Freestanding masonry wall
A garden wall or fence: a concrete masonry stem cantilevered from a continuous concrete footing, under wind or a seismic coefficient. The stem is designed at the top of the footing to TMS 402-22 (reinforced or unreinforced, strength or allowable stress, with the switch in the toolbar); the footing is checked for overturning, sliding and soil bearing. US and metric units.
Edition. TMS 402-22 is not on hand: the stem uses the shared masonry library (the 402-13 text with the 402-22 numbering where confirmed, as the other masonry types). The wind on a freestanding wall follows ASCE 7-22 29.3; whether 7-22 writes Kd inside Eq. 29.3-1 is to be confirmed. CMHA TEK 14-16B, Concrete Masonry Fence Design, is on hand and its tables are compared below.
Inputs of the freestanding wall #
- Wall: exposed height above grade; the stem below grade to the top of the footing (TEK 14-16B uses 18 in. for 4 and 6 ft fences, 24 in. for 8 ft; check frost depth); thickness; reinforced or unreinforced; grouting (fully, or only the cells with bars); f′m; for unreinforced stems the mortar; for reinforced stems the bar, its spacing and grade (bars at the centre of the wall); the wall weight with its grout.
- Wind: a strength level pressure entered, or computed from the basic wind speed, exposure, Kzt, Ke, Kd (0.85 for solid freestanding walls) and the force coefficient Cf of ASCE 7-22 Figure 29.3-1, which you read for the wall's proportions: 1.3 for a long wall with clearance ratio s/h = 1 (case A), up to 1.8 for short walls, and higher near free ends (case C). Kz is taken at the top of the wall, at least 15 ft.
- Seismic: a horizontal coefficient on the stem's weight at strength level, from ASCE 7-22 Chapter 15 for the structure; 0 for none.
- Footing and soil: width, thickness and the stem's offset from its centre (both wind directions are checked); concrete and soil unit weights; the allowable bearing pressure (geotechnical report or IBC Table 1806.2); the friction coefficient; whether to count the lateral bearing pressure of IBC 1806.2 down to the footing bottom; the factors of safety for overturning and sliding. IBC 1807.2.3 asks 1.5 for retaining walls; for a fence it is your choice, 1.5 prefilled.
Auto-design (editor toolbar) varies the wall thickness, the bar and spacing and the footing width. Objective: the least masonry, steel and footing concrete. The wall weight is an input and is kept.
Checks performed #
| Check | Basis |
|---|---|
| Stem flexure, reinforced | Strength: 0.80 f′m stress block (face shell, or face shell and grouted cells), φ from the net tensile strain (TMS 402-22 9.3.2, Table 9.1.4). Allowable stress: cracked transformed section (8.3) |
| Stem flexure, unreinforced | Net tension M/S − P/A at most φ fr (Table 9.1.9.1, φ = 0.60) or the allowable tension of Table 8.2.4.2 |
| Stem shear | 9.3.3.1.2 or 8.3.5 (reinforced, γg = 0.75 when partially grouted); 9.2.6 or 8.2.6 on the webs (unreinforced) |
| Overturning | Unfactored dead load (stem, footing, soil on the footing) about the toe against the lateral load at 0.6W or 0.7E |
| Sliding | Friction μ N plus the optional lateral bearing, against the lateral load at 0.6W or 0.7E |
| Soil bearing | Every ASD combination of ASCE 7-22 2.4, no tension between footing and soil |
The stem is checked at the top of the footing, where the moment is largest. The drawing is the wall section with the stem bar, the footing and grade.
Limitations #
- One foot of a straight cantilevered wall. Pier-and-panel fences, pilasters, serpentine walls (TEK 14-16B Figure 2) and walls between returns are not covered.
- Free ends without a return carry more wind: TEK 14-16B adds 5 psf over a length equal to the height; Figure 29.3-1 case C gives higher coefficients. Enter the higher pressure for that length.
- The footing's own reinforcement, dowels and laps, the coping and control joints are not designed.
- Second-order effects in the stem are neglected (short cantilevers); the footing's own seismic inertia is not added.
Verification examples #
Verification status: 8 values compared in 3 examples (0 published, 3 hand calculations from the cited equations): 8 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: not yet recorded for this module.
No published calculation of a fence to the current codes is on hand: hand calculations of the wind pressure, the footing stability and bearing, and the stem strength. CMHA TEK 14-16B's Tables 2 and 4 are prescriptive selections (2003 / 2006 IBC, ASCE 7-05, f′m 1,500 psi) and are read backward in the behaviour tests: an 8 ft fence of 8 in. CMU with No. 4 bars at 24 in. under the table's 20 psf (32 psf at strength level) uses about 88 percent of its flexural strength here and fails at twice the spacing; the table's 12 by 42 in. footing passes overturning and bearing on 2,000 psf soil.