The construction is a prestressed 8-masts shaped membrane structure, designed to be used for travelling shows (no permanent installation allowed). It’s realised by means of a pre-tensioned single-skin membrane (divided in 10 sectors) supported in the centre by an 8.5m diameter cupola, and sustained by 8 masts, and tensioned at the perimeter by tied-down side posts. The membrane is the waterproof covering element and transmits loads to the structure (cupola + masts + up-winding cables) which supports it. The tensioned structure is closed on the sideways by side walls 5.0m tall.
The Big Top has been calculated for TEMPORARY use by adopting ASCE 7-10 wind loading standards as the guideline for wind pressure calculations.
Covered surface: 2.820 m2
Surface of membrane: 3.750 m2
The membrane geometry has been shaped starting from the plan and altimetric disposition agreed with the client using a graphic interactive program of calculation which allows to investigate the initial condition (status 0), realising a mathematical model and imposing equilibrium to a system of trusses and nodes. The structural model has been then analysed to find generated stresses and deformations with the FEM method using the software Straus 7 (certified by C+G Computing) with a non-linear static analysis.
The membrane is realised with a polyester fabric high tenacity coated PVC type 2, reinforced in the top part to resist local stress concentrations. The membrane joints have been realised by means of welding presses with an high-frequency system which makes the material melt with an automatic control system of power. Weldings are tested at 70° C, critic state of the membrane exposed to sun radiations.