Concrete Tension lap splices

[jreep1973]

In Class B tension lap splices; why is there another 1.3 splice increase for "top" bars?

 

[sandman21]

The increase for "top" bars, comes from ACI 318-08 12.2.4(a). However it applies to both splice types when more than 12" of concrete is placed below the bar. The factor is to account for air bubbles that form around the reinforcing.

 

[jreep1973]

Sandman21 - Thank you for your post!

 

[hokie66]

The factor is to allow for incomplete compaction, and as sandman pointed out, voids around the bars. The incomplete compaction is due to plastic settlement. Plastic settlement can be dealt with by revibration, but the splice increase is in recognition that construction practices are not always good enough.

 

[Guastavino]

Going from memory here but doesn't it also have to do with large aggregate settling to bottom of beams too?

 

[sandman21]

Bottom bars would not have 12" of concrete placed below so they would not need the extended splice.