Slab Design

RC slab flexural design and capacity check. ACI 318-25, Eurocode 2, IS 456:2000.

Input Parameters

ACI 318-25

Section Geometry

m
m
Material Properties
MPa
MPa
Loading
kN·m/m
—
ACI 318-25 §21.2.2: φ = 0.90 for tension-controlled (εt ≥ 0.005)
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Input Parameters

EN 1992-1-1

Section Geometry

m
m
Material Properties
MPa
MPa
Partial Safety Factors
Loading
kN·m/m
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Input Parameters

IS 456:2000

Section Geometry

m
m
Material Properties
MPa
MPa
Loading
kN·m/m
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Input Parameters

ACI 318-25
m
m
Material Properties
MPa
MPa
Reinforcement (ACI Notation: #Bar @ spacing)
mm
m
#4@200
Demand (for D/C ratio)
kN·m/m
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Input Parameters

EN 1992-1-1
m
m
Material Properties
MPa
MPa
Reinforcement (EC2 Notation: Ø db / spacing)
mm
m
Ø12/150
Demand (for D/C ratio)
kN·m/m
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Input Parameters

IS 456:2000
m
m
Material Properties
MPa
MPa
Reinforcement (IS Notation: Tdb @ spacing c/c)
mm
m
T12@150 c/c
Demand (for D/C ratio)
kN·m/m
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Input Parameters

ACI 318-25 · kN-m
Slab Properties
mm
MPa
mm
mm
Column Properties
mm
mm
Loading
kN
kN·m
kN·m
Shear Reinforcement (optional)
Slab Opening (optional)
Drop Panel (optional)
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Input Parameters

EN 1992-1-1 · kN-m
Slab Properties
m
MPa
m
m
d = h − cv − db = 0.209 m
%
%
Column Properties
m
m
Loading
kN
kN·m
kN·m
Shear Reinforcement (optional)
Drop Panel (optional)
Slab Opening (optional)
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Input Parameters

IS 456:2000 · kN-m
Slab Properties
mm
N/mm²
mm
mm
d = h − cv − db = 209 mm
Column Properties
mm
mm
Loading
kN
ℹ IS 456:2000 Cl 31.6 does not explicitly include moment transfer effects.
Moment Transfer (optional — ACI approach)
Shear Reinforcement (optional)
Drop Panel (optional)
Slab Opening (optional)
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Design Background

Unit Strip Method

One-way slabs are designed per unit width (b = 1 m). The slab is treated as a series of rectangular beams, 1 m wide, spanning in the short direction. Loads, moments, and reinforcement are all expressed per meter width.

Effective Depth

ACI 318-25 — Effective Depth
d = h − ccover − db/2
(No stirrups in slabs — no additional offset for shear links)

Flexural Design (ACI 318-25)

ACI 318-25 §22.2
Rn = Mu / (φ · b · d²)
ρ = (0.85f'c / fy) · [1 − √(1 − 2Rn / 0.85f'c)]
As,req = ρ · b · d

Minimum Reinforcement — Table 7.6.1.1

ACI 318-25 §7.6.1.1
ρmin = max(0.0018 × 420 / fy , 0.0014) for deformed bars
As,min = ρmin · b · h (uses gross depth h, not d)

Maximum Bar Spacing — §7.7.2.3

smax = min(3h, 450 mm)

Effective Depth

EN 1992-1-1
d = h − cnom − db/2

Flexural Design (EN 1992-1-1 §6.1)

EC2 — Lever Arm Method
K = MEd / (b · d² · fcd)
z = d · [0.5 + √(0.25 − K / 1.134)] ≤ 0.95d
As,req = MEd / (fyd · z)
where fcd = fck/γc, fyd = fyk/γs

Minimum Reinforcement — §9.3.1.1

As,min = max(0.26 · fctm/fyk , 0.0013) · b · d
fctm = 0.30 · fck2/3 for fck ≤ 50 MPa

Maximum Bar Spacing — §9.3.1.1(3)

smax = min(3h, 400 mm) for the principal direction

Effective Depth

IS 456:2000
d = D − ccover − db/2

Flexural Design (IS 456:2000 Annex G)

IS 456:2000 — Neutral Axis Method (Limit State)
Solve for xu from: 0.36 · fck · b · xu · (d − 0.42 · xu) = Mu
Ast = 0.36 · fck · b · xu / (0.87 · fy)
Limit: xu ≤ xu,max (singly reinforced limit)

Neutral Axis Limit — Table E

fy = 250: xu,max/d = 0.53  |  fy = 415: 0.48  |  fy = 500: 0.46  |  fy = 550+: 0.44

Minimum Reinforcement — Cl 26.5.2.1

Ast,min = 0.0012 · b · D for fy ≥ 415 MPa (HYSD bars)
Ast,min = 0.0015 · b · D for mild steel (fy = 250 MPa)

Maximum Bar Spacing — Cl 26.3.3(b)

smax = min(3d, 300 mm)