# Reinforced Concrete Slab Design Example 1

## 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, fy , is 400 MPa. The unit weight of reinforced concrete is assumed to be 24 kN/m3.

A one-way slab and beam system is shown below. The slab supports a live load of 4.8 kN/m2 and a superimposed dead load of 1.6 kN/m2. 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 hs = 125 mm

Step 2 - Design Moments

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

dv 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.

Reinforced Concrete Slab Design Example 1 Figure 6.jpg