When should ladder-type joint reinforcement be used and when should truss-type joint reinforcement be used?

ANSWER: 

Although the Specification for Masonry Structures, TMS 602-11/ACI 530.1-11/ASCE 6-11, does not provide guidance on which type of joint reinforcement to use, the Building Code Requirements for Masonry Structures, TMS 402-11/ACI 530-11/ASCE 5-11, prohibits using truss-type joint reinforcement to connect the wythes in non-composite masonry walls (multi-wythe walls with a non-mortared and non-grouted collar joint).    While ladder-type joint reinforcement can be used anywhere, there is another condition under which truss-type joint reinforcement should not be used.

The diagonal cross wires of truss-type joint reinforcement will interfere with placement of vertical reinforcing bars relative to the tolerances of the Specification for Masonry Structures and can inhibit grout flow.  Therefore, truss-type joint reinforcement should not be used in vertically reinforced single or multi-wythe masonry walls.  Ladder-type joint reinforcement may be used, but the cross-rods should be specified to be spaced at 16 inches on center. Some manufacturers produce joint reinforcement with cross-wires at a non-modular spacing, which can also interfere with placement of grout and vertical reinforcement.

The only type of construction in which truss-type joint reinforcement is preferred is in single wythe concrete masonry that is not vertically reinforced.  The truss-type joint reinforcement is stronger than ladder-type in axial tension and better able to resist the tensile stresses that develop from shrinkage of the concrete masonry.

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