concrete cover tolerance? 2

[boffintech]

ACI318 section 7.7 — Concrete protection for reinforcement list the minimum cover for concrete: "The following minimum concrete cover shall be provided for reinforcement..."

Is there a tolerance for the various minimum cover requirements?

 

[henri2]

Yes indeed there is; for tolerances for both minimum cover and effective depth of section. Check the table in Section 7.5.2.1

PCA Notes on ACI 318 explains how to apply the tolerances for cover.

While section 7.5.2.1 provides tolerance for minimum cover, implicit in the tolerance for effective depth of section (d), there is also a tolerance for maximum concrete cover.

 

[boffintech]

Section 7.5.2.1 reads "Tolerance for depth d, and minimum concrete cover in flexural members, walls and compression
members shall be as follows:..."

So the cover requirements for top and bottom bars in slabs either elevated or on-ground is absolute (no tolerance), right?

 

[henri2]

As you are aware, the design engineer will compute the cover, ensure it meets requirements in Section 7.7 and then indicate the required minimum cover in the General Notes under either the sub-heading Reinforcing Steel or Concrete. In some cases cover can also be shown in a schedule and or detail.

The concrete cover shown in the structural plans does not typically include tolerance and neither do the values indicated in ACI 318 Section 7.7; but that does not mean these are absolute minimum values because Gen Notes/Specs will typically cite ACI 318. As you are now aware, ACI Sec 7.5.2.1 does provide for tolerances. Also many job specs refer to ACI 117---Standard Tolerances for Concrete Construction and Materials. For most special inspectors, the provisions for concrete cover in Sec 2 of ACI 117 are easier to comprehend than the provisions outlined in ACI 318.

To use Section ACI 318 Section 7.5.2.1, you have to know what effective depth of section (d) means. The definition is provided in Chapter 2 of ACI 318. In most cases, it will be the distance from the centroid (center) of tension steel to the far face or surface as illustrated in the section of the one-way slab Figure 1 in

http://www.must.edu.my/tkchan/chan-li2001.pdf

.If there was no CFRP plate at the bottom, the d will be equal to 76 mm (approximately 3 inches).

Let's apply ACI 318 Section 7.5.2.1 to a 7-inch thick interior suspended one-way slab(beam slab construction) with a specified cover of 1 inch for flexural steel. Since d is less than 8 inches, the minus tolerance for cover will be -3/8 inch, however for the bottom steel, the tolerance will be -1/4 inch due to the soffit tolerance. You must appy the most restrictive requirement. This means for top steel, minimum acceptable tolerance = (1 inch) - (3/8 inch) = 5/8 inch, while for the bottom steel minimum acceptable cover = (1 inch) - (1/4 inch) = 3/4 inch. Anything less than these values will not be in compliance.