DomeShells First Full-Scale Prototype 8.0m Dome
This 8.0m diameter dome shell was built in 2002 after a year of materials property testing and finite element analysis in collaboration with Queensland University of Technology Brisbane.
The dome is built on private land near Stokers Siding in Northern New South Wales, Australia and is used by the property owner and his family and friends who often stay in the dome.
8.0m Diameter Dome Slab
This is the slab setup for Domeshells very first full scale prototype. Except for the perimeter of the slab where the wall of the dome will be, the whole slab is completely covered with plastic which is taped down around the edges.
The window/door frame that will be cast into place in the shell, are lying on the slab at the position they will be stood up.
A steel channel holds down mesh around the perimeter edge of the slab. The mesh will be cast into the composite wall of the dome.
The air form is made of a flat sheet of rubber 1.5 mm thick fabricated for the job. It was a trick to gather as much of the flat sheet into the middle of the slab as possible to create a big balloon when we inflate it.
The rubber is inflated by a fan driving air through a 100 mm pipe cast into the slab, from the edge of the slab to the centre. The height of the balloon is adjusted by a wire connected from the apex to a butterfly valve at the air inlet so when the fans are turned on the system self regulates the airflow keeping the balloon at a consistent height.
The inside of the air form is accessed through the doorway into a double air-lock. In side there are two air-tight chambers so that entering and exiting from the inside of the balloon does not affect the air pressure.
Standing Window Frames Against the Air Form
Inside the air-form. One of the window/door frames is stood up against the air form. The base of the frame is bolted to the slab. The frame is propped with adjustable steel props bolted to the slab top keep the frame plumb.
A timber face over the steel prevents any possibility of tearing the balloon with the steel.
The alkaline resistant glass mesh is folded out of the way of the edge of the frame which will be encased in polyurethane foam. Prior to commencing the spray foam the glass mesh will be completely masked to protect form polyurethane over spray.
Around Window Frame After Spraying Polyurethane Foam
This is how it looks after the polyurethane foam has been sprayed and all the over spray has been cleaned away.
The undulating foam has also been planed and sanded to an even finish in this case to a minimum of 55mm.
The whole of the dome inside the air form has a layer of 55mm foam sprayed in place and all the window and door frames are cast into the foam.
It is now ready for the internal layer of "glass fibre reinforced concrete" (GRC)
Spraying GRC on the Inside of the Dome
Spraying GRC on the inside of the dome. In two layers a thickness of 8mm is built up and trowelled off to as smooth a finish as possible. GRC formulation of 5% fiber is too much fiber to get a good trowel finish. The best way to achieve a fine trowel finish is to apply another layer of about 2mm of render without fiber.
If a white cement is used for the final coat it leaves a very nice finish and immediately lightens up the inside of the dome
Trowel Finishing GRC
Always best to get a continuous coating all over in one go.
Crew should be big enough to comfortably finish two layers in a day.
The fans inflating the balloon are turned off after the foam is in place, however, the fans and the airlock system are fully operational during the application of the inside render GRC coating and stayed on for 24 hrs
A Polyurethane Foam Dome
The Foam Dome. The rubber air form is removed. Luckily we had a small crane to lift the air from off the foam (with GRC inner coating) .
The dome is in preparation for its outside skin.
Applying the outside layer of GRC. In this case, we use an off white cement.
Starting at the top of the dome we easily apply a generous 8mm coating. On the more vertical sides of the dome we applied 2 layers to achieve the correct thickness.
Internal and External Coating of GRC is Complete
The exterior of the dome is complete with an 8mm layer of GRC inside and outside of the 55mm core of polyurethane foam.
Now the dome is ready for physical load testing by the engineering lab technicians at QUT.
The outer skin is pierced by a series of bolts holding a grid of steel plates on the inside of the shell. To these plates are fixed powerful pneumatic rams which will from inside simulate the loadings of a cyclone.
Load Testing Time by QUT Brisbane
Technicians take 3 days to set up the equipment that will be used to load test the dome shell.
Countless strain gauges and electronic sensors taped to the walls are wired to a computer control panel to provide readings all over the shell as loads are applied by the rams bolted to the floor.
Compound Curved Sandwich Shell Structures
Domeshells passes all it's testing and may be certified under the 'Building Code of Australia".
The dome behaved under load exactly as the lab models had predicted - exactly!
Interior Wide Shot of 8.0m diameter Dome Shell
If you are interested in how this system works you can access a copy of a highly detailed manual here!