## Reinforced Concrete Slab Design

### Example 1. One-way Slab

The specified
design strength of the concrete, is 25 MPa () and the specified yield strength of the reinforcement, *f _{y}* , is 400 MPa. The unit weight of reinforced concrete
is assumed to be 24 kN/m

^{3}.

A
one-way slab and beam system is shown below. The slab supports a live load of 4.8
kN/m^{2} and a superimposed dead load of 1.6 kN/m^{2}. Assume
an exterior exposure.

Because
the ratio of the long to short clear spans of the slab panels is 2 or more, the
behaviour of the slab panels is essentially one-way, spanning in the short
direction. One design approach is to use CSA A23.3-04-Appendix B with *m = 0.5*. An alternative to this is to
design the slab as a continuous one-way beam.

**Step 1 ****-**** Slab Thickness (CSA
Clause 9.8.2.1)**

Deflection
requirements (Table 9-2 of CSA A23.3)

Exterior
span 1-1'

Interior
span Try *h _{s}* =

*125*mm

**Step 2 ****-**** Design Moments**

Factored Loading

For design strip 1 metre wide, *wf = 12.95 *kN/m

Limitations for use of Clause 9.3.3 are satisfied;

use coefficients in Clause 9.3.3.

**Step 3 ****-**** Select Reinforcement**

Assume
10M reinforcement

**Minimum Reinforcement**

Try 10M at 400 c/c

Check crack control:

At least minimum reinforcement will
be provided for bottom steel in both directions. The principal reinforcement in
the North-South direction will be in the outside layer. The reinforcement in the non-spanning
East-West direction is more critical for crack control.

For *s = 400 *mm

For an exterior exposure, *z* should be less than 25,000. This
suggests that a spacing of 400 mm is too large. Revise spacing to 350 mm.

Resisting moment at minimum
reinforcement:

This is adequate for all
bottom steel requirements and for top steel on gridline 1. For top steel at
interior supports try *s = 300 *mm*.*

This is sufficient at
all interior supports.

**Use: 10M at 350 c/c bottom
each way. **

** 10M
at 350 c/c top North-South at perimeter beam.**

** 10M
at 300 c/c top North-South at interior beams.**

Transverse reinforcement
over girders spanning parallel to slab is governed by (10.5.3.2).

**Use: 10M at
300 c/c top East-West over all girders.**

**Step
4 ****-****
Check Shear**

*d _{v}* is larger of:

**OK**

**Step
5 ****-****
Design Supporting Beams**

Beams
and girders designed for vertical reaction from slab, self-weight of beam stem,
and any other loads applied directly to beams.
Edge beams also designed for torsion corresponding to negative support
moments assumed in slab design.