Joint Reinforcement in Stack Bond Masonry Omaha NE

Why do codes require the reinforcing of stack bond masonry with horizontal joint reinforcement in Omaha? I understand that stack bond masonry does not have overlapping units as in a running bond pattern.

Meier Masonry Inc
(402) 493-3345
1808 N 138th St
Omaha, NE
 
DC Masonry Inc
(402) 896-8324
4908 S 61st St
Omaha, NE
 
AAA Chimney Sweep
(402) 330-6200
5088 S 106th St
Omaha, NE
 
Radil Robert E Tile Contr
(402) 571-4789
9823 Laurel Ave
Omaha, NE
 
Pool Steven
(402) 496-4776
14010 Camden Ave
Omaha, NE
 
K & K Masonary
(402) 895-7963
4905 S 66th Plz
Omaha, NE
 
Cole Brother's Masonry Inc
(402) 932-3043
13301 Cooper St
Omaha, NE
 
Thompson Masonry
(402) 689-0831
Omaha, NE
 
Top Hat Industries Inc
(402) 496-4776
Omaha, NE
 
Seedroff Masonry Inc
(402) 895-4604
14711 Custer Rd
Omaha, NE
 

Joint Reinforcement in Stack Bond Masonry

Provided By:

Source: MASONRY CONSTRUCTION MAGAZINE
Publication date: October 1, 1998

Why do codes require the reinforcing of stack bond masonry with horizontal joint reinforcement? I understand that stack bond masonry does not have overlapping units as in a running bond pattern. This overlapping, however, does not occur across bed joints in any masonry walls, yet the codes do not require vertical reinforcement.
The purpose of horizontal joint reinforcement in stack bond masonry is to limit vertical cracking. The overlapping units in running bond masonry will provide more strength across vertical planes because they eliminate the continuous vertical joints that occur in stack bond walls. There is very little mortar-to-brick bond strength at head joints. Running bond patterns do not depend on the head joints for strength in a horizontal direction but rather on the strength of the units themselves.The reason head joints typically have lower bond strengths than bed joints is related to the orientation of the mortar joint when the walls are constructed. In running bond masonry, the horizontal mortar joint is easy to place with full joints. Also, the bed joints are under compression when the wall is laid up due to the masonry's weight. Head joints are formed by buttering the end of the units with mortar and shoving them into the adjacent units. Unlike bed joints, they are not under compression.

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