correct column tie spacing

[techmaximus]

I have been inspecting rebar and PT installations for over a decade and I have the ICC Reinforced Concrete Special Inspector certificate. I have previously worked for a premier structural engineer in the SE as shop drawing review and field inspection. Now I work for a testing lab doing primarily field inspection work. Even with all of my experience there are a number of things about rebar installation and drawings that bug me and I want to ask you structural guys and gals about them. For instance…..

Column Tie Spacing for multi Story Building (read from bottom up)

2 ties Equally Spaced in Beam
Bottom of Beam
1 tie at 4”
3 spaces at 8”
Remained at 16”
3 spaces at 8”
1 tie at 4”
Top of Slab-on-Grade

Columns are “pre-tied” horizontally on a rack on the ground. The rodbuster starts the spacing at the bottom of the column and works his way to the top. The columns are later set with the crane.

Here is my problem: once concrete is placed in the form and the form is subsequently removed I should only be able to observe TWO ties. The only TWO ties that I should be able to observe are the two ties that the rodbuster has tied on the dowels (for convenience) that are later to be equally spaced in the depth of the beam.

It is my contention that if I observe more than two ties that the required tie spacing is incorrect and steps must be taken to correct the discrepancy. The contractor has poured a number of ground level columns and I can observe THREE ties on a number of them. To me this means that the one tie required at 4” below the bottom of the beam is missing and that the next tie down could be as much as 8” below the bottom of the beam. Any columns on which I can observe 3 ties have two spaces at 8”, are missing the 1 at 4” and will have 3 in the beam.

The contractor claims (wrong headedly) that the spacing is determined by starting at the bottom of the column and working up and that a tie at 4” below the bottom of the beam may or may not occur as the beam depths vary. What!? I understand that the beam depth will affect the TOTAL number of ties on a column but the spacing should not be affected unless a beam depth not divisible by 4” was introduced.

It is my opinion that upon standing the column rebar that the layout engineer should shoot the bottom of beam elevation and determine if that one tie is going to be at 4” below bottom of beam or not and if not that the ties be adjusted until the spacing is correct.

Am I nit picking this guy as he vociferously claims or should I bring this to the attention of the engineer of record?



SCET - Techmaximus

 

[JAE]

I vociferously claim you should bring this up to the EOR. It is my guess, though, that the unequal spacing of the ties is due to a requirement of the EOR to have a particular shear capacity in the column, based on some kind of shear distribution in the column (which I cannot fathom at the moment - but he is the EOR).

With that, the 4" spacing is presumed to occur in the column, just below the beam. There are requirements in high seismic areas for particular amounts of ties within the beam/column intersection. But clarification from the EOR is the proper thing to do here, and it would also allow both you and the contractor to defer to that source and not be at each other's throats.

 

[techmaximus]

Although I’m sure he wanted to ring my neck over this and some other deficiencies I wrote up, we never really got at each others throats. The EOR did straighten him out on this matter. My point all along was that if the tie required at 4” below the bottom of the beam was too high it was often high enough to be in the bottom of the intersecting beam. The tie spacing doesn’t have to be perfect but the column ties should at least be in the columns and not in the beams. Apparently very few inspectors look for these ties after a column is poured but I find it interesting to see if they are getting this correct.

Techmaximus

 

[LdsUtd]

The easiest thing to do is to observe the tied and formed column when it is in its upright position, but not poured yet. You can observe the ties, and if they are at proper spacing. You can see if they have the extra tie at the top and bottom, etc. The key here is to make sure the top of column is marked on the formwork so you can see where the tie spacing should start.

You can either make sure they leave off one side of the formwork on a couple columns, or climb a ladder and observe it.

In your case, yes it sounds like you should only see the 2 ties in the beam, and the tie 4" below the bottom of beam definitely needs to be 4" below bottom of beam.

What did the EOR have the contractor do?