Knight's Mechanical Encyclopedia, J., Joist.

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19th-Century American

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Joist.

（Carpentry.) A horizontal timber supporting a floor or ceiling, one or both.

Floor-joists.

Single flooring is formed with joists reaching from wall to wall, where they rest on plates a of timber built into the brick-work. The floor-boards are nailed on the upper edges of the joists, whose lower edges receive the lathing and plastering of the ceilings. Double floors are constructed with stout binding joists b b, a few feet apart, reaching from wall to wall, and supporting ceiling joists c c which carry [1219] the ceiling, and bridging joists e e on which are nailed the floor boards.

When the main timbers of the floor are girders d which rest on the wall plates and support the binding joists b b, the floor is called a framed floor. The binding joists b b support the bridging joists e e and ceiling joists c c as before.

The trimming joists are short joists into which trimmers are mortised. Trimmers are pieces around a fire-hearth or a hatchway, where the continuity of the joists is broken.

The strength of joists, of equal thickness, is as the square of the height. A joist 4 × 6 has one quarter the strength of a joist 4 × 12. The latter is only twice as large.

Timber is weakened by sawing. A floor of 16 feet hearing, supported by 12 joists 8 inches square, 1 foot apart, is stronger than a similar floor of 24 joists, 8 × 4, placed edgeways, 6 inches apart. The quantity of timber is the same in both cases.

1877.

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Knight's Mechanical Encyclopedia
Knight, Ed.

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Joist.

Knight's Mechanical Encyclopedia Knight, Ed.

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Table of Contents:

Joist.

Knight's Mechanical Encyclopedia
Knight, Ed.