Take the section of the standard timber, the cai, as the module of the building: it is 15 fen high and 10 fen wide, and every member is dimensioned in fen.
1 cai = 15 fen (height) × 10 fen (width)
Rules · Columns · Structure · Optics
Cejiao: lean the columns inward
Set the heads of the outer columns inward: on the front and back by 1 fen for every chi of height (1/100), on the ends by 8 li per chi (8/1000); the corner columns lean both ways.
lean = 1/100 of height (front) · 8/1000 (flanks)
Leaning the whole perimeter inward makes the frame act a little like a truncated pyramid: the column heads, tied by the lintels and plates, press toward each other, and the frame resists racking in wind and earthquake. It also counteracts the impression that tall columns splay outward under a heavy roof. Korean builders call it anssollim.
Related rules
Between two stacked arms leave a spacer of 6 fen, the zhi; a cai plus a zhi, 21 fen, is a “full timber” (zucai) and the vertical step of each tier of a bracket set.
zucai = 15 + 6 = 21 fen
Build the bracket set (puzuo) of blocks (dou) and arms (gong) crossing at right angles, each tier projecting no more than 30 fen beyond the one below; a set of n projecting tiers is called an (n + 3)-puzuo, from four to eight.
projection per tier ≤ 30 fen · rise per tier = 21 fen · puzuo = tiers + 3
Where the eaves must project far, replace the outer arms by slanting levers (ang) that run down and out beyond the bracket set and rise inward to be held down under an interior purlin.
Shape the underside of every arm’s end in four or five facets, and reduce the upper third of a spindle column by the same method, so that no member ends in a hard corner.
From the intermediate bracket set of the second bay the rafter ends advance progressively outward, so that at the corner the eave projects further (by 4 cun for a hall of one bay, 5 for three bays, 7 for five bays) and rises with the corner beam.
Cite this page Chris Paton, “Cejiao: lean the columns inward”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/cejiao. Text, drawings and models licensed under CC BY-NC 4.0.