NASCLA Accredited Commercial General ContractorMasonryMedium
A masonry crew is installing a reinforced concrete masonry unit (CMU) wall. What is the primary purpose of placing horizontal joint reinforcement (ladder or truss type) in a CMU wall?
- ATo provide primary resistance against compressive loads.
- BTo serve as anchors for veneer attachment systems.
- CTo increase the wall's resistance to flexural stresses and control cracking.
- DTo facilitate the drainage of moisture within the wall cavity.
Show answer & explanationAnswer & explanation
Correct answer: C. To increase the wall's resistance to flexural stresses and control cracking.
Horizontal joint reinforcement, such as ladder or truss type, is primarily used to increase the flexural strength of a masonry wall, making it more resistant to bending forces, and to distribute shrinkage stresses, thereby controlling cracking.
Why the other options are wrong
- A. Vertical rebar and the CMU units themselves primarily resist compressive loads.
- B. While some types can incorporate ties, their primary purpose is not veneer anchoring.
- D. Drainage is handled by weep holes, flashing, and cavity design, not by horizontal joint reinforcement.
Horizontal Joint Reinforcement
Steel wires embedded in mortar joints of masonry walls, typically ladder or truss type, to improve flexural strength and control cracking.
- Resists bending forces (flexural stresses).
- Distributes shrinkage stresses.
- Helps control thermal expansion/contraction.
- Placed at specified vertical intervals.
Memory trick: Horizontal wires are the 'belt' for bending and cracks.