Warehouse Slab Design - Dowel-less joints

[Boiler106]

We have a warehouse with light forklift traffic and a Contractor that has a lot of experience and success with placing 6 inch slabs, unreinforced and control joints at 12.5' oc without dowels with other engineers.

I'm fine with the plain concrete and joint spacing, but in my experience, I've always provided dowels for load transfer with wheeled traffic.

For the life of me, i cant find a reference for eliminating dowels for this type of loading. Does anyone have a reference or any helpful hints?

 

[WARose]

You'd have to check your load near an edge (with construction joints). That winds up controlling for a lot of slab on grade designs. (That and corners.)

 

[spieng89]

I've ran into issue where the edges on slabs where no dowels were used started to curl i.e. shrinkage and the gap between the slabs would start to increase past the designed control joint width. The control joint would crack as designed, but due to various factors the shrinkage of the concrete pulled the slabs apart. It wasn't a strength issue, but definitely didn't look good

 

[racookpe1978]

Forklifts are characterized by small, very hard wheels and a high center-of-gravity driven all too often by nitwits (er, low-skilled, high testosterone young employees) carrying valuable loads in a warehouse surrounded by many near-by targets (er, other people and racks).

You do really need to keep the slab offsets to an absolute minimum. That other warehouses didn't report problems when the owner took over from the construction contractor doesn't mean there are no problems now, in the future, or problems that aren't reported from the forklift operators to the forklift foremen to any forklift supervisors to any previous operating managers to any previous executive officers to any previous owners back to this particular contractor, who wants to report to you that "there have been no problems in previous jobs".

That's a lot of filters between the guys who have to slow down at each joint and the contractor who doesn't want to put in dowels.

 

[JAE]

surrounded by many near-by targets (er, other people and racks)

Don't forget about the building columns. Forklift drivers LOVE to hit those!

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[MotorCity]

Dowels are typically not used at control joints, as there is no purpose for load transfer. The intent is for the concrete to crack at the control joint, and any reinforcing in the slab may or may not continue through the control joint. Dowels are required at construction joints where you have a cold joint through the entire slab thickness, thus you need some method to transfer load across the joint (shear key, dowel, or both).

 

[Boiler106]

@Motorcity, incorrect. Dowels are not usually needed in slabs using stationary loads at control joints. They are often used on slabs using wheel loads.

 

[MotorCity]

Boiler106, I think we are saying the same thing. Reread my first statement "Dowels are not typically used at control joints". The use of dowels should not depend on the type of load (stationary vs. static). I provide dowels based on the magnitude of the load and the need to transfer load across a construction joint.

 

[hokie66]

I think you should just admit that you are wrong, MotorCity. No shame in that.

 

[civeng80]

No Dowels ? So a keyed joint ? Something they used years ago, probably as effective as dowelled joints IMHO.

 

[hokie66]

keyed joints are prone to breaking off the outside part when forklift wheels pass over. Thus the reason that centrally located dowels are better. Diamond plate dowels and square dowels with compressible material on the sides are better, as they allow for shrinkage parallel to the joint. Whatever kind of dowel is used, it is essential that they are normal to the joint.

 

[MotorCity]

hokie66, what part(s) of my statement do you believe to be incorrect?

 

[Boiler106]

@civeng80 - no, we're talking sawcut control joints and diamond plate dowels at the construction joints. No keys.

@MotorCity - dowels are provided at control joints for load transfer in slabs subjected to wheel loads. Refer to the Army Manual CONCRETE FLOOR SLABS ON GRADE SUBJECTED TO HEAVY LOADS pg 5-12 fig 5-6 and ACI 360R-10 figure 6.5.

http://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/tm5_809_12.pdf

I've since come across "aggregate interlock" in ACI360. Does anyone have experience with this?

 

[hokie66]

MotorCity,

The statement which is incorrect is your opinion that dowels are only used at construction joints, not control joints. This is clearly inaccurate in industrial slabs, which need a better mechanism than aggregate interlock.

All that said, I think joints in slabs at 12.5' centres will soon be a thing of the past. "Jointless" slabs are being used more and more. The main advantage is in reducing maintenance costs.

http://northrop.com.au/201704/big-pour-australias-largest-joint-less-concrete-slab-port

 

[civeng80]

hokie

TNT would disagree with fibre reinforced pavements.

 

[hokie66]

You will have to explain that. A project that went wrong, perhaps?

 

[bones206]

One of my firm's clients mentioned a facility of theirs that was constructed with a jointless slab using "Teqton". Link

 

[MotorCity]

hokie66, contrary to your experience I have done countless industrial slabs w/ heavy uniform loads and forktruck traffic and cannot recall placing dowels at control joints. Have not received any complaints from owners or contractors. I must be in the minority of engineers described by the OP. We've done unreinforced, reinforced, and fiber reinforced slabs this way. For unreinforced slabs, load transfer is not an issue since the loads are usually small and/or the base is very good. For reinforced slabs, we place a layer of bars at mid depth and continue those bars across the control joint. If/when the slab cracks, the reinforcing across the joint transfer the load and prevent the crack from widening.

 

[WARose]

[blue](MotorCity)[/blue]

I have done countless industrial slabs w/ heavy uniform loads and forktruck traffic and cannot recall placing dowels at control joints.

Me either. The only time I use dowels is at construction joints.

 

[SlideRuleEra]

There has been no mention of the subgrade or it's preparation. To me, that is the "wild card".

If subgrade is "good" and correctly prepared... plain concrete, with or without dowels, will likely work just fine.

Or, as with most of my projects, if subgrade material is a "compromise" (but well prepared), even reinforced slabs, with dowels everywhere can have a hard life.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net