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# Who checks the z-equation?

## Who checks the z-equation?

(OP)
Chapter 10 of the code requires that the following be satisfied: z <= 175 (interior) or z<= 145 (exterior), where z = f_s (d_c A)^1/3.

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.

I do not believe the CRSI design handbook designs meet the z-equations. Does everyone else violate the requirement to arrive at reasonable designs?

### RE: Who checks the z-equation?

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

### RE: Who checks the z-equation?

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.

### RE: Who checks the z-equation?

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.

### RE: Who checks the z-equation?

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

### RE: Who checks the z-equation?

(OP)
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.

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