Preliminary structural sizing
Spans, loads and ground: the tool sizes the slab, beam, column, footing, load-bearing wall and stair to the Eurocodes, and says which one fails.
The building
Occupancy (imposed load) : Residential (2 kN/m²)
Distance between supports. This is the parameter that governs the depth.
Load take-down
- Slab self-weight
- 6.5 kN/m²
- Finishes
- 1.5 kN/m²
- Ceiling and services
- 0.25 kN/m²
- Partitions
- 1 kN/m²
- Imposed load
- 2 kN/m²
- Design action (1.35 G + 1.5 Q)
- 15.49 kN/m²
Checks an engineer must confirm
Slab
260 mm
- Design bending moment
- 30.98 kNm/m
- Reinforcement provided
- HA8 @ 125 mm
- Steel required
- 367 mm²/m
- Deflection (span/depth)260 mm ≥ 260 mm
- Section adequate in bendingK = 0.0298 ≤ 0.167
- Reinforcement buildableHA8 e = 125 mm (402 ≥ 367 mm²/m)
Beam
200 × 400 mm
- Design bending moment
- 84.37 kNm
- Shear
- 84.37 kN
- Reinforcement provided
- 8 HA10 (2 layer(s))
- Deflection400 mm ≥ 250 mm
- Section adequate in bendingK = 0.1309 ≤ 0.167
- Shear1.18 > 0.59 MPa, cadres calculés nécessaires
- Reinforcement buildable8 HA10 en 2 nappe(s) (628 ≥ 623 mm²)
Column
300 × 300 mm
- Axial load
- 247.84 kN
- Reinforcement provided
- 4 HA10
- Slenderness λ
- 24.2
- Axial capacity300×300 mm ≥ 300² mm requis (e₀ = 20 mm)
- Reinforcement ratio0.2 % ≤ 4 %
- Slenderness (EN 1992-1-1 §5.8.3.1)λ = 24.2 ≤ λ_lim 24.5
Footing
1.2 × 1.2 m
- Thickness
- 300 mm
- Bearing pressure
- 141.75 / 150 kPa
- Utilisation
- 95 %
- Bearing pressure141.75 ≤ 150 kPa
- Minimum thickness300 mm ≥ 250 mm
Foundation system
Each option is genuinely sized rather than given a multiplier. A raft answers weak ground; piles answer ground that will not carry at all.
- Footing
- 1.2 × 1.2 m
- Thickness
- 300 mm
- Bearing pressure
- 141.75 kPa
Upper floor system
A solid slab, a beam-and-block floor and timber joists carry the same load in very different ways, and the self-weight feeds straight back into the columns and foundations.
- Thickness
- 260 mm
- Steel
- 367 mm²/m
On-site drainage
Mains drainage is rare: for most buildings this is the drainage system. It is the soakaway that fails, not the tank.
- People served
- 5
- Tank
- 3.0 m³
- Retention
- 138 h
- Drainage field
- 35 m²
The common favourable case.
Durability and cover
Cover is not a constant: it follows from the exposure class (EN 206) and how well the steel fixing is controlled on site (EN 1992-1-1 §4.4.1). The freeze-thaw classes do not apply here.
Nominal cover: 50 mmSuggested from the city you chose
Applies to any coastal build on the continent; which town that is comes from the country pack. Rightly ignored inland.
The XF freeze-thaw classes are deliberately absent: water does not freeze in a structure here, and carrying them would add cover and cement for no reason.
The same bay in steel
Sized on the concrete frame’s own loads above, so the comparison is like for like. EN 1993-1-1.
Turkey, EuropeThe usual South African and European grade.
Erected cost (one bay): $895 – $1,488484 kg, bare steel $559 – $620
Beam
IPE 240
Mass 123 kg · Utilisation 84% · Deflection 12.3/16 mm
Column
HEA 120
Mass 60 kg · Utilisation 70% · χ = 0.509
Preliminary sizing to EN 1993-1-1: bending resistance, column buckling and deflection. It does not cover lateral torsional buckling, connections, fire or fatigue. Have an engineer confirm it.
Load-bearing wall
The cheapest block that carries the load with a 15% margin. You can pick another and the calculation follows.
Recommended block
Hollow block 20 × 20 × 40
- f_k
- 1.92 MPa
- N_Rd
- 106.4 kN/m
- N_Ed
- 84.6 kN/m
- Utilisation
- 80 %
Other blocks that work : Solid block 15 × 20 × 40 (71 %) · Hollow half block 20 × 20 × 20 (80 %) · Hollow block 25 × 20 × 40 (58 %) · Fired brick, double leaf (22 cm) (56 %)
Blocks ruled out : Hollow block 10 × 20 × 40: Not strong enough · Hollow block 15 × 20 × 40: Not strong enough · Hollow half block 15 × 20 × 20: Not strong enough · Fired brick 22 × 10.5 × 10.5: Not strong enough · Sun-dried earth brick (adobe): Not strong enough · Compressed stabilised earth block: Not strong enough
Stair
16 × 188 / 255 mm
- Width
- 900 mm
- Blondel 2R + G
- 630 mm
- Flights
- 1
- Plan footprint
- 3.44 m²
- Concrete
- 0.874 m³
- Riser height188 ≤ 190 mm
- Going255 ≥ 250 mm
- Blondel rule (2R + G)630 mm dans 600–650
- Clear width900 ≥ 900 mm
- Intermediate landing16 contremarches, volée unique
Preliminary sizing to the Eurocodes, intended to frame a budget and sanity-check an order of magnitude. It is not a structural design and does not replace a registered structural engineer. No structure should be built on this basis alone.