Problem
If you conceive and build a room by first placing columns at the corners, and then gradually weaving the walls and ceiling round them, the room needs a perimeter beam around its upper edge.
Solution
Build a continuous perimeter beam around the room, strong enough to resist the horizontal thrust of the vault above, to spread the loads from upper stories onto columns, to tie the columns together, and to function as a lintel over openings in the wall. Make this beam continuous with columns, walls, and floor above, and columns and walls below.
Related Patterns
… this pattern helps to complete Box Columns (216), by tying the tops of the columns together once they are in position. It also helps to form the bearing surface for the edge of the Floor-Ceiling Vaults (219). For this reason, the positions of the perimeter beams must correspond exactly to the edges of the vaults laid out in Floor and Ceiling Layout (210).
Remember to place reinforcing in such a way that the perimeter beam acts in a horizontal direction as well as vertical. When it forms the base for a Floor-Ceiling Vaults (219) it must be able to act as a ring beam to resist all those residual horizontal outward thrusts not contained by the vault. Strengthen the connection between the columns and the perimeter beam with diagonal braces where the columns are free standing Column Connections (227) …
Reference for full-text of Pattern: p. 1018medium-confidence