joint, isolation — a separation between adjoining parts of a structure that allows relative movement in three directions; usually vertical planes located to avoid formation of cracks in the structure.   (See also joint, contraction and joint, expansion.)

Historical entry from ACI 116R-00, used prior to revision posted on February 7, 2008:

joint, isolation — a separation between adjoining parts of a concrete structure, usually a vertical plane, at a designed location such as to interfere least with performance of the structure, yet such as to allow relative movement in three directions and avoid formation of cracks elsewhere in the concrete and through which all or part of the bonded reinforcement is interrupted.  (See also joint, contraction and joint, expansion.)

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