A concrete block bearing wall designed to AS 3700 uses a capacity reduction factor approach that separates the material's basic compressive capacity from a slenderness-and-eccentricity-dependent reduction, similar in structure to several masonry codes covered elsewhere in this series but with its own specific k-factor formulation.
Every check above runs automatically inside the Structyze Masonry Bearing Wall module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
The Example We'll Use
- Wall: 190 mm hollow concrete block, fully grouted, storey height 2.8 m
- Unconfined compressive strength of masonry f'm: 12 MPa
- Design axial load: 115 kN/m run, eccentricity: 15 mm
Working Through It
Slenderness ratio S_r = k_h × H / t_h = 0.75 × 2800 / 190 = 11.1 (using AS 3700's effective height factor for this top and bottom restraint condition).
Capacity reduction factor k, combining this slenderness ratio with the e/t_h = 15/190 = 0.079 eccentricity ratio per AS 3700's design chart, gives k ≈ 0.82.
Design vertical capacity per metre run = φ × k × f'm × t_h × 1000 (thickness and the 1000 mm design strip both in mm) = 0.75 × 0.82 × 12 × 190 × 1000 × 10⁻³ = 1,402 kN/m run.
Utilization: 115 / 1402 = 0.08, reflecting that this particular wall is lightly loaded relative to its capacity — common for an upper-storey bearing wall carrying only roof and top-floor load.
What Governs, and Why
This wall clears its capacity with a very wide margin (utilization 0.08), which is a realistic outcome for an upper-level bearing wall rather than a sign the design was over-conservative — the same wall thickness and block grade, carried down to a ground-floor wall accumulating load from several storeys above, would show a meaningfully higher utilization against the same capacity formula.
Where Structyze Takes Over
Every check above runs automatically inside the Structyze Masonry Bearing Wall module — this particular module is part of the full desktop catalogue rather than the free browser trial, since the trial only carries a curated flagship set. You can still try the free trial modules right now to see the same calculation style in action on RCC Beam, Column, Slab and a handful of others.
For Masonry Bearing Wall and the rest of the full catalogue — 80+ components across RCC, Steel, Composite, Timber, Masonry and more, across 20+ design codes — buy the full Structyze desktop app or see everything it does on the Software page.
Quick FAQ
Why would an engineer still check a wall that so comfortably clears its capacity?
Because minimum thickness, fire rating, and constructability requirements often govern a wall's actual dimensions well before pure axial capacity does, particularly for upper-storey walls carrying light load — confirming the capacity check passes is still necessary even when it's clearly not the limiting consideration for that specific wall.
Does AS 3700's capacity reduction factor k use the same input variables as IS 1905's stress reduction factor discussed elsewhere in this series?
Conceptually yes — both combine slenderness and eccentricity into a single reduction factor applied to basic material capacity, though the specific numerical formulation and design chart differ between the two codes, reflecting each one's own calibration.
Final Thoughts
A wall with a very comfortable utilization isn't necessarily over-designed — it's often just telling you the governing constraint for that specific wall lies elsewhere (minimum thickness, fire rating, constructability) — the reason the capacity check still needs to be run and confirmed, not skipped just because the answer looks obviously fine.