Eccentric Isolated Footing Designer — IS 456:2000

Input Data

Parameter	Value	Unit
Column size — a (along X) × b (along Y)	×	m
Service axial load N_ser (column only; footing weight added internally)		kN
Service moments — M_x (about Y-axis) / M_y (about X-axis)	/	kN·m
Column position mode		—
Physical eccentricity — e_x (column C/L offset along X) / e_y (along Y)	/	m
Edge distances — column face to footing edge: left / right (along X)	/	m
Edge distances — column face to footing edge: bottom / top (along Y)	/	m
Concrete grade f_ck		MPa
Steel grade f_y		MPa
Allowable SBC (gross, at foundation level)		kN/m²
Auto-suggest B, L, t — fills footing dimensions below (targets 95% SBC)		—

Footing plan size — B (along X) × L (along Y)	×	m
Overall footing thickness t		m
Clear cover to bottom bar face (IS 456: min 50 mm for footings on soil)		mm
Bottom bar dia — X-dir. ϕ_x (outer/lower layer) / Y-dir. ϕ_y (inner layer) d_x = t−cover−ϕ_x/2 \| d_y = t−cover−ϕ_x−ϕ_y/2	X: Y:	mm
Top bar dia — X-dir. ϕ_top,x (outer at top) / Y-dir. ϕ_top,y (inner) d_top,x = t−cover−ϕ_top,x/2 \| d_top,y = t−cover−ϕ_top,x−ϕ_top,y/2	X: Y:	mm
Column dowel diameter ϕ_d		mm

⚠ Cover < 50 mm — IS 456 Cl.26.4 recommends min. 50 mm for footings on soil.

⚠ Footing thickness < 250 mm — review shear and punching adequacy.

⚠ d_y ≤ 0 — Y-bar inner layer has no effective depth. Increase t or reduce bar sizes / cover.

⚠ Footing smaller than column — B must be > a and L must be > b.

Total e_x, e_y

—

q_max / q_min (kN/m²)

—

d_x / d_y / d_avg (mm)

—

Codal Checks — IS 456:2000

Check	Rule / Clause	Values & Utilization	Status

Fill required inputs (marked *) to begin.

Bottom Steel — X-direction (outer layer, d_x)

Parameter	Value	Unit
Bar diameter ϕ_x	—	mm
Effective depth d_x	—	mm
Governing cantilever l_x	—	m
Design moment M_ux	—	kN·m/m
A_s,x required	—	mm²/m
Provided spacing	—	mm c/c
A_s,x provided	—	mm²/m

Bottom Steel — Y-direction (inner layer, d_y)

Parameter	Value	Unit
Bar diameter ϕ_y	—	mm
Effective depth d_y	—	mm
Governing cantilever l_y	—	m
Design moment M_uy	—	kN·m/m
A_s,y required	—	mm²/m
Provided spacing	—	mm c/c
A_s,y provided	—	mm²/m

Top Steel near Column — Hogging (IS 456 strip method)

Parameter	Value	Unit
Hogging moment — X strip (M_hog,x)	—	kN·m/m
A_s,top,x required	—	mm²/m
Provided spacing — X top (ϕ_top,x)	—	mm c/c
A_s,top,x provided	—	mm²/m
Hogging moment — Y strip (M_hog,y)	—	kN·m/m
A_s,top,y required	—	mm²/m
Provided spacing — Y top (ϕ_top,y)	—	mm c/c
A_s,top,y provided	—	mm²/m

Min. top steel = 0.12% bD (IS 456 Cl.26.5.2.1) always provided; hogging adds if > min.

Engineering Drawings

Run a calculation to generate drawings.

Bar Bending Schedule (BBS)

Run a calculation to generate BBS.

Design Calculation Summary

Design Assumptions & Method

Code: IS 456:2000 (Limit State Method); isolated footing design per Cl.34.
Soil pressure (service): Gross load = N_col + W_self checked against SBC. Trapezoidal distribution; effective area method when load falls outside kern (B/6, L/6).
Net factored upward pressure (RC design): q_u = 1.5 × (N_col/A) × distribution. Footing self-weight cancels with its share of soil pressure in bending/shear — correctly excluded from q_u. Eccentricities computed conservatively from gross N.
Bar layers: X-bars are the outer (lower) layer; Y-bars placed on top of X-bars as inner layer. Each direction uses its own effective depth for flexure and one-way shear.
Effective depths: d_x = t − cover − ϕ_x/2 (X, outer); d_y = t − cover − ϕ_x − ϕ_y/2 (Y, inner).
Punching shear: Critical perimeter at d_avg/2 from column face; d_avg = (d_x + d_y)/2 (IS 456 Cl.31.6). k_s = min(0.5 + β_c, 1.0); v_c = k_s × 0.25√f_ck. Guard applied: perimeter ≤ 0 is skipped.
One-way shear: Critical at d from column face. X-direction uses d_x; Y-direction uses d_y. τ_c from IS 456 Table 19 (linear interpolation); τ_v,max = 0.62√f_ck (Table 20).
Minimum steel: 0.12% × b × D per IS 456 Cl.26.5.2.1 for HYSD bars (Fe415/500). τ_c in checks uses actual provided percentage, not a constant.
Max. bar spacing: min(3d, 300 mm) per IS 456 Cl.26.3.3 for main bars in slabs.
Development length (tension, deformed bar): L_d = ϕ × 0.87f_y / (4 × τ_bd × 1.6) — IS 456 Cl.26.2.1.1. Checked against SHORTER cantilever (critical end). Hooks required if L_avail ≤ 0.
Dowel compression L_d: 0.8 × L_d,tension per IS 456 Cl.26.2.1.2.
Column bearing: IS 456 Cl.34.4 — 0.45 × f_ck × A₁ × √(A₂/A₁), √ratio ≤ 2. Min. dowels = 0.5% A_column.
Top steel (hogging): Strip method — factored P_u as point load at column centroid, uniform q_u upward; negative moment by equilibrium.
Suggest function: Uses same dual-depth model (d_x, d_y, d_avg), actual p_t for τ_c, and correct net factored pressure. Self-weight included in soil check; excluded in bending pressure.
Unit weight of concrete: 25 kN/m³. Bond stress τ_bd: IS 456 Table 26.2.1 × 1.6 for HYSD bars.

Disclaimer: This calculator is a design aid based on IS 456:2000. Results must be independently verified by a licensed structural engineer before use in construction. The tool does not account for seismic loads, differential settlement, site-specific conditions, or all detailing requirements. The developer accepts no liability for errors or misuse of results.

Eccentric Isolated Footing Designer — IS 456:2000

Input Data

Codal Checks — IS 456:2000

Bottom Steel — X-direction (outer layer, dx)

Bottom Steel — Y-direction (inner layer, dy)

Top Steel near Column — Hogging (IS 456 strip method)

Engineering Drawings

Bar Bending Schedule (BBS)

Design Calculation Summary

Design Assumptions & Method

Bottom Steel — X-direction (outer layer, d_x)

Bottom Steel — Y-direction (inner layer, d_y)