One-Way Concrete Flat Slab
Slab reactions link to the supporting beams and columns so changes to the structure propagate automatically. Analyse and design one-way concrete flat slabs to AS 3600:2018 (Amdt 2) with live FEA across unlimited spans. Checks positive and negative moment capacity, shear, punching shear, and short- and long-term deflection with hoverable demand diagrams.
14-day free trial - no credit card required
What it calculates
Analyse and design one-way reinforced concrete flat slabs to AS 3600:2018 (Amdt 2) with live FEA and hoverable moment, shear, and deflection graphs. Checks positive and negative moment capacity, shear, and short- and long-term deflection across unlimited spans.
Code standards
- AS 3600:2018 (Amdt 2)
How it calculates
The One-Way Concrete Flat Slab calculator analyses and designs reinforced concrete slabs spanning in one direction to AS 3600:2018 (Amdt 2). A live FEA engine solves the structural model for each load combination, producing moment, shear, and reaction diagrams that update as inputs change.
Structural model and load cases
The slab is modelled as a continuous beam of unit width (1 m) spanning across the entered supports. Supports can be set to pinned, fixed, or continuous (internal). Load cases are generated per AS/NZS 1170.0 strength and serviceability combinations from the entered dead (G), superimposed dead (SDL), live (Q), and long-term live fraction. Self-weight is computed automatically from the slab depth and concrete density.
Positive and negative moment capacity (AS 3600:2018, Cl. 8.1)
Moment demand at each critical section is taken from the FEA results under the governing strength load combination. Positive moment capacity (bottom steel governs) and negative moment capacity (top steel governs) are calculated from the reinforcement area, effective depth, and concrete compressive strength:
utilization = M_u / (phi × M_n) ≤ 1.0
where phi = 0.85 for bending. Minimum reinforcement ratios per AS 3600:2018 Cl. 8.1.6 are checked for both top and bottom faces.
Shear capacity (AS 3600:2018, Cl. 8.2)
One-way shear demand V_u at each support is checked against the concrete shear capacity (no stirrups assumed for a flat slab):
utilization = V_u / (phi × V_n) ≤ 1.0
where phi = 0.75 and V_n is calculated per the simplified method accounting for longitudinal reinforcement ratio and effective depth.
Punching shear (AS 3600:2018, Cl. 9.2)
Punching shear is checked at the critical perimeter around column or drop-panel support areas. The demand V_u* is compared to the punching shear capacity f_cv accounting for the critical perimeter length and effective depth. A warning is raised if the demand-to-capacity ratio approaches 1.0.
Deflection checks (AS 3600:2018, Cl. 8.5)
Three deflection limits are checked:
- Short-term deflection under 1.0G + 1.0Q (elastic FEA result, including cracked section factor k_cs)
- Long-term (total) deflection including creep and shrinkage using the multiplier approach per Cl. 8.5.3
- Imposed load deflection (live load component only, for partition damage limit)
Each deflection is compared to the span/limit ratio (L/250 or L/500 as applicable). The governing span and load case are reported.
Related calculators
What engineers say
I like using different software packages, but the reason why I use Calcs.com more often now is load linking.
Richard Faulkner
Senior Structural Engineer, Kusch Consulting Engineers
I like that Calcs.com shows the code reference section for each calculation and function. That means every time I use it, there's a potential for me to learn something.
Jim Fanjoy
Project Architect, Brittell Architecture
Frequently asked questions
What design standard does this calculator use?
What are the key inputs?
What does the calculator check and output?
Does this calculator support drop panels and spandrel beams?
Does this calculator support load linking with beam or column calculations?
Access this calculator and 100+ more
All verified, standards-aligned. Start a free trial - no credit card required.