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Roman Pantheon Hemispherical Coffered Dome & Rotunda
Structural simulation of the 43.3 m unreinforced pozzolanic concrete dome with 9.0 m compression oculus ring, cylindrical rotunda drum, stepped buttresses, and 12-column portico.
The Pantheon in Rome remains the world's largest unreinforced concrete dome after nearly two millennia. Its structural ingenuity relies on a pure hemispherical profile (internal diameter 43.3 m, matching its internal height), a 9.0 m open compression oculus ring at the summit, seven external stepped annular buttress rings, and a 6.0 m thick cylindrical rotunda wall. This model captures the rotunda cylinder, dome shell, coffered meridian/parallel ribs, and the 12-column entrance portico. WebCAE evaluates hoop tension cracking tendencies, radial thrust transfer into the drum, and dome stability under gravity.
1. Geometry & FEA Mesh
- •Geometry: hemispherical dome Ø 43.3 m, apex elevation 43.3 m, central oculus Ø 9.0 m, rotunda drum H = 21.65 m, entrance portico 16 × 12 m with 12 columns H = 14 m.
- •Shell & coffer framing: 480 MITC4 shell quad elements representing the tapered dome shell (t = 1.2 m at base to 0.4 m at oculus) and drum walls, stiffened by 712 coffered beam ribs.
- •Oculus & stepped rings: reinforced circular compression ring around the oculus resisting hoop thrust, coupled to 7 external stepped ring beams at the dome haunch.
- •Discretization: 546 nodes, 712 beam members, 480 shell quads, 3,012 DOFs with validated connectivity across all drum and dome intersections.
2. Loads & Boundary Conditions
- •Fixed base support restraints (all 6 DOFs) along the circular foundation perimeter of the rotunda wall and portico column bases (z = 0).
- •Gravitational self-weight (pozzolanic concrete E = 25 GPa, ν = 0.20, density 2,200 kg/m³ in drum, tapering density towards apex).
- •Radial seismic and horizontal live loads simulating vault thrust distribution into perimeter masonry.
3. Simulation Results & Findings
- ✓Maximum vertical static deflection |u| = 88.1 mm at the inner rim of the compression oculus ring under full dead load.
- ✓Fundamental mode frequency f₁ = 2.00 Hz corresponds to coupled lateral sway of the entrance portico colonnade and dome ovalization.
- ✓Eigenvalue buckling load factor λ₁ = 58.3 confirms immense reserve against global axisymmetric dome snap-through.
WebCAE offers heritage conservation specialists and structural engineers an accessible platform to model monumental unreinforced masonry and concrete domes, evaluating hoop stresses, oculus ring compression, and seismic resilience.
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