Non Contact Splice Laps

[VTAdam]

Can somebody please explain to me the difference between contact splice lap and non-contact splice laps in columns. I have always thought that the vertical steel acts as channels for the force to go through it. In order for the force to transfer to the next rebar, they should be bundled together. However, I have found out that ACI 318 allows non contact. Any insight would be appreciated. Thanks!

 

[TehMightyEngineer]

Aside from the spacing limits there is not much difference. KootK will come in shortly to provide a bunch of sketches on the ideal strut and tie models showing how a non-contact lap splice works using compression struts between the bars.

Here's a nice quick little paper comparing columns with contact and non-contact lap splices.
www.scielo.br/pdf/riem/v1n3/en_03.pdf

About the only actual difference between the two splices is the requirement that bars be held in placing during the pour. I run into this a lot in the shop where I specify lap splicing between bars of difference spacing on center. The guys in the shop will usually add some extra horizontals or something to support all the bars that are left floating. Essentially, provide contact lap splices more for the guys tying the rebar than for strength.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[TehMightyEngineer]

Here's a similar thread from 2 years ago that discussed this, lots of good info:

[URL unfurl="true"]http://www.eng-tips.com/viewthread.cfm?qid=372669[/url]

If memory serves the conclusion was that non-contact lap splices in columns was a normal practice.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[KootK]

KootK will come in shortly to provide a bunch of sketches on the ideal strut and tie models showing how a non-contact lap splice works using compression struts between the bars.

Tempting but I'm sure that I've done this before on a previous thread and I'm not sure that I can muster the energy for a redo. Also, I've kinda lost my mojo in this topic due to recent discussions regarding the non-suitability of non-contact splices for bars out of plane flexurally (stepping CMU retaining walls & bridge pier dowels). Right now, my feelings are:

1) Most columns are so densely reinforced that it's a non-issue.
2) If I had a column with just four 35M verts and all of the laps at a splice were 6" out, I'd be pretty darn concerned about concrete blowout.

I have always thought that the vertical steel acts as channels for the force to go through it. In order for the force to transfer to the next rebar, they should be bundled together.

Code stuff aside, I think that there is a minor flaw in this line of thinking. Whether a splice is full contact or non-contact, the load transfer mechanism always goes rebar --> concrete --> rebar. In fact, a non-contact lap splice will generally perform better than a full contact lap splice because, in a non-contact scenario, each bar gets something closer to a full 360 degree bond with the concrete which is not possible with contact splices. Some old codes actually restricted the use of full contact lap splices for similar reasons.

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.

 

[TehMightyEngineer]

Tempting but I'm sure that I've done this before on a previous thread and I'm not sure that I can muster the energy for a redo.

Haha! Fair enough, I'm just always amazed at your ability to spring up with a detailed strut-and-tie model sketch.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[VTAdam]

Thank you so much; especially KootK. This has been very informative.