Staggering Lap Splices

[bones206]

I brought up this question at work and got different answers.

When lap splices are required to be staggered by a certain distance (say 30"), is that distance measured from the center of the splice to the center of the adjacent splice? Or is it the clear distance between the splices, i.e. measured from the end of one bar to the start of the bar in the adjacent splice?

I believe that it is the latter, but I can't seem to get a definitive answer. For a mechanical splice, it is fairly obvious that the stagger distance would be measured center to center. I'm interested to get other people's opinions on this.

P.S. the lap joints at our jobsite have already been installed using 30" center to center staggering.

 

[ishvaaag]

As per the spanish code EHE, center to center.

 

[bones206]

Thank you Ishvaag.

So per Spanish code, you are allowed to have adjacent splices thru a section...

One argument I heard is that this condition is not desirable because it promotes cracking along that section.

 

[BAretired]

I agree with the Spanish code. To stagger items a distance 'x', alternate items are moved a distance 'x' which is the same as center to center.

BA

 

[ron9876]

If it is a column where the stagger is intended to reduce congestion typically place one splice at the foundation and the other at mid-height. But at least such that the lap bars don't occur at the same location.

 

[bones206]

Here is a sketch. This situation is generic and could apply to a column, beam, slab, wall, etc.

I still think that splicing the bars in the same plane potentially creates a weak point in the structure. Isn't this the idea behind staggering mechanical splices?

In NRC Reg. Guide 1-136 Revision 2 (1981), Position 9 states:

Mechanical splices are considered to be weak links in the performance of reinforcing bars. Thus, staggering of mechanical splices in areas of high stress is being reemphasized in order to avoid a concentration of splices on one plane in such areas that may result in (1) unacceptable cracking and (2) increased steel congestion that has adverse effects on concrete placement. In addition, this recommendation is consistent with ACT 349-76, "Code Requirements for Nuclear Safety-Related Concrete Structures."

In Revision 3 (2007), Position 8 states:

Mechanical splices located in areas of high stresses (maximum computed tensile stress ?0.5 Fy)
should have alternate bars spliced or adjacent splices staggered. If tests for slip (or internal plastic
deformation) of the splice demonstrate that the slip is low (i.e., not to exceed 50% of the elongation
of the unspliced bar along the spliced length), at 0.9 Fy, the adjacent splices need not be staggered.

So does this logic extend to non-contact lap splices or are they allowed to overlap across a single plane, since the bond is transferred over a longer length than a mechanical splice?

 

[BAretired]

The second diagram is to be preferred. In that case you would be staggering a distance of (Lap length + x).

BA