Joints for flared slab

[Settingsun]

Hi all,
I've got an area of slab on ground with the shape shown below and would like suggestions for joint layout. The area is used for miscellaneous storage and will see some light vehicle traffic (eg 4WD/SUV with trailer). The client (local council) would like to use their standard 150mm (6") thick slab with SL72 mesh reinforcement and dowelled joints. SL72 = 7mm bars @ 200mm each way square mesh (just slightly heavier than 1/4" @ 8"). This is adequate for the loading and subgrade strength. Assuming the 150mm thickness, how would you lay out the joints?

(Imperial: 52' long by 18-32' wide)

Here's a blank version if anyone is enthusiastic enough to sketch.

 

[HTURKAK]

You did not mention if the SOG is interior or not and if the concrete is shrinkage compensating or not..

I will suggest one control joint ( saw cut with depth t/4 ) so divide the length 15.5 m to two parts..

 

[dik]

I'd probably put two joints breaking it up into 5m lengths. The joints would be parallel to the sides until about 3' from the curved part then they would be cut so they were perpendicular to the curve.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

I'd probably go with one of these unless you're stuck with rectilinear jointing for aesthetic reasons etc.

 

[Settingsun]

Thanks, all.

Hturkak, any concern with the length/thickness ratio if only dividing into two parts? The concrete won't be shrinkage compensated, and the slab is outdoors: over the road from a tidal creek and 1.5km from the coast.

Dik, how do you avoid having the lead-in/lead-out scarring the surface where the saw cuts change direction?

Kootk, I think non-rectilinear would look better (at least if you were in a helicopter, not sure about from ground level). I was thinking about your second version except with only two joints breaking up the long edge but wasn't sure whether there are any non-obvious issues, either with performance or construction. Have you done anything like this before?

 

[dik]

You can't... a straight cut is OK if the cut has a large radius.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

Typical contraction joint spacing is 48t which makes in this case 7200 mm . IMO, if you provide vapour barrier PE film and if the SOG is reinforced , dividing into two parts the length (15500 mm) would be OK.


I will suggest you to look ACI 360R-92 .
.

 

[KootK]

Have you done anything like this before?

Yeah, I've done it for lightly trafficked landscaping features. Given my druthers, I'd do it as I've shown below. I'm sure that the reasoning behind it is fairly self evident. If you actually get traffic on that sharp, re-entrant corner, the odds of that cracking off are probably relatively high. A handy feature of interior SOG's is that you rarely actually get traffic loads at the free corners. You might have that same feature here, in effect, if this thing is surrounded by shrubbery or something like that.

 

[dik]

Depending on the radius... maybe the top left one with a straight side cutting off the 'point'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Settingsun]

Thanks all. I've gone with something like KootK's second sketch plus a thickening along the entrance/exit edge.

Hturkak, I didn't see 48*t in ACI360. I have the 2010 version. It has a graph with a range of 3.6-5m for 150mm slab, depending on amount of shrinkage, and a note that past criteria were in the range of 24-36*t.

 

[HTURKAK]

Dear Steve,

The past criteria 24-36*t is for plain concrete SOG. In your case , you are planning to use WWM (7mm bars @ 200mm each way square mesh ).

I have copy and pasted the relevant table ( for plain concrete )

I looked to one of the famous petrochemical company standard and copy and pasted the relevant clause ;

- The contraction joints for slabs on grade shall be provided on centers up to a maximum of
48 times the slab thickness. These joints shall be formed by scoring of the concrete prior to taking its
initial set, or by saw cutting within 12 hours after placing. They shall extend a minimum of one-fourth
the thickness of the slab.
- The construction joints for slabs on grade shall be provided on centers up to a maximum of 5 m


IMO,If 1.5 km from the coast, we can assume the humidity is moderate and with reinforcement and limiting the slump , 48t would be reasonable spacing for contraction joint.