Who checks the z-equation?

[legner]

Chapter 10 of the code requires that the following be satisfied: z &lt;= 175 (interior) or z&lt;= 145 (exterior), where z = f_s (d_c A)^1/3.<br>
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Meeting this requirement can be tricky in a real building. For example, for a structural slab on grade which spans, say, between grade beams, but is built directly on grade, the maximum bar spacing with 3" cover is on the order of 4 inches.<br>
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I do not believe the CRSI design handbook designs meet the z-equations. Does everyone else violate the requirement to arrive at reasonable designs?

 

[wwjk]

Yes. I knowingly violate this provision any virtually all my concrete designs. The provision is unrealistic and impractical.

 

[HochwaltPE]

This provision has been completely rewritten in ACI 318-99. There was also an excellent discussion of this topic by Robert Frosch in the May-June 1999 issue of the ACI Structural Journal.

 

[PJD]

I have heard that the z equation has been totally re-writtenin the new iternational 2000 code. I'll bet it follows ACI to the letter.

 

[HochwaltPE]

The IBC 2000 adopts ACI 99 by reference for concrete design.

 

[legner]

I have a copy of ACI 318-99, and the Z-equation section has been revised. You now directly calculate the reinforcement spacing, and the results thankfully seem more resonable than before.