Q: We are planning to place a slab on grade containing welded wire fabric. Should the fabric be continuous through sawed contraction joints?

A: There's no general agreement on this question.

Concrete Floors on Ground, published by the Portland Cement Association, recommends discontinuing distributed-steel reinforcement at contraction joints. ACI 301-99, "Specifications for Structural Concrete," directs contractors not to extend welded wire fabric through contraction joints unless otherwise permitted. Some designers, though, believe that allowing some of the wires to pass through the concrete aids load transfer through aggregate interlock. They often require cutting every other wire at contraction joints.

Ringo and Anderson (see reference) say that a small percentage of welded wire fabric sheets may be continuous through contraction joints. However, it must not be enough to inhibit the function of the joint.

ACI 350R-89, "Environmental Engineering Concrete Structures," refers to full and partial contraction joints. In full contraction joints, all reinforcement is terminated 2 inches clear of the joint. In partial contraction joints, not more than 50% of the reinforcement is passed through the joint. This is done to weaken the joint and ensure crack formation while still passing tension forces through the joint to tie portions of the structure together.


 Boyd C. Ringo and Robert B. Anderson,

Designing Floor Slabs on Grade, Second Edition, The Aberdeen Group, Addison, Ill., 1996, p. 177.