aLOTofImaginArches

Interactive line of thrust and funicular analysis of masonry arches — user guide

Example

Trace your own

Load an image Image width Image height locked Distance

Click along a curve; double-click, or press Enter, to finish. Esc cancels.

Blocks Unit weight kN/m³ Thickness m

Circular ring

An exact ring from its numbers, with no image to trace. The published figures for the admissible band and the least admissible thickness are computed on this ring, so a point of either can be checked here by hand.

Inner radius Thickness ratio t/r_i Blocks

uses the unit weight and thickness above

3-point circular arch

pick 3 intrados and 3 extrados points

Trace a whole profile

For a section the two faces cannot describe: a filled haunch, a widening pier, or the two shells of a dome. Trace each closed outline in turn; the joints come from rays out of a picked centre, so every shell is cut at the same angles.

Blocks

no outline traced

Add a block

Sides

Click the corners in turn. Useful for a pier, a fill, or anywhere the radial cut does not suit the shape.

Scale

not scaled — lengths are pixels

Dome slice — Poleni

Treat the arch as a dome lune

A barrel vault cut into voussoirs gives blocks of constant width. A dome cut into lunes does not: each is bounded by two meridian planes, so it is broad at the major parallel and closes to nothing at the crown. The weights follow, and so does the line of thrust — this is what Poleni saw in 1748.

Slice angle ° Axis x

off — constant thickness

Save and reopen

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Writes everything — the traced curves, the blocks, the applied forces, the scale, the background image and the equilibrium state — to one JSON file.