Combined Footing Design — IS 456 : 2000

Column Loads & Dimensions

Parameter	Value	Unit
Column 1 (left)
Width (B₁) × Depth (D₁)	×	m
Service axial load (P₁)		kN
Service moment — transverse M₁_(L)		kN·m
Service moment — longitudinal M₁_(B)		kN·m
Column 2 (right)
Width (B₂) × Depth (D₂)	×	m
Service axial load (P₂)		kN
Service moment — transverse M₂_(L)		kN·m
Service moment — longitudinal M₂_(B)		kN·m
Column c/c spacing (s)		m
Moment design mode		—

Materials, Soil & Factors

Parameter	Value	Unit
Grade of concrete (f_ck)		N/mm²
Grade of steel (f_y)		N/mm²
Allowable SBC		kN/m²
Load factor γ_f		—
Self-weight of footing (γ = 25 kN/m³) included automatically.

Footing Geometry

Parameter	Value	Unit
Footing shape		—
Footing width (B)		m
Widths: b̅ / b₁ (left) / b₂ (right)	—	m
Footing thickness (t)		m
Footing length (L) [computed]		m
Clear cover		mm
Min edge projection p_min		m
B and t auto-fill from load data. Overwrite to lock custom values.

Reinforcement Options

Parameter	Value	Unit / Ref
Bottom main bar dia (along L)		mm
Top main bar dia (along L)		mm
Bottom transverse bar dia (along B)		mm
Top transverse bar dia (along B)		mm
Spacing rounding step		mm
Top bars: apply +30% L_d		IS 456 Cl.26.2.1.1
Integration step		mm

Fill in the required column loads (highlighted in red) to begin.

Codal Checks — IS 456 : 2000

Check	Clause / Rule	Key Values & Utilization	Status

Summary

Parameter	Value	Unit
Footing size B × L × t	—	m
Projections left / right	—	m
q_avg / q_max / SBC	—	kN/m²
q_min — uplift check	—	kN/m²

Reinforcement Schedule

Enter loads & geometry to generate schedule.

Reinforcement Diagram

Detailed Calculations

Run computation to see detailed trace.

Assumptions & Limitations

Rigid footing — uniform soil pressure for service sizing; target q ≈ 0.95 × SBC; L rounded up to 0.25 m.
Factored checks use user γ_f (default 1.5); q_u derived from final B × L.
Uniaxial mode applies column M_(L) as moment couples. Biaxial mode adds |M_(B)|/s per m to transverse bending.
SBC eccentricity: q_max by trapezoidal formula; q_min ≥ 0 checked.
Mu,lim: IS 456 Annex G — 0.36 × k_lim × (1 − 0.42k_lim) × f_ck × b × d².
τ_c,max: IS 456 Table 20 values checked alongside τ_c.
Ast,min: 0.12% of gross section b × D, IS 456 Cl. 26.5.2.1.
Transverse bar spacing: max = min(3d, 300 mm), IS 456 Cl. 26.3.3(a).
Shear: All four column faces checked. τ_c uses pt = max(Ast,req,bot, Ast,req,top, Ast,min) / (b × d,top).
Column band (Cl. 34.3.1): Band = D_col + 2d (d beyond each face).
Top transverse bars: Designed at Ast,min for crack control in hogging zone.
Minimum depth: t ≥ 150 mm, IS 456 Cl. 34.1.2.
Lever arm: Ast,req uses 0.9d (standard Indian practice for initial sizing).
Ld per IS 456 Table 21 (deformed ×1.6); top bar +30% per Cl. 26.2.1.1.
Spacing floor to rounding step (5/10/25/50 mm); global min = 75 mm.
Self-weight (25 kN/m³) included; geometry minimises volume subject to all checks.

⚠ Disclaimer: For preliminary design and educational use only. Results must be verified by a qualified structural engineer before use in construction. The authors accept no liability for decisions made based on outputs from this tool.