AAC masonry wall

A one-foot strip of an autoclaved aerated concrete (AAC) masonry wall, spanning vertically between supports at the top and bottom, loaded out of plane with an axial load at the top: reinforced (TMS 402-22 11.3) or unreinforced (11.2), by strength design, the only method Chapter 11 offers. US and metric units.

Edition. TMS 402-22 is not on hand. Chapter 11 and Table 4.2.2 were read in TMS 402-16 (pp. C-32, C-161 to C-176). TMS's overview of the 2022 changes says the strength reduction factors moved into Table 11.1.5 with no other significant change; references give the 2016 section numbers, and steps that rest on them say "to confirm against the code text". The AAC strength classes and the strain factor α of the maximum reinforcement are from knowledge.

No free worked example of an AAC wall exists. This type was deferred in wave 7 for that reason and is now built on hand calculations only; see the verification section.

Inputs of the AAC wall #

• Wall: reinforced or unreinforced; specified thickness (AAC units are solid); height between the supports; a parapet above the top support (its weight only); wall weight.
• AAC: strength class AAC-2, AAC-4 or AAC-6 (f′AAC 290, 580 or 870 psi), or entered (at least 290 psi). Class 2 uses a maximum usable strain of 0.0012, class 4 and higher 0.003.
• Bed joint at the critical section: thin-bed mortar caps the modulus of rupture at 80 psi; a Type M or S leveling bed at 50 psi.
• Reinforcement: bar and spacing, centred in grouted cores; grade (design fy at most 60 ksi); grout strength (2,000 to 5,000 psi); core diameter (for the bar size and area limits); the strain factor α of the maximum reinforcement, 1.5 prefilled.
• Loads: w the axial load per foot at the top, e its eccentricity from the wall centre line, p the out-of-plane pressure.
• Limit shear to sliding friction μ Pu: on by default, Eq. 11-8 as written, with μ = 1.0 at a thin-bed or leveling bed. Dowels across the base joint (shear friction) are outside this calculation; turning the limit off is your decision.

Auto-design (editor toolbar) varies the thickness, bar size and spacing. Objective: the thinnest wall, then the least steel. The wall weight is kept, so a heavier wall gets no credit until you enter it.

Checks performed #

Material values: EAAC = 6500 f′AAC^0.6 (Table 4.2.2); fr = 2 × 2.4 √f′AAC capped by the bed (11.1.8.2, 11.1.8.3). The drawings are the wall section along its height and a plan section with the grouted cores.

Limitations #

• Out of plane, simply supported top and bottom (the 11.3.5.5.2 procedure). Cantilevers, partially supported walls and in-plane shear walls (11.3.6) are not covered.
• The bars are smeared over the foot of wall; the effective width of widely spaced bars (5.1.2) is not applied.
• Shear d is taken as t/2 for the unreinforced wall too, conservatively (to confirm against the code text).
• Bearing, anchor bolts in AAC, laps, bond beams and seismic detailing are not checked.

Verification examples #

Verification status: 13 values compared in 5 examples (0 published, 5 hand calculations from the cited equations): 13 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.

Hand calculations only. No free published AAC wall example exists: the Masonry Designers' Guide examples of Chapter 14 are paid. The hand calculations check the material values, a reinforced wall's moment, strength, stress block and shear, an unreinforced wall's tension, axial strength and slenderness, and the maximum reinforcement. This type should be read as hand verified until the Guide's examples are added.