In Central Park Sydney, a 12 metre diameter shimmering yellow ring hovers 13 metres above the crowd. ‘Halo’ is a contemporary kinetic sculpture conceived by artists Jennifer Turpin and Michaelie Crawford, commissioned by the City of Sydney as part of a $8 million beautification project for the park.
Jennifer describes Halo as… “an extraordinary integration of art, science and engineering, acting in collaboration with the natural environment.”
Halo is a feat in carbon composites design and collaboration. Taking three years to complete and costing over a million dollars, the project was led by Partridge Event Engineering, with input from SP High Modulus (now trading as Gurit). The final structure was built, tested and erected by Innovation Composites, with further assistance from MouldCAM and Aptec Composites.
Mark Rowed of Innovation Composites said the aim was to interpret the vision of the artists, inspired by the old brewery.
From an engineering perspective the goal was to create the lightest, strongest and most friction-free sculpture possible using carbon composites. The site usually only experiences a gentle breeze, however the circular structure needed to move from this energy source alone.
Project leader, Jeremy Sparks, from Partridge Event Engineering said mechanical, structural, carbon fibre and wind engineers all collaborated.
“Partridge Event broke new ground, using a risk management process to identify opportunities and ensure optimal outcomes. All disciplines achieved better than expected results, acknowledged by the prestigious President’s Prize at the Engineering Australia Excellence Awards for 2012,” Jeremy said.
Mark Rowed said, “The artists did have to modify some of their ideas … Mostly with little things like the joining sections. They wanted them a lot smaller, to look as though there was just this ring floating in the sky”.
The structure – comprising a 13 metre high supporting steel mast (composite coated), a carbon fibre arm and a tapered carbon fibre circle – had to be constructed and transported in segments.
“To create the actual tapered circle, the carbon fibre was vacuum consolidated in female moulds in the ring in sections, which allowed three to seven hours of working time. This ensured a very strong and light-weight result. Female moulds were CNC cut by Mould Cam, Queensland, into segments and halves,” Mark said.
“”We needed recessed flanges, so then we joined each of the three segments to form a round … The outer segment was joined up later with carbon fibre.”
For the Halo arm, Aptec Composites machined a solid female MDF mould and Mark’s team bladder-blew and vacuumed a mono-composite structure, using carbon prepreg for greater strength. (This remained in a gel state before heating at 90° C to cure.) A high temperature liquid release was used, plus a stretchable bag, as the arm was a highly complicated shape.
A challenge occurred with the heel section, where the arm connects to the main ring. This required a stainless steel duplex joiner to be bolted through the carbon. There were more than one hundred counter-sunk high tensile steel fastenings through the carbon and extensive analysis was required.
Mark and his team did a week of testing at Nowra South, with cranes on-hand.
“There were certainly some hearts palpitating when it came time to join it up! We also had to make custom tents over each join to keep the weather out … Overall it went smoothly,” he said.
It was cut into thirds and “sent to Sydney on two semi-trailers, put on like bananas with the ends pointing to the sky, on a
The artists were involved in each stage of the process, but especially in the final finish. This required up to 30 applications –
including undercoat, primer, yellow base-coat and pearl high-end automotive paint (in several shades), plus two final coats of clear urethane. The final painting was of the joins, onsite in Sydney. After curing for 28 days nanotechnology wax was applied over the entire surface to protect it from grime.
“We estimate it took us six months … three-to-four months of actual building – approximately 5,000 hours in labour,” Mark said.
Halo has inspired a new generation of artists and composite engineers and generated leads for Innovation Composites from the Randwick Women’s Hospital and also for the upcoming Winter Olympics in Russia. The opportunities from combining functionality with aesthetics are now truly staggering!
Below: Creating the the lightest, strongest and most friction-free sculpture possible using carbon composites – Halo