What this research found
A 50-metre-diameter reinforced concrete dome to roof a dance hall in Sydney was carried from geometry through to cost, using thin-shell membrane theory and checked against the Australian Standards. A 200 mm shell proved sufficient, peaking at 0.74 MPa of compression against a 14.4 MPa allowable, and the rough-order-of-magnitude build cost came to $2.11M AUD excluding GST over a 12–16 week programme.
- A 200 mm shell thickness is structurally adequate at 5.1% stress utilisation: peak meridional compression reaches 0.74 MPa against the 14.4 MPa allowed under AS 3600, leaving substantial reserve capacity.
- The dome's outward thrust concentrates at the springing, where an edge ring beam must resist 2,550 kN of tension. The design meets this with eight N32 bars in a 600 mm by 800 mm beam.
- The rough-order-of-magnitude estimate is $2,114,362 AUD excluding GST, or $928 per square metre of dome surface, with a ±30% range of $1,480,053 to $2,748,671. Direct construction accounts for 60.8% of that, indirect and professional services 22.5%, and contingencies 16.7%.
- Pneumatic formwork — an inflatable membrane instead of conventional scaffolding — is projected to save $615,000, a 60% reduction on that line item, and installs in 7 to 10 days.
- The take-off comes to 805 m³ of concrete and 76 tonnes of reinforcing steel across 2,278 m² of shell surface, with the shell poured continuously at 456 m³ in eight hours to avoid cold joints.
How it was done
Geometry was fixed at a 50 m span with a 10 m rise, a rise-to-span ratio of 0.20. Dead load of 5.55 kPa, live load of 0.25 kPa and a 0.55 kPa wind load for Sydney wind region B were then combined per AS 1170.0, giving a governing ultimate case of 7.21 kPa. Meridional and hoop stresses were computed from thin-shell membrane theory and checked against AS 3600-2018, after which material quantities, a pneumatic-formwork construction sequence, and a cost breakdown were derived. The result was written up as a 44-page technical report with ten figures covering geometry, load and stress distributions, reinforcement details, and formwork cost comparisons.
Data sources
- AS 3600-2018 Concrete Structures and the AS 1170 series structural design actions, including wind region B parameters for Sydney
- AS 1379-2007 concrete supply specification and AS/NZS 4671 reinforcing steel grades
- National Construction Code 2022 and NSW development approval requirements
- Timoshenko & Woinowsky-Krieger, Theory of Plates and Shells (1959)
- Billington, Thin Shell Concrete Structures (1982)
- Q4 2025 Sydney metropolitan construction rates
Limitations
The design sits at rough-order-of-magnitude level with ±30% cost accuracy, and the membrane analysis assumes no edge disturbances. Foundation design remains preliminary, resting on an assumed bearing capacity of at least 200 kPa that a geotechnical investigation would still need to confirm.
Figures from this analysis
How this research was produced
K-Dense Web planned and ran this engineering investigation end to end — gathering the sources, carrying out the analysis, producing the figures, and drafting the report. The full session transcript, including every intermediate step, is available to view.
