Masonry · Lintels, openings & bearing
Concentrated load on masonry with a padstone calculator
Beam reaction bearing on a masonry wall, first directly and then through a concrete padstone. The bearing factor kb grows with the ratio of the dispersed area at mid-height to the loaded area and with the distance to the wall end (solid units), and is 1 for hollow units. The padstone enlarges the loaded area, and the dispersed load plus the wall above is checked at mid-height.
Standard: AS 3700-2018 Cl 7.3.5 concentrated loads: Fd = φ·kb·f′m·Ab, kb = 0.55(1 + 0.5a1/L)/(Ab/Ade)^0.33 within 1 ≤ kb ≤ 1.5 + a1/2L (solid units) · 45° dispersion to mid-height
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Beam reaction (design) | 120 | kN |
| Beam bearing length | 150 | mm |
| Distance from the end of the wall to the bearing | 300 | mm |
| Wall thickness | 190 | mm |
| Wall length | 3000 | mm |
| Wall height | 2700 | mm |
| Unit strength f′uc | 20 | MPa |
| km | 1.4 | |
| Units | Solid / cored | |
| Padstone length | 440 | mm |
| Padstone depth | 150 | mm |
| Wall load from above (design) | 20 | kN/m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| f′m | 6.26 | MPa |
| Direct bearing: kb / φFd | 1.31 / 175.5 | / kN |
| With padstone: kb / φFd | 1.00 / 392.6 | / kN |
| Dispersed length at mid-height | 2,090 | mm |
| Load at mid-height / capacity (k = 0.67) | 161.8 / 1,249.3 | kN |
- ✓ Direct bearing adequate (padstone not needed) — 68 %
- ✓ Bearing on the padstone — 31 %
- ✓ Mid-height compression
Method, formulas and assumptions
- Fd = φ·kb·f′m·Ab, φ = 0.75. Solid units: kb = 0.55(1 + 0.5a1/L)/(Ab/Ade)^0.33, at least 1 and at most 1.5 + a1/(2L); hollow units kb = 1.
- Ade = t × dispersed length at mid-height (45° each side, limited by the wall end).
- Mid-height check uses the simplified compression capacity φ·k·f′m·A with k = 0.67 (stocky wall); use the wall tool for slenderness.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.