Structures
Role played by Entrant:  Designer / installer

Location:  Mandura, WA 
Completed:   March 2018

Client:  Dept Main Roads

Architect:  Landscape Planners Pty Ltd, Abacus Shade Structures design
Engineer:  Structerre Consulting Engineers
Specialists:  Georgiou Civil Site Foreman
Builder:  Abacus Shade Structures
Fabricator:  Abacus Shade Structures