Clear Spacing between rebar layers

[jeffstevens]

Hello All,

New to this forum, but I have a question about the clear spacing between bars. For the purposes of calculating development length, ACI318-11 12.2.2 allows you to use the reduced value if the clear spacing between bars is at least twice the bar diameter. Does this spacing restriction apply in the vertical direction between layers as well as in the horizontal direction?

It seems like it would based on the language of the commentary and table, but the commentary makes specific reference to 7.6.1 (the section on horizontal clear spacing) without mentioning 7.6.2 (the section on vertical spacing). Thanks.

Jeff

 

[TXStructural]

The clear distance is for two principle purposes: 1) to assure that good consolidation around the bars is possible, and 2) to be sure there is sufficient concrete around bars to provide confinement using the tension capacity of the concrete. In this case you mention, I would not be concerned about having sufficient confining concrete, but would be concerned about reduced consolidation. Where bars are too close together, you can end of with only concrete paste between bars (uneven distribution of large aggregate) with the end result of easier tension cracking along the bars and potential for shrinkage cracks as the paste cures and shrinks.

 

[bb29510]

1 1/2 times the larger aggregate

 

[Ron]

As given in ACI 117 (Tolerances)....

2.2.4 Distance between reinforcement:
One-quarter specified distance not to exceed
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 in.
Providing that distance between reinforcement shall not be less than the greater of the bar diameter or 1 in. for unbundled bars.