> ## Documentation Index
> Fetch the complete documentation index at: https://calcs.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Design a Concrete Beam to AS 3600:2018
> Design rectangular concrete beams to AS 3600:2018 (Amdt 2) with unlimited spans. Checks flexure, shear, and short- and long-term deflection.
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.
Our rectangular concrete beam calculation allows analysis and design of a multi-span, multi-load beam to AS3600:2018.
## Worked example
### Simply supported and continuous RC beam worked examples
[How to Design a Concrete Beam Using AS3600:2018 in Calcs.com](https://fast.wistia.com/embed/medias/jb727wl2hq) from [Calcs.com](https://clearcalcs.wistia.com/medias/jb727wl2hq).
## Method & scope
| Property | Detail |
| ---------------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | AS 3600:2018 (Amdt 2) |
| Regions | Australia & New Zealand |
| Presets | Generic Indoor Beam, Retaining Wall Sleeper |
| What it checks | Flexural capacity (AS 3600:2018, Cl 8.1), Shear capacity (AS 3600:2018, Cl 8.2, simplified method), Deflection checks (AS 3600:2018, Cl 8.5) |
#### See the exact clause
Every check in this calculator links back to its governing clause in AS 3600:2018. Open the **Formula Reference** panel on any result and select the clause reference to read it. See [Viewing Clauses from Inside a Calculator](/docs/running-calculations/standards-and-codes/viewing-clauses-from-inside-calculator).
#### Calculation method
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.
## How to use it
Open it from **Run calc** in the About this calculator panel above. To start from a typical setup, choose one of the presets listed there.
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See [Checks, References, Conditions and Assumptions](/docs/running-calculations/checking-results/checks-references-conditions-assumptions).
Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export).
#### Rectangular concrete beam design to AS3600-2018 webinar & slides
The following webinar gives an overview of concrete beam design and worked examples using the Calcs.com concrete beam module ( *Jump to 29 minutes for worked examples*).
*Video:*
*Slides:*
[**Designing a Concrete Beam Using the New AS3600:2018 - Webinar Slides - Calcs.com**](https://www.slideshare.net/clearcalcs/designing-a-concrete-beam-using-as3600-2018-webinar-slides-Calcs.com) from [**Calcs.com**](https://www.slideshare.net/clearcalcs)
## Available presets
Each preset opens the calculator with a typical setup already entered.
| Preset | Open in Calcs.com |
| --------------------------------------------- | ------------------------------------------------------------------------------------------------- |
| Generic Indoor Beam | [Run with preset](https://app.calcs.com/new/sheet/concreteBeamRectangular?presetCode=genericBeam) |
| Retaining Wall Sleeper | [Run with preset](https://app.calcs.com/new/sheet/concreteBeamRectangular?presetCode=RWsleeper) |
## Common questions
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.
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.).
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.
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.
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.
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.
## Next steps
Design rectangular and circular reinforced concrete columns to AS 3600:2018 (Amdt 2), with P-M interaction, biaxial bending, slenderness and shear.
Design concrete pad footings to AS 3600:2018 (Amdt 2) with instant moment, shear and punching shear results.
Calculate tension and compression development lengths for reinforcement to AS 3600:2018 (Amdt 2), with code references and modification factors.
Changes in AS3600:2018 Amendment 2 (Concrete)
