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United States
ACI 318-19ACI 318-14

Concrete Beam (ACI 318-14)

Beam reactions link to connected column and footing calculations automatically - change a load once and everything downstream updates. For projects permitted under ACI 318-14 - use the ACI 318-19 version for new designs. Checks flexural strength, shear capacity, and short- and long-term deflection across unlimited spans with customisable top and bottom reinforcement.

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What it calculates

Design rectangular concrete beams to ACI 318-14 with customisable top and bottom reinforcement across unlimited spans. Checks include flexural strength, shear capacity, and short- and long-term deflection. Beam reactions link to connected column and footing calculations so changes propagate automatically.

Code standards

  • ACI 318-14

How it calculates

The Concrete Beam (ACI 318-14) calculator designs rectangular sections per ACI 318-14 using LRFD. The FEA solver envelopes ASCE 7 factored load combinations to find governing Mu+ (positive), Mu- (negative), and Vu.

Flexural capacity

Positive and negative moment capacities φMn are computed using the ACI rectangular stress block at ultimate concrete strain εcu = 0.003. The neutral axis depth c is solved from equilibrium between the concrete compression block and the total steel tension (or combined tension and compression steel for doubly reinforced sections):

a = A_s × fy / (0.85 × f'c × bw)

The nominal moment capacity is:

Mn = A_s × fy × (d - a/2) (for singly reinforced sections)

The strength reduction factor φ = 0.90 for tension-controlled sections (net tensile strain εt ≥ 0.005). A plain concrete section (no reinforcement) is flagged as unsupported.

Shear capacity

Shear capacity φVn = φ(Vc + Vs) where:

  • Vc = concrete contribution per ACI 318-14 simplified formula, modified by λ for lightweight concrete
  • Vs = stirrup contribution = Av × fy × d / s

Utilization = Vu / φVn ≤ 1.0 where φ = 0.75 for shear.

Deflection

Deflection uses the effective moment of inertia Ie = Ig × (Mcr/Ma)³ + Icr × [1 - (Mcr/Ma)³] per ACI 318-14 Cl 24.2.3.5 to account for cracking. Three limit states are checked:

  • Short-term (δST): under live/roof live service loads
  • Long-term (δLT): total with creep and shrinkage multiplier
  • Simplified DL+(LL or SL): combined dead plus governing transient load

Deflection utilization = δ / Δmax ≤ 1.0 against user-defined L/n limits.

Related calculators

Rectangular Concrete Column→Concrete Beam→Rectangular Concrete Column→

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Frequently asked questions

What design method and standard does this calculator follow?
Strength Design Method (LRFD) per ACI 318-14. Factored loads from ASCE 7 LRFD combinations are compared to reduced nominal capacities using the appropriate ACI strength reduction factors.
What are the key inputs?
Cross-section dimensions (width bw and overall depth h, in inches), concrete compressive strength f'c (psi, minimum 2500 psi per ACI 318-14 Cl 19.2.1.1), concrete weight class (normalweight or lightweight, setting the λ factor), reinforcement yield strength fy (40-80 ksi), clear cover, positive and negative moment reinforcement (bar size and count, up to two rows), stirrup size and spacing, span geometry, supports, and factored loads by type.
What checks does it perform?
Positive flexural capacity φMn+ ≥ Mu+, negative flexural capacity φMn- ≥ Mu-, shear capacity φVn ≥ Vu (concrete plus stirrup contributions), short-term deflection, long-term deflection, and simplified DL+(LL or SL) deflection. All results show the demand-to-capacity ratio. Minimum cover and bar spacing requirements are also flagged.
Can it model multi-span continuous beams with different reinforcement in each region?
Yes - the FEA engine handles unlimited spans with configurable support conditions. Reinforcement is specified separately for positive moment regions (midspan) and negative moment regions (supports), reflecting real detailing practice.
Is this the current ACI edition?
This is the ACI 318-14 version. The current edition is ACI 318-19 - use the Concrete Beam (ACI 318-19) calculator for new designs. ACI 318-14 remains valid for projects permitted under earlier IBC editions or jurisdictions that have not adopted the 2019 edition.
Does this calculator support load linking with column and footing calculations?
Yes - beam support reactions link directly to connected column and footing calculations in the same project. When any load or geometry changes in this beam, all linked downstream calculations update automatically.

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