Rigid Pavement Thickness Calculator: Concrete Slab Thickness With and Without Dowels
Concrete slab thickness from the textbook formulas.
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Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.
How this calculator works
Choose the slab: without dowels, with dowels at the edge or with dowels at the centre.
Enter the wheel load and the allowable tensile stress of the concrete (or its strength and the fraction allowed).
The calculator gives the slab thickness in metres and millimetres.
Formulas used
- t = \sqrt{\frac{3W}{f}}
- t_1 = \sqrt{\frac{3W}{2f}}\ \text{(edge, dowels)}
- t_2 = \sqrt{\frac{3W}{4f}}\ \text{(centre, dowels)}
Worked example
With the default numbers in the calculator above:
- Wheel load: 56000.00 N
- Allowable tensile stress used: 1.60 MPa
- Thickness of the slab in metres: 0.32 m
- Thickness of the slab in millimetres: 324.04 mm
Change the numbers in the calculator to see the full working, every step, for your own case.
A second worked example
A different case, with these numbers: Slab With dowels, at the edge: t = square root of 3W / 2f.
- Wheel load: 56000.00 N
- Allowable tensile stress used: 1.60 MPa
- Thickness of the slab in metres: 0.23 m
- Thickness of the slab in millimetres: 229.13 mm
Common questions
What does the dowel change?
Dowels pass part of the load to the next slab, so the slab can be thinner. At the edge the value under the root is halved and at the centre it is quartered, compared with a slab without dowels.
What allowable tensile stress should I use?
Use the value your course or standard gives. Some textbooks use a fraction of the concrete compressive strength, for example 0.06 f c, and this calculator can take that.
Is this a pavement design?
No. These are the simple textbook formulas for study. A real design uses the road authority method with traffic, subgrade and joint details.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Any highway or pavement engineering text (rigid pavement thickness). Use the road authority method (for example Austroads) for a real pavement.
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