NQE was engaged by the world renown artist, Jason deCaires Taylor to assist with the design and certification of an underwater art installation off the coast of Townsville on the Great Barrier Reef.
The installation, known as the Museum of Underwater Art (MOUA), consisted of a coral greenhouse and a variety of stainless steel and concrete sculptures.
Even though the entire installation is submerged underwater, cyclonic wind events are the critical design condition for the installation. Waves can be generated by cyclonic wind speeds (165km/h to 198km/h for a 10min gust) which have the potential to reach 5 to 5.9m in height, respectively. This in turn creates lateral pressure pulses at the greenhouse level (6 to 18m below the surface) which must be resisted by the various structural systems. This phenomenon has been known to rip large bombers off the great barrier reef and "throw" them causing huge damage to the reefs in their path.
The greenhouse was the most challenging structure to anchor. The design envisioned by the artist was a light weight stainless steel exoskeleton in the shape of a greenhouse. This in effect created a large underwater sail for the lateral pressure pulses. It was estimated that these loads could be up to 10-20t depending on the direction and the wave height.
To mitigate these potential extreme loads, address the environmental requirements and associated risk of an "above design" event occurring, a two stage lateral restraint system was developed for the structure. The first stage involved stainless steel anchor rods, incorporated in the design to brace the greenhouse up to the 20t of lateral load limit. The second stage involved a secondary flexible stainless steel tether which was incorporated in the design to provide an additional safety mechanism in the event of partial or complete failure of the greenhouse structure during an "above design" event. This was designed for up to a 54t lateral load limit. The sole purpose of this secondary tether was to reduce the risk of the structure causing damage to nearby reefs in the event of failure from "above design" events.
The foundation of the greenhouse was designed as 4 precast concrete modules with a maximum mass of 30t each as per the requested limit of the installation crane and barge. These modules would be bolted together underwater at the installation location to form the final greenhouse foundation. The design featured a 600mm deep base frame that provided overall stiffness to the foundation. This frame was designed to be inherently robust and resistant to scour and differential settlement. On top of the base frame, 3 - 300mm thick slabs would be installed which provided the floor and support system for the approx 40t of sculptures that would be post installed on the foundation.
NQE provided concept development services, detailed design, foundation design drawings, professional certification and underwater, as built, structural SCUBA inspections and certification of the final installation. Partner companies involved in the delivery of the project included Reef Ecologic, Pacific Marine Group, Madsen Giersing and EDMS Australia.
Images by Gemma Molinaro from Reef Ecologic