Search
Close this search box.

How to Use a Concrete Slab Load Capacity Calculator:

  1. Input Data Collection: Begin by gathering necessary parameters like slab thickness, concrete strength, reinforcing yield, subgrade modulus, and load data.
  2. Enter Inputs: Fill in the collected parameters into the appropriate fields, such as slab thickness, concrete unit weight, subgrade modulus, etc.
  3. Run Calculation: Click the “Calculate” button to run the analysis, which will compute flexural stress, bearing stress, punching shear, and other critical factors.
  4. Interpret Results: Review the results, including stress values, crack width, and permissible stresses. Compare them against allowable limits to ensure the design is safe.
  5. Adjust Design if Needed: Based on the results, modify input parameters (e.g., increase slab thickness or reinforcement) and rerun the calculations to find the optimal solution.

Example Calculatio: Concrete Slab Load Capacity Calculator

Scenario:

  • Slab Thickness: 6 inches
  • Concrete Strength: 4000 psi
  • Reinforcing Yield: 60000 psi
  • Subgrade Modulus: 100 pci
  • Concentrated Load: 5000 lbs
  • Contact Area: 50 in²
  • Safety Factor: 1.5

Steps:

  1. Effective Load Radius (a): a = sqrt(Contact Area / pi) = sqrt(50 / pi) ≈ 4.0 in
  2. Modulus of Elasticity (Ec): Ec = 33 * wc^1.5 * sqrt(f ‘c) = 33 * (145)^1.5 * sqrt(4000) ≈ 3646200 psi
  3. Modulus of Rupture (MR): MR = 9 * sqrt(f ‘c) = 9 * sqrt(4000) ≈ 570 psi
  4. Cracking Moment (Mr): Mr = MR * (12 * t^2 / 6) / 12000 = 570 * (12 * 6^2 / 6) / 12000 ≈ 3.42 ft-k/ft
  5. Radius of Stiffness (Lr): Lr = (Ec * t^3 / (12 * (1 – m^2) * k))^0.25 ≈ (3646200 * 6^3 / (12 * (1 – 0.15^2) * 100))^0.25 ≈ 27.2 in
  6. Flexural Stress (1 Load, fb1): fb1 = (3 * P * (1 + m)) / (2 * pi * t^2) * (log(Lr / a) + 0.6159) ≈ (3 * 5000 * (1 + 0.15)) / (2 * pi * 6^2) * (log(27.2 / 4.0) + 0.6159) ≈ 210 psi
  7. Bearing Stress (fp, actual): fp = P / Ac = 5000 / 50 ≈ 100 psi
  8. Punching Shear Perimeter (bo): bo = 4 * sqrt(Ac) = 4 * sqrt(50) ≈ 28.3 in
  9. Punching Shear Stress (fv, actual): fv = P / (t * (bo + 4 * t)) = 5000 / (6 * (28.3 + 4 * 6)) ≈ 55 psi

Concrete Slab Load Capacity Calculator: