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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.

 

Reinforced Concrete Slab Design Example 1 Figure 1.jpg

 

 

 

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

 

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.

 

Reinforced Concrete Slab Design Example 1 Figure 2.jpg
 

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.

 


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