A round barn is not a frame, it is a solid of revolution, and two facts follow that a plane-frame tool gets wrong: a rafter's tributary wedge grows with radius (so its load is triangular, never uniform), and the plates are RINGS — the plate works in tension, the curb at the peak in compression, and that hoop is the whole reason a round barn's mow has no post in it. Rotunda models one radial rib — the section Wilber Fraser drew for the Illinois experiment station in 1910 — and solves it with Armature's own FE engine, then adds the axisymmetry: wedge loading, ring stiffness as a real elastic restraint, and a switch that lets the sprung roof boards work as a hoop so you can watch the load path change from basket to shell. The barn it opens on is the one Fraser describes, not just the one he drew: a 9-foot brick cow storey under 20-foot studs with the plate 29 feet up, 64 framed rafters doubled below the break because that is where the wedge is wide, mow joists on a post ring at the stanchions, and the silo running through the peak as a mast. Set it on sliders, lay out his rings from silo to litter alley and read the cows off the stanchion circle — dimensioned at both ends, because a stall in a circle is a wedge — then size every stick and price the result in his own 1910 money against the $799.76 he billed.
Runs entirely in your browser — nothing is uploaded. What it shares with professional analysis: a genuine first-order plane-frame solve on real dressed lumber, with axisymmetric loads and ring mechanics that are exact within the model, and compression checked over whole members rather than the segments they are solved in. What it does not have: wind on the structure (the one load that is not axisymmetric — the readout answers Fraser's windstorm claim as a global drag comparison instead), buckling of a compression ring out of round, splice and connection design, γ-factors and code load combinations, and a licensed engineer who signs it. The 1910 bill counts only the members the model solves, so it reads light against Fraser's own, and says so. Exports the ring schedule and takeoff as CSV, and the whole revolved barn as an OBJ for Rhino.