Tolerances On Placement Of Reinforcing In Concrete Construction

When it comes to concrete or shotcrete construction, how close is close enough? This question comes into play when builders are following a precise construction plan or structural plan. The plans specify both the size of the reinforcing bars but also the spacing, usually denoted as some distance between bars “on-center”, or from center-line to centerline of each reinforcing bar. But how close to this spec does the builder need to get? If it calls for bars to be 12″ on-center, what if you end up at 12.5 or even 13 inches? The acceptable tolerances for reinforcing bars are specified in the governing building code known as ACI 318, Building Code Requirments for Structural Concrete, which is adopted by reference in the IBC model code and all state codes which adopt the IBC.

Reinforcing Bar Tolerances

There are normally 3 dimensions specified on structural plans that that must be taken into consideration when placing reinforcing steel and two of the dimensions have Code specified tolerances. The 3 dimensions normally stated are:

  1. Size and spacing – for example #3s @ 6” O.C.
  2. Clearance from steel to earth, usually 3” for concrete or shotcrete cast directly against earth.
  3. “d” distance which is the thickness of concrete or shotcrete from the steel to (in engineer jargon) the compressive face of the structure. On normal pool designs, this is the thickness of shotcrete from the steel to the face of the shotcrete closest to the water. On free-standing pool walls there is actually a “d1” and a “d2”. “d1” is the same as “d” or the thickness of shotcrete from the steel to the face of the shotcrete closest to the water. “d2” is the distance that the re-bar must be blocked from the earth in accordance with the pool engineering tables.

1907.5.2.2 Tolerance for longitudinal location of bends and ends of reinforcement shall be ± 2-inches.

1907.6.5 In walls and slabs other than concrete joist construction, primary flexural reinforcement shall not be spaced farther apart than three times the wall or slab thickness, or 18 inches (457 mm).

1907.5.2.1 Tolerance for depth d, and minimum concrete cover in flexural members, walls and compression members shall be as follows: