jack — a mechanical device used for applying force to prestressing tendons, for adjusting elevation of forms or form supports, and for raising objects small distances.
jack, flat — a hydraulic jack consisting of light gage metal that is folded and welded to a flat shape that expands under internal pressure.
jack shore — telescoping, or otherwise adjustable, single-post metal shore.
jacking device — the device used to stress the tendons for prestressed concrete; also the device for raising a vertical slipform.
jacking force — see force, jacking.
jacking stress — see stress, jacking.
jaw crusher — a machine having two inclined jaws, one or both being actuated by a reciprocating motion so that the charge is repeatedly nipped between the jaws.
jet, air-water — a high-velocity jet of air and water mixed at the nozzle, used in clean-up of surfaces of rock or concrete, such as horizontal construction joints.
jitterbug — a grate tamper for pushing coarse aggregate slightly below the surface of a slab to facilitate finishing. (See also tamper.)
1. a physical separation in a concrete system, whether precast or cast-in-place, including cracks if intentionally made to occur at specified locations; or
2. the region where structural members intersect. History
joint, butt — a plain square joint between two members.
joint, cold — a joint or discontinuity resulting from a delay in placement of sufficient duration to preclude intermingling and bonding of the material, or where mortar or plaster rejoin or meet. History
joint, construction — the surface where two successive placements of concrete meet, across which it may be desirable to achieve bond and through which reinforcement may be continuous.
joint, contraction — formed, sawed, or tooled groove in a concrete structure to create a weakened plane to regulate the location of cracking resulting from the dimensional change of different parts of the structure. (See also joint, isolation; joint, expansion; and joint, construction.)
joint, control — see joint, contraction (preferred term).
joint, cross — the joint at the end of individual formboards between subpurlins.
joint, expansion — (1) a separation provided between adjoining parts of a structure to allow movement where expansion is likely to exceed contraction; or
(2) a separation between pavement slabs on grade, filled with a compressible filler material; or
(3) an isolation joint intended to allow independent movement between adjoining parts.
joint, flexible — see joint, hinge; hinge, Mesnager, and joint, semiflexible.
joint, groove — see joint, contraction (preferred term).
joint, hinge — any joint which permits rotation with no appreciable moment developed in the members at the joint. (See also hinge, Mesnager, and joint, semiflexible.)
joint, isolation — a separation between adjoining parts of a structure that allows relative movement in three directions. Isolation joints are usually vertical planes located to avoid formation of cracks in the structure. (See also joint, contraction and joint, expansion.) History
joint, lift — surface at which two successive lifts meet.
joint, longitudinal — a joint parallel to the length of a structure or pavement.
joint, raked — a masonry-wall joint that was the mortar raked out to a specified depth while it is only slightly hardened.
joint, sawed — a joint cut in hardened concrete, generally not to the full depth of the member, by means of special equipment.
joint, scarf — see connection, scarf.
joint, semiflexible — a connection in which the reinforcement is arranged to permit some rotation of the joint. (See also joint, hinge and hinge, Mesnager.)
joint, separation — see joint, isolation (preferred term).
joint, transverse — a joint normal to the longitudinal dimension of a structural element, assembly of elements, slab, or structure.
joint, warping — a joint with the sole function of permitting warping of pavement slabs when moisture and temperature differentials occur between the top and bottom of the slabs, that is, longitudinal or transverse joints with bonded steel or tie bars passing through them.
joint, weakened-plane — see joint, groove and joint, contraction (preferred term).
joint filler — see filler, joint.
joint sealant — see sealant, joint.
joint-sealing compound — see compound, joint-sealing.
joint spall — a spall adjacent to a joint.
jointed detail — see detail, jointed.
jointer (concrete) — a metal tool about 6 in. (150 mm) long and from 2 to 4-1/2 in. (50 to 100 mm) wide and having shallow, medium, or deep bits (cutting edges) ranging from 3/16 in. to 3/4 in. (5 to 20 mm) or deeper used to cut a joint partly through fresh concrete. (See also jointing.)
jointing — the process of producing joints in a concrete slab. [See also jointer (concrete).]
joist — a comparatively narrow beam, used in closely spaced arrangements to support floor or roof slabs (which require no reinforcement except that required for temperature and shrinkage stresses); also a horizontal structural member such as that which supports deck form sheathing. (See also beam.)
jumbo — traveling support for forms, commonly used in tunnel work.
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