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AS 3600:2018 (Amdt 2)Australia

Concrete Beam

Beam reactions link to connected column and footing calculations automatically - change a load once and everything downstream updates. Design rectangular reinforced concrete beams to AS 3600:2018 (Amdt 2) with the FEA engine handling unlimited supports and loads; checks cover positive and negative flexural capacity, shear, and short- and long-term deflection.

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What it calculates

Beam reactions link to connected column and footing calculations automatically. Design rectangular concrete beams to AS 3600:2018 (Amdt 2) with unlimited spans; checks cover positive and negative flexural capacity, shear, and short- and long-term deflection.

Code standards

  • AS 3600:2018 (Amdt 2)

How it calculates

The Concrete Beam calculator designs rectangular reinforced concrete beams to AS 3600:2018 (Amendment 2) using limit state design. A live FEA engine resolves internal forces for unlimited span and load configurations, and checks are performed for flexure, shear, and deflection at critical sections.

Flexural capacity (AS 3600:2018, Cl 8.1)

Positive and negative moment capacities are computed using the rectangular stress block. For a singly reinforced section:

phi × M_u = phi × A_st × f_sy × (d - gamma × k_u × d / 2)

where gamma is the rectangular stress block depth factor (0.85 - 0.007 × (f'c - 28) ≥ 0.67), k_u is the neutral axis parameter, and d is the effective depth. The strength reduction factor phi = 0.80 for bending per Cl 2.2.2.

Minimum reinforcement (Cl 8.1.6.1) is enforced:

A_st,min = 0.20 × (D/d)² × (f'ct,f / f_sy) × b_w × d

where f'ct,f is the flexural tensile strength of concrete.

Shear capacity (AS 3600:2018, Cl 8.2, simplified method)

The design shear strength without shear reinforcement (Cl 8.2.4.3):

V_uc = beta_1 × beta_2 × beta_3 × b_v × d_v × sqrt(f'c)

where beta_1 accounts for the shear span-to-depth ratio, beta_2 for axial force, and beta_3 for the depth effect. Where fitments are provided, the total design shear strength is:

phi × V_u = phi × (V_uc + V_us)

with V_us = (A_sv / s) × f_sy.f × d_v × cot(theta_v).

Deflection checks (AS 3600:2018, Cl 8.5)

Three deflection limits are verified:

  • Short-term deflection: using the effective moment of inertia I_ef under short-term service loads
  • Long-term deflection: adding a creep/shrinkage multiplier k_cs to the sustained-load deflection
  • Imposed load deflection: deflection due to live load only, checked against the imposed deflection limit

The effective moment of inertia from Cl 8.5.3.1:

I_ef = I_cr + (I_g - I_cr) × (M_cr / M_s)³ capped at I_g

Results are checked against user-defined L/n deflection limits.

Assumptions

No torsional demands are considered. Prestressing and post-tensioning are not included. Secondary effects on shear (V_uc) and load reversal are not considered. Beams are assumed to be enclosed within the building. Concrete detailing (bar laps, anchorage, hooks) is checked separately using AS 3600:2018 Cl 13.

Related calculators

Concrete Column→Concrete Pad Footing→Concrete Development Length→

Frequently asked questions

What design standard and method does this calculator use?
Limit state design to AS 3600:2018 (Amendment 2). Factored loads from AS 1170.0 load combinations are compared to design capacities for flexure and shear. Deflection checks use serviceability load combinations.
What are the key inputs?
Key inputs are cross-section dimensions (breadth b_w and overall depth D, in mm), concrete compressive strength f'c, concrete weight class (normal or lightweight), reinforcement yield strength f_sy, clear cover, positive and negative longitudinal reinforcement (bar size and count), fitment (stirrup) size and spacing, span geometry, support conditions, and applied loads by type (dead, live, wind, etc.).
What checks does the calculator perform?
The calculator checks: positive moment capacity phi × M_u+ ≥ M* (AS 3600:2018 Cl 8.1), negative moment capacity phi × M_u- ≥ M* (Cl 8.1), shear capacity phi × V_u ≥ V* (Cl 8.2 simplified method), governing short-term deflection, governing long-term deflection (with creep factor k_cs), and imposed load deflection. Minimum reinforcement (Cl 8.1.6.1) is also enforced.
How is the effective moment of inertia calculated for deflection?
The cracked-section effective moment of inertia follows AS 3600:2018 Cl 8.5. The short-term deflection uses I_ef based on the cracking moment M_cr and applied moment M_s. Long-term deflection adds a time-dependent multiplier k_cs that accounts for creep and shrinkage under sustained loads.
What shear assumptions apply?
Shear uses the simplified method (Cl 8.2.4.3), valid for f'c up to 65 MPa with no prestress, tension, or torsion. The maximum shear at supports is taken directly over or at any distance from the support - the Cl 8.2.3.2 reduction at a distance d_v from the support face is not applied.
How does load linking work with column and footing calculations?
Beam support reactions link directly to connected column and footing calculations in the same Calcs.com project. When any load or geometry changes in the beam, the downstream column and footing calculations update automatically, keeping the full gravity load path consistent without manual data transfer.

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