Masonry Magazine April 1966 Page. 26
FIGURE 1
Vertical rods in filled cells, see table below for size and spacing.
design
The main forces acting on a retaining wall are the pressures exerted by the earth it retains. These pressures are both horizontal and vertical in direction. Vertical pressure is the weight of the soil.
See table below for height (h) of wall.
See table below for distance (a) to exposed face of wall.
See table below for thickness (t) of footing.
Use key when wall height is 6 ft. or more.
See table below for width of footing.
Two-in, bars in bond beams at 16-in. o.c. OR Joint reinforcement at 8-in. o.c.
Metal lath may be placed over cells not containing reinforcement to prevent filling with grout.
Provide clean-out openings at dowel locations.
Size and spacing of horizontal rods in footing, see table below.
Longitudinal rods in footing %-in, at 12-in. o.c.
Designs herein are based upon an assumed soil weight of 100 pounds per cubic foot. Horizontal pressure is based upon an equivalent fluid weight for the soil. Equivalent fluid weight used is these designs is 45 pounds per cubic foot. This equivalent fluid weight is considered satisfactory for most purposes.
The horizontal pressure exerted by the retained earth can cause:
1. the retaining wall to break at the junction of the wall and its footing
2. overturning of the wall and footing intact, and
3. horizontal sliding of the wall and footing.
Walls shown herein were designed with safety factor against overturning of not less than 2, and a safety factor against horizontal sliding of not less than 1.5. Reinforced concrete footing designs are based upon the "ACI Building Code Requirements for Reinforced Concrete, (ACI 318-63), and the masonry wall designs are based upon the "ASA Building Code Requirements for Reinforced Masonry," (ASA 41.2-1960).
In computing the allowable wall height (h) shown in Table III, it was assumed that the backfill has a level, horizontal surface. Walls supporting a sloping soil surface, or walls subjected to surface loads, such as roadways, buildings, etc. should be designed to resist these additional forces. One method of providing for additional loads is to consider them as an additional depth of soil. Thus, an extra load of 300 pounds per square foot can be treated as an additional three foot of depth of soil weighing 100 pounds per cubic foot.
More detailed information on such items as sloping backfill, design procedures and tests on retaining walls is contained in NCMA Publication TR 49, "Reinforced Concrete Masonry Retaining Walls."
TABLE III-REINFORCED CONCRETE MASONRY RETAINING WALLS
8" WALLS
| Height of Wall-h | Width of Footing | Thickness of Footing-t | Dist. "a" to Face of Wall | Size & Spacing of Vertcal Rods in Wall | Size & Spacing of Horizontal Rods in Footing |
|---|---|---|---|---|---|
| 3'-4" | 2-4" | 9" | 8" | %" @ 32" | %" @ 27" |
| 4-0 | 2-9 | 9" | 10" | %" @ 32" | %" @ 27" |
| 4'-8" | 3'-3" | 10" | 12" | % @ 32° | @ 27" |
| 5′-4" | 3-8 | 10" | 14" | ½" @ 16" | ½" @ 30 |
| 6-0 | 4-2" | 12" | 15" | %*@24" | @25" |
12" WALLS
| | | | | | |
|---|---|---|---|---|---|
| 6'-8" | 4-6 | 12 | 16" | % @ 24" | % @ 22" |
| 7-4" | 4'-10" | 12" | 18" | %@32" | %@ 26" |
| 8-0 | 5-4" | 12" | 20 | @24" | %"@21" |
| 8′-8" | 5'-10" | 14" | 22 | %@ 16" | %" @ 26" |
| 9-4" | 6-4 | 14" | 24 | 1*@8" | **@ 21" |