Sawcutting a slab with columns not orthogonally aligned 3

[skeletron]

I'm dealing with a design situation where the supplied parkade column locations are not aligned. See attached sketch. Back-of-the-envelope scale applies. Item is not constructed.

The first row of columns is relatively fine. There are 7 unequal spans.
The second row, however, has six spans and do not line up with the columns along Gridline 1. "Area 1" is concerning. The literature I have read refers to a handful of rules pertaining to column-to-column cuts, rectangular geometry, and appropriate size. However, there are few examples with irregularity such as this one.

Is a triangular shaped panel acceptable and in what conditions? Would it be more accepted to have mid-panel cuts (ie. one between D/E and F/E)? Other tales of interest and experience with specifying sawcutting?

 

[hokie66]

When I was doing this sort of work, I tended to show the crack control joints between columns, not on the column lines. The columns and their footings restrain the slab, so control joints remote from the columns should allow the slab to shrink toward the columns. An advantage is that you don't get the nasty jagged cracking near the columns where the saw blade doesn't reach. As to the spacing of joints, there are various opinions, so will leave that to you.

 

[JLNJ]

I like how you have it, though some of your panels and their aspect ratios look pretty big. I understand that the back-of-napkin scale distorts things a little.

If you want a mid-panel left-and-right-on-the-sketch cut between 2 and 3, I'd be tempted to make it traverse the full width of the building. You don't want a "T" joint where the cut doesn't continue on the other side. God will put a control joint in there if you don't.

If you don't have column boxouts (or if the columns are concrete) you might consider lining the cuts up on the column faces rather than centerlines to avoid the jagged cracks hokie mentions above.

 

[dik]

Use diamond shaped isolation joints at the columns then sawcut to the points of the diamond, and you need more sawcuts... 26' is too far.

Dik

 

[SlideRuleEra]

Is a triangular shaped panel acceptable and in what conditions?

http://www.SlideRuleEra.net

 

[dik]

The only thing to add is to not terminate a sawcut at a sawcut... it should continue through the next panel.

Dik

 

[gte447f]

I would try to avoid triangular panels or other acute angles.

Also, I am not sure that I agree with other posters who are advising against T intersections of control joints. I think if all of the panels are sized similarly, then they will all shrink at a similar rate and the perpendicular crack will develop at the T before a crack will propagate across the T. However, if the panels are more irregularly sized, then maybe a crack could jump across the T before the perpendicular crack developed. To be safe, on paper, I have seen T joints reinforced with a couple of #4x4'-0" rebar placed in the slab on the uncut side of the T as "crack control bars". Not sure if this actually works in practice.

 

[skeletron]

I have diamond cuts around the columns, but forgot to show them on this sketch. So the sawcuts go between the vertices of the diamond cut.

As expected, there are different interpretations with the spacing so I'll mull this over. Considering a transverse cut between 2 and 3 is an option I did not consider until now. Given the large aspect ratio at the ends and the acute triangle, maybe this could help me out. Thanks.

 

[KootK]

Tracked down SRE's reference anyone interested: Link. I can never get my hands on enough of this stuff as I'll I've really had to go on so far is the PCA Slab-on-Ground book.

 

[dik]

Nope... just joking. Thanks Koot and all the best in the New Year.

Dik

 

[dik]

"I have diamond cuts around the columns," I generally use separate pours with flexcel joints.

Dik