Jack arch

Jack arch

A jack arch is a structural element in masonry construction that provides support at openings in the masonry. Alternate names are "flat arch" and "straight arch".

Unlike regular arches, jack arches are not semicircular in form. Instead, they are flat in profile and are used under the same circumstances as lintels. Unlike lintels, which are subject to bending stress, jack arches are composed of individual masonry elements cut or formed into a wedge shape that efficiently uses the compressive strength of the masonry in the same manner as a regular arch. Like regular arches, jack arches require a mass of masonry to either side to absorb the considerable lateral thrust created by the jack arch.

Jack arches have the advantage of being constructed from relatively small pieces of material that can be handled by individuals, as opposed to lintels which must necessarily be monolithic and which must be oversized unless reinforced by other means.

In small-scale brick masonry projects, jack arches are typically sawn from an appropriately-sized fired-clay lintel, giving a more precise and consistent joint width than field-sawn shapes.

There is considerable scope for incorporation of decorative patterns and elements into jack arches. Keystones, stepped or arched top profiles and polychrome or contrasting colors and materials may all be used to create the desired effect.

References

cite book
last = Beall
first = Christine
authorlink =
coauthors =
title = Masonry Design and Detailing (2nd Edition)
publisher = McGraw Hill Book Company
date = 1987
location =
pages =
url =
doi =
id =
isbn = 0-07-004223-3

cite book
last = Ramsey
first = Charles
authorlink =
coauthors = Sleeper, Harold
title = Architectural Graphics Standards (4th Edition)
publisher = John Wiley & Sons, Inc.
date = 1951
location =
pages =
url =
doi =
id =
isbn =


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  • Jack arch — Jack Jack (j[a^]k), n. [F. Jacques James, L. Jacobus, Gr. ?, Heb. Ya aq[=o]b Jacob; prop., seizing by the heel; hence, a supplanter. Cf. {Jacobite}, {Jockey}.] [1913 Webster] 1. A familiar nickname of, or substitute for, John. [1913 Webster] You… …   The Collaborative International Dictionary of English

  • jack arch — noun Etymology: jack (I) (something smaller) : a flat arch (as a lintel with a keystone) * * * Archit. See flat arch. [1880 85] * * * n. a small arch only one brick in thickness, esp. as used in numbers to support a floor …   Useful english dictionary

  • jack arch — Archit. See flat arch. [1880 85] * * * …   Universalium

  • Jack — (j[a^]k), n. [F. Jacques James, L. Jacobus, Gr. ?, Heb. Ya aq[=o]b Jacob; prop., seizing by the heel; hence, a supplanter. Cf. {Jacobite}, {Jockey}.] [1913 Webster] 1. A familiar nickname of, or substitute for, John. [1913 Webster] You are John… …   The Collaborative International Dictionary of English

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  • jack crosstree — Jack Jack (j[a^]k), n. [F. Jacques James, L. Jacobus, Gr. ?, Heb. Ya aq[=o]b Jacob; prop., seizing by the heel; hence, a supplanter. Cf. {Jacobite}, {Jockey}.] [1913 Webster] 1. A familiar nickname of, or substitute for, John. [1913 Webster] You… …   The Collaborative International Dictionary of English

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