Rectangular Combined Footing Design
Column Loads & Dimensions
| Parameter | Value | Unit |
|---|---|---|
| Column 1 (left) | ||
| Width (B₁) × Depth (D₁) | × | m |
| Service axial load (P₁) | kN | |
| Service Moment about transverse M₁(L) | kN·m | |
| Service Moment about longitudinal M₁(B) | kN·m | |
| Column 2 (right) | ||
| Width (B₂) × Depth (D₂) | × | m |
| Service axial load (P₂) | kN | |
| Service Moment about transverse M₂(L) | kN·m | |
| Service Moment about longitudinal M₂(B) | kN·m | |
| Column Center to Centre spacing (s) | m | |
| Moment design mode | - | |
Materials, Soil & Factors
| Parameter | Value | Unit |
|---|---|---|
| Grade of Concrete (fck) | N/mm² | |
| Grade of steel (fy) | N/mm² | |
| Allowable SBC | kN/m² | |
| γf (service → ultimate) | - | |
| Self-weight of footing (γ=25 kN/m³) is included by default. | ||
Footing Geometry
| Parameter | Value | Unit |
|---|---|---|
| Footing width (B) | m | |
| Footing thickness (t) | m | |
| Clear cover | mm | |
| Minimum edge projection pmin | m | |
| B and t will auto-fill once B₁, D₁, B₂, D₂, P₁, P₂ and s are entered. Overwrite to lock custom values. | ||
Reinforcement Options
| Parameter | Value | Unit |
|---|---|---|
| Main bar dia (along L) | mm | |
| Top main bar dia | mm | |
| Transverse bar dia (across B & L) | mm | |
| Spacing rounding step | mm | |
| Top bars: +30% Ld | IS 456 26.2.1.1 | |
| Integration step for strip | mm |
Codal Checks (IS 456) — OK / Not OK
| Check | Rule / Clause | Utilization & Key Values | Status |
|---|
Summary
| Summary Parameter | Value | Unit |
|---|---|---|
| Footing size (B × L × t) | — | m |
| Projections (left / right) | — | m |
| q (service) / SBC | — | kN/m² |
Reinforcement Summary
Bottom (sagging) along L, Top (hogging) along L, Transverse across B and along L. LD checks added.
Detailed Calculations (numeric trace)
Assumptions & Limitations
- Uniform soil pressure (rigid) for service sizing; SBC check shown on service; sizing targets 0.95×SBC.
- Ultimate checks use γf (default 1.5): Pu=γfP, Mu=γfM; qu from final B×L.
- Uniaxial(L): column M(L) as couples at column lines; biaxial adds |M(B)|/s per m (conservative).
- LD per IS 456 Table 21 (deformed ×1.6); top +30% option; anchorage from faces.
- Spacing rounding is floor to step (5/10/25/50 mm) with global minimum spacing = 75 mm.
- Suggested geometry minimizes volume over discrete B,t grids subject to codal checks and target q≈0.95×SBC; L rounded up to 0.25 m.
- Self-weight (γ=25 kN/m³) included by default.