Rules · Walls · Structure · Materials
In a thick wall, do not build two separate skins with loose filling between them: lay stones lengthwise into the thickness at intervals, and set single stones right through from face to face, so that the wall acts as one mass.
Vitruvius calls this Greek method emplekton (“woven in”). The through-stones (diatonoi) tie the two faces together, so that the wall cannot split into three parts: two thin facings and a core that settles away from them. He complains that Roman workmen, in their hurry, stand the facing stones upright and throw broken stones and mortar into the middle anyhow.
The principle that a header must cross the joint between leaves reappears in every masonry tradition: in the bonding courses of Roman brick-faced walls, in the “through-stones” of dry-stone field walls, and in the header courses of English brickwork.
A beam is squeezed along its top and stretched along its bottom; stone resists squeezing well but stretching badly, so a stone lintel must be deep in proportion to its span and cannot be long. Doubling the span quadruples the stress from its own weight.
σ ≈ ¾ ρ g L² ⁄ d (self-weight) · + ≈ 0.43 ρ g L³ ⁄ d² (a wall above)
In a bonded masonry wall the courses above an opening corbel over it of their own accord, so the lintel carries roughly the triangle of wall with sides rising at 60° from its ends; everything above that triangle arches onto the jambs.
load ≈ equilateral triangle on the span: W ≈ 0.43 · L² · t · ρ g
Weight for weight, timber is many times stronger in bending than stone; long spans in trabeated buildings are therefore roofed with timber beams resting on stone walls and columns.
bending strength ÷ density: oak ≈ 70 · limestone ≈ 3 (kPa per kg ⁄ m³)
Build an arch of wedge-shaped stones (voussoirs) whose joints all point towards the centre of the curve: each stone can then fall only by forcing its neighbours apart, and so the ring holds itself up once the last stone, the keystone, is in place.
joints ⟂ intrados (radial to the centre)
An arch pushes outward on its supports as well as down. For the same load and span the horizontal push grows as the rise falls: halve the rise and you roughly double the thrust.
H ≈ w·s² ⁄ 8f (uniform load w per metre, span s, rise f)
Trace the path of the resultant force through the stones from crown to foundations. If a line can be found that stays everywhere within the masonry, the arch will stand; where it touches an edge, a hinge will open, and four hinges make it collapse.
Cite this page Chris Paton, “Bind the faces with through-stones”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/emplekton-through-stones. Text, drawings and models licensed under CC BY-NC 4.0.