Rebar Lapping

[HKuser]

I have two questions about lapping:

1. If lapping rebar to transfer tension force is a non-contact type, why the code does not require longer lap length than the same using contact lapping method? I am thinking that when a rebar is pulling out, ribs of rebar actually is compressing the concrete and spread the compression force at certain angle like 45' to transfer force to another one. In this way, the design lap length should be lesser than actual one, based on the assumption that concrete only transfer compression force, but not tension force.

2. If one T40 rebar is lapped with two T32 rebar to transfer tension force, will there be any deductions for such lapping considering the load transfer efficiency?

Any BS reference for the above questions? Thank you.

 

[KootK]

1) The allowable offset distance (6" in North America) is baked into the cake for the lap length provisions. Longer laps should be designed based on strut an tie principles generally and would indeed result in longer lap lengths as well a demand for transverse reinforcement. Some codes give you other options as well. I believe that the NZ code lets you offset more if you increase your lap by 150% of the offset distance. Someone should fact check me on that however as I've not seen it in a while. Interestingly, a full contact splice will not perform as well as a slightly non-contact splice. This is because the load transfer mechanism goes rebar --> concrete --> rebar in both cases and there's less perimeter available for bond when the bars are in contact. Older codes used to restrict the use of full contact splicing for just this reason.

2) Not that I'm aware of. Lap length would be based on the tension to be transferred and the bond of the smaller bar.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.