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Concrete Flat Slab Calculator to AS3600

Verified by the CalcTree engineering team on August 30, 2024
This calculator performs the analysis and design of reinforced concrete two-way spanning slabs supported by columns, i.e. a flat slab. Design actions are calculated using simplified elastic analysis. Flexural capacity and deflection are then checked.
All calculations are performed in accordance with AS3600-2018.

Calculation

Technical assumptions

Slab Properties

RC slab cross-section

Geometry:


B
:1.00 m​



D
:225 mm​



Ly
:5.00 m​



Lx
:4.00 m​



Ly / Lx
:1.25​



Slab_type
:Two-way​


One- or two-way slab


Concrete Properties:


fc
:32MPa​



Ec
:30,100​



Density_c
:25 kN / m^3​

Reinforcement Properties:


fsy
:500 MPa​



Es
:200 GPa​


Reinf in tension zone:


db_st
:16mm​



s_st
:200 mm​



c_st
:25 mm​



d_st
:192 mm​



Ast
:1,005 mm^2​

Reinf in compression zone:


db_sc
:10mm​



s_sc
:200 mm​



c_sc
:25 mm​



d_sc
:30 mm​



Asc
:393 mm^2​



Loads



SW
:5.63 kPa​



SDL
:0.50 kPa​



Q
:2.00 kPa​



Fd
:10.35 kPa​


ULS



psi_s
:0.7​



psi_l
:0.4​



kcs
:1.18​



F_def, total
:15.7 kPa​



F_def, incr
:9.6 kPa​


SLS



Slab Analysis

For two-way slabs supported by columns, as per Clause 6.10.4.

Mo=FdLtLo28M_o= \dfrac{F_dL_tL_o^2}{8}



Mo, interior x
:103.5 kN m​



Mo, interior y
:129.4 kN m​



Mo, edge y
:64.7 kN m​



Mo, edge x
:51.8 kN m​



4x unique per flat slab system


Mcritical section∗={+Mmid span∗,−Minterior or exterior edge∗}=factor×MoM^*_\text{critical section}= \{+M^*_\text{mid span},-M^*_\text{interior or exterior edge}\} =\text{factor}\times M_o

Factor is given in Tables 6.10.4.3(A) & (B)



Exterior_edge_restraint
:Restrained by spandrel beams and columns​



Mcolumn strip∗=column strip moment factor×Mcritical section∗Mmiddle strip∗=(1−column strip moment factor)×Mcritical section∗M^*_\text{column strip}=\text{column strip moment factor}\times M^*_\text{critical section} \\ M^*_\text{middle strip}=(1-\text{column strip moment factor})\times M^*_\text{critical section}


Column strip moment factor is given in Table 6.9.5.3



Neg_moment_at_interior_support
:0.6​



Pos_moment_at_all_spans
:0.6​



Neg_moment_at_exterior_support
:0.75​


Slab analysis

results:
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Can’t display the image because of an internal error. Our team is looking at the issue.


Slab analysis breakdown

❗Ensure these conditions have been met

For flat slabs, the simplified elastic analysis as outputted above is valid if:
  1. 
    
    , where Q = live load & G = dead load
  1. loads are uniformly distributed
  1. at least two continuous spans in each direction
  2. support grid is roughly rectangular
  3. successive span lengths in each direction do not differ by more then 1/3 of the longer span, and the end span cannot be longer then the adjacent interior span
  1. 
    
    at supports are only caused by loads applied to the beam or slab, not from the columns


Flexural (ULS) Design Check



phi
:0.85​


Capacity reduction factor



ku
:0.11​



Check ku
:< 0.36 ✅​


Ductility check



Ast,min
:430 mm^2​



Check Ast
:> Ast,min ✅​


Minimum reinforcement check



α2
:0.80​



γ
:0.89​



Mu
:77.8 kN m​



+M*_max
:38.8 kN m​



-M*_max
:-54.3 kN m​


Moment capacity check



Check +M*
:= 39kNm ≤ Mu = 78kNm, OK ✅​



Check -M*
:= 54kNm ≤ Mu = 78kNm, OK ✅​


Note

  1. For sagging moment
    
    ,
    
    is on the bottom &
    
    on the top
  1. For hogging moment
    
    ,
    
    is on the top &
    
    on the bottom


Deflection (SLS) Check



Slab type
:Ly/Lx = 1.25 ∴ Two-way slab supported by Columns​


Span_type
:Simply supported​



Drop_panels
:Yes​



k3
:1.05​



k4
:1.40​



Lef / d
:26​


Simplified approach

For total deflection:


Deflection_limit_total
:1/250​



(Lef / d)_limit
:29​



Check
:Lef/d ≤ limit ✅​



Min D
:205 mm​

For incremental deflection:


Deflection_limit_incr
:1/500​



(Lef / d)_limit (1)
:27​



Check (1)
:Lef/d ≤ limit ✅​



Min D (1)
:217 mm​


❗Ensure these conditions have been met

As per Clause 9.4.4, for RC slabs, the simplified approach for flat slab deflection is valid if:
  1. loads are uniformly distributed
  2. 
    
    
    check
    :Q = 2.0kPa ≤ G = 6.1kPa, simplified analysis is valid ✅.​
    
  1. uniform slab depth
  2. fully propped during construction
  3. for flat slabs with drop panels, drop panels must extend at least
    
    in each direction on each side of the support centre-line, and have an overall depth not less then
    
    slab thickness beyond the drops
  4. in adjoining spans, the ratio of the longer span to the shorter span does not exceed
    
    , and no end span is longer than an interior span