Page 331 - Masonry and Concrete

Masonry Garden Walls

330 CHAPTER NINE

Recommended Spacing Vertical Spacing of Joint Reinforcing
of Control Joints None 24 inch 16 inch 8 inch
1
Expressed as ratio of panel 2 2 ⁄2 3 4
length to panel height, L/H
With panel length (L) not 40 45 50 60
to exceed, feet

FIGURE 9-19

CMU control joint spacing. (from NCMA, TEK 10-1, National Concrete Masonry Associa-
tion, Herndon, VA).

The height of freestanding CMU garden walls is limited by the same
height-to-thickness (h/t) ratio as brick walls. Maximum wall height
should not exceed 18 times the wall thickness. An 8-in. wall can be a
maximum of 12 ft. high. Lateral support must be provided at the same
ratio of 18 times the thickness of the wall (Figure 9-3). This means that
an 8-in.-thick wall would require pilaster stiffening every 12 ft. With
hollow CMU walls, vertical reinforcing steel can be grouted into the
cores of the units, which essentially creates an integral pilasters where
the wall thickness remains the same (Figure 9-21c). Alternatively, pro-
jecting pilasters may be created with standard units bonded into the
wall (Figure 9-21b) or with special pilaster units (Figure 9-21a). Pro-
jecting pilasters may be hollow, grouted, or grouted and reinforced,
depending on the lateral loads and the height of the wall. In seismic
areas and coastal areas subject to hurricane winds, grout and reinforc-
ing steel will be required to meet code requirements for load resistance.
Ungrouted hollow pilasters should project from the wall a distance
1
equal to approximately 12 of the wall height, and their width should
1
be equal to approximately 10 of the horizontal span between supports.
Using either standard or special units based on the 8 16 module will
produce an 8-in. projection with a 16-in. width, which is adequate for
wall heights of up to 8 ft. and pilaster spacings of up to 12 ft.
The course of block just below the coping in a CMU wall should be
filled solidly with grout. Lay pieces of screen wire in the bed joint
below this course so the grout will not flow down into the rest of the
wall. Cap the wall with flat coping block or stone and install flashing
in the same way as for brick walls (Figure 9-22).

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