Post-tensioned domes designed to support stored materials can be built using inflated forms.

PREPARING THE FORM AND REINFORCEMENT

Reinforced base walls or other foundations must be prepared first. The vinyl-coated balloon is anchored to the foundation and inflated to desired shape at a pressure of about 12 pounds per square foot (psf). Harness cables laid out radially on the form before inflation control shape and provide some prestressed reinforcement. Conventional reinforcement, both bars and welded wire fabric, is then placed over the form in all but the uppermost part of the shell. Air pressure is increased to about 28 psf just before shotcrete is applied.

SHOTCRETING IN TWO LAYERS

Shotcrete is applied, working up from the bottom, in two layers. The first or scratch coat is about 1 1/2 inches thick. When the scratch coat is about halfway up the dome, pressure is increased to about 35 psf and held there until the project is complete. The second coat of shotcrete, about 2 inches thick, receives a float finish.