SlendernessSr = lesser of Eq. (1) & (2) when vertical edges supported and Fd ≤ 0.20Fo (Cl. 7.3.4.3a). Otherwise Eq. (1) only: Sr = αvH / (kt·t). Limit: Sr ≤ 35.
αhHorizontal slenderness coefficient: 1.0 for lateral support on both vertical edges; 2.5 for support on one vertical edge only (Fig. 7.2).
ktEquivalent thickness factor from Table 7.2. = 1.0 for plain walls without piers. For walls with engaged piers, kt > 1.0 — use Table 7.2.
Ab hollowFor hollow (face-shell bedded) units, Ab = 2 × tfs × length (Cl. 4.5.4b). Webs not included. Typical tfs: 90 mm→25 mm, 110 mm→28 mm, 140 mm→30 mm, 190 mm→32 mm, 240 mm→38 mm.
Ag groutAg = Ad − Ab (Cl. 4.5.7). For fully grouted hollow wall: Ag = gross section minus face shells = core void area.
αv = 0.75Both ends rotationally restrained — e.g. wall between two RC slabs.
αv = 0.85Top pinned, bottom fixed (most common — roof bearing on wall).
αv = 1.0Both ends pinned — laterally supported but no rotational restraint.
αv = 2.5Cantilever — base fixed, top free. High slenderness penalty.
Wall height Hw
mm
Wall length L
mm
Nominal block size
Block dimensions assumed—
Wall thickness twoverride
mm
Unit height huoverride
mm
Face shell tfsoverride
mm
Support conditions (αv)
Vertical edge support (αh) Cl. 7.3.4.3
Equivalent thickness factor ktTable 7.2
Custom kt value
—
—mm
Eq. 7.3.4.3(1) — vertical slenderness—
—
Eq. 7.3.4.3(2) — two-way slenderness—
—
Sr = lesser of above ≤ 35
Governing value — AS 3700 Cl. 7.3.4.3
—/ 35
—
—
Ab — bedded area (face shells only, Cl. 4.5.4b)
—
—mm²/m
Ag — grout area = Ad − Ab (Cl. 4.5.7)
—
—mm²/m
BBlock & mortar propertiesCl. 3.2 · 3.3 · 11.4
Masonry unit type
Unit & bedding type — AS 3700:2018 Table 3.1
Face-shellHollow concrete blocks: mortar applied to face shells only. Ab = 2×tfs×length (Cl. 4.5.4b). Standard for blockwork per Cl. 12.4.2.
Fully beddedMortar applied across full cross-section. Used for solid, cored and calcium silicate units.
Mortar classM3 or M4 required for reinforced masonry (Cl. 11.4.5). M2 not permitted. The unit type selection includes the mortar class for clay units.
Mortar class
Unit strength f′uc
f′mb — masonry strength (Table 3.1 × kh)
—MPa
Mortar joint thickness tjfor kh, Table 3.2
mm
kh (Table 3.2) · hu/tj ratio
—
Flexural tensile strength f′mt
MPa
f′mt — flexural tensile strength — Cl. 3.3.3
0.20 MPaDefault value for clay, concrete and calcium silicate masonry at mortar joints. May be used without testing.
ZeroMust be taken as zero for sustained loads (not transient). Live loads are not transient. Use 0.20 MPa for wind and earthquake only.
Up to 1.0 MPaFor special masonry confirmed by prism tests during construction (Cl. 3.3.3).
0.15 MPaCharacteristic value for clay, concrete and calcium silicate masonry at mortar bed joints (Table 3.3 kv = 0.3).
UseContributes to in-plane shear capacity via Cl. 7.5.4 and Cl. 8.8. Also contributes to Vum in reinforced shear wall calculations.
CGrout propertiesCl. 3.5 · 11.7
Grout strength and fill extent
Grout — AS 3700:2018 Cl. 3.5 & 11.7
High-slump concrete (min 200 mm slump), ≥ 300 kg/m³ Portland cement, max 12 mm aggregate. Sample every pour — 100×200 mm cylinders at 28 days.
Min. f′cg12 MPa minimum (Cl. 11.7.3). Must be ≥ f′cm. Typically specified at 20–32 MPa.
Max. f′cg50 MPa maximum for design (Cl. 3.5 commentary — research basis only extends to 50 MPa).
Full fillAll cores grouted. Gross section used for Ab. Grout term: kc·(f′cg/1.3)(0.55+0.005·f′cg)·Ag.
kc factorStrength factor for grout in compression — AS 3700:2018 Cl. 8.5.1. kc = 1.4 for hollow concrete masonry units with density > 2000 kg/m³ kc = 1.2 for all other masonry
Bond beamUse H-block or Double-U profile so grout fully surrounds horizontal bars. Standard closed-end blocks are not suitable.
As,h — horizontal steel per metre height
—mm²/m
Shear wall classification
—
FLoad eccentricityCl. 7.3.4.4
Bearing condition — tap to choose
Single span one side
Continuous equal loads
Continuous unequal loads
Custom enter mm
Bearing length tbear
Custom bearing length
mm
Bearing length used
—mm
Bearing length tbear — Cl. 7.3.4.4
The bearing length is the actual contact length of the floor or beam on the wall top. Load resultant acts at tbear/3 from the loaded face. Eccentricity from wall centreline: e = tw/2 − tbear/3.
75 mmMinimum practical bearing for timber joists, light steel sections, or thin slabs. Gives largest eccentricity — most conservative.
100 mmTypical minimum for concrete slab on blockwork. Common default in practice.
tw/2Half wall thickness — e.g. for 190 mm wall = 95 mm. Gives e = tw/2 − tw/6 = tw/3. A common conservative assumption.
twFull wall thickness bearing. e = tw/2 − tw/3 = tw/6. Aligns with the old simplified rule often quoted in practice.
CustomEnter the actual bearing length from your structural detail. Must reflect the real support geometry.
Floor load left side NL
kN/m
Floor load right side NR
kN/m
Custom eccentricity e1from wall CL
mm
Calculated eccentricity e1
—mm
e1 / tw ratio
—
GApplied loads — ULS per metre runAS 1170 · Cl. 2.5
Per metre runInclude factored self-weight (~3.5–5 kN/m² for 190 mm grouted blockwork ≈ 10–15 kN/m for 3 m wall) plus factored floor/roof loads.
Load combos1.2G+1.5Q · 1.2G+ψcQ+Wu · 0.9G+Wu (critical for low axial + lateral). Per AS 1170.0.
Design OOP moment M*
kNm/m
M* — ULS out-of-plane bending moment — Cl. 2.5
From windp × H²/8 for pin-pin, p × H²/12 for fixed-fixed. Example: p=1.0 kPa, H=3 m, pin-pin → M*=1.13 kNm/m.
Per metre runMoment in the vertical bending plane (spanning between horizontal supports top and bottom).
Design in-plane shear V*
kN/m
V* — ULS in-plane shear — Cl. 2.5
Per metre runHorizontal in-plane shear from diaphragm forces distributed to shear walls based on tributary area and relative stiffness.
Governing clauseH/L < 2.3: Cl. 8.7.2 long wall. H/L ≥ 2.3: Cl. 8.8 short wall. No horizontal reo: Cl. 7.5.4 unreinforced only.
Capacity results
HCompressive capacity φFoCl. 8.5.1
AS 3700:2018 Eq. 8.5.1 — Full equation
where φ = 0.75 (Table 4.1) · kes = slenderness & eccentricity factor · Ab = gross bedded area · Ag = grout area · αr = 0.4 (grout annulus restraint, single leaf)
—
—kN/m
kc·(f′cg/1.3)(0.55+0.005·f′cg) — power grout term, Cl. 8.5.1 (kc = 1.3)—