Masonry · Lintels, openings & bearing
Masonry lintel loading with arching calculator
If enough masonry stands above the opening the lintel carries only a 45° triangle of masonry; otherwise the full height of masonry and any floor load. Gives M*, V* and the section modulus and stiffness a steel lintel needs.
Standard: AS 3700 arching action (45° load triangle) · AS/NZS 1170.0 1.2G + 1.5Q · steel lintel fy, span/500
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 |
|---|---|---|
| Clear opening | 2.4 | m |
| Bearing length each end | 0.15 | m |
| Masonry thickness on the lintel | 110 | mm |
| Masonry unit weight | 19 | kN/m³ |
| Height of masonry above the lintel | 1.8 | m |
| Floor/roof dead load on the wall above | 4 | kN/m |
| Floor/roof live load on the wall above | 1.5 | kN/m |
| Lintel steel fy | 300 | MPa |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Effective span Lo + bearing | 2.55 | m |
| Triangle height Le/2 | 1.28 | m |
| Arching (masonry ≥ triangle + 0.3 m above) | 1.00 | 1 = yes |
| Masonry weight per m height × m | 2.09 | kN/m² |
| Service load (for deflection) | 1.78 | kN/m |
| V* | 2.04 | kN |
| M* (triangle: 1.2·wm·Le³/24; else full UDL) | 1.73 | kNm |
| Required Z = M*/(0.9fy) | 6,418 | mm³ |
| Required I for span/500 (UDL equivalent) | 958,881 | mm⁴ |
- ✓ Arching assumed (enough masonry above)
Method, formulas and assumptions
- Effective span Lo + bearing = 2.4+0.15 = 2.55 m
- Triangle height Le/2 = 2.55/2 = 1.275 m
- Arching (masonry ≥ triangle + 0.3 m above) = IF(1.8>=1.275+0.3,1,0) = 1 1 = yes
- Masonry weight per m height × m = 19*110/1000 = 2.09 kN/m²
- Service load (for deflection) = IF(1=1,2.09*2.55/3,2.09*1.8+4+0.7*1.5) = 1.7765 kN/m
- V* = IF(1=1,1.2*2.09*2.55^2/8,(1.2*(2.09*1.8+4)+1.5*1.5)*2.55/2) = 2.0385 kN
- M* (triangle: 1.2·wm·Le³/24; else full UDL) = IF(1=1,1.2*2.09*2.55^3/24,(1.2*(2.09*1.8+4)+1.5*1.5)*2.55^2/8) = 1.7328 kNm
- Required Z = M*/(0.9fy) = 1.7328*1000000/(0.9*300) = 6417.6 mm³
- Required I for span/500 (UDL equivalent) = 5*1.7765*2.55^4*1E12/(384*200000*2.55*1000/500) = 9.589e+5 mm⁴
- Arching needs adequate masonry each side of the opening to resist the thrust and no openings or movement joints within the arch zone; otherwise design for the full load. Concentrated loads within the triangle must be added.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.