SME
Reinforced Concrete Design · Problem type
Minimum thickness of a one-way slab
Use this for “A one-way slab spans 15 ft with one end continuous. What is its least thickness?”
Diagram
Supports: a pin at A, a fixed end at B.
This is an example. Type your own values to start a new problem.
hₘᵢₙ (cm)
=
ℓ (m)
n
Formulas
hₘᵢₙ
=
12
×
ℓ
n
7.5
=
12
×
15
24
Formulas are worked in ft, in. The step-by-step shows the conversions.
Assumptions
•
ACI 318-19, normal-weight concrete and Grade 60 bars; a slab this thick needs no deflection calculation.
•
n is 20 simply supported, 24 with one end continuous, 28 with both, and 10 for a cantilever.
•
Continuous ends are drawn as fixed; 12 in to a foot.
Step-by-step
WE KNOW
ℓ = 4.572 m, n = 24
FIND
least slab thickness (hₘᵢₙ)
Step 1 · Convert to the formula’s units
The formulas don’t work directly in the units you chose, so convert first (to ft, in).
ℓ = 4.572 m = 15 ft (1 m = 3.28084 ft)
Step 2 · Find least slab thickness (hₘᵢₙ)
Use hₘᵢₙ = 12 × ℓ ÷ n
Turn
the
span
into
inches
(×
12),
then
divide
by
the
support
case’s
n
.
hₘᵢₙ
=
12
×
15
24
hₘᵢₙ
=
180
24
hₘᵢₙ = 7.5 in
Step 3 · Convert the answers
Change each answer back to the unit you chose.
hₘᵢₙ = 7.5 in = 19.05 cm (1 in = 2.54 cm)
Check
Put the numbers back in. Both sides should match.
7.5
=
12
×
15
24
✓
Topic check
See what you know: 5 questions on this topic
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