CONCRETE SLAB ON GRADE CONTROL JOINTS - SHEAR TRANSFER

[fne]

With the use of steel fiber reinforcing, have people been using dowel baskets to transfer shear across saw cut control joints, or do you believe the aggregate interlock will be sufficient?

 

[msquared48]

Is this a slab on grade, or an elevated slab?

Mike McCann, PE, SE (WA)

 

[fne]

Slab on Grade as noted in the post title.

 

[msquared48]

Missed that. Duh! Sorry.

Mike McCann, PE, SE (WA)

 

[oldestguy]

Concrete may shrink, somewhat dependent on W/C ratio. That may pull your joint more open and affect aggregate in shear.

 

[fne]

Thanks for the interest. Not looking for an explanation of what the mechanism is. Wondering how people are approaching. We are seeing more use of fibers and less of conventional reinforcing. Along with the use of fibers is an increase in joint spacings. Wondering if people are comfortable with the fibers holding the joint together to develop the aggregate interlock or if they feel dowel baskets or other shear transfer mechanisms are needed.

 

[hokie66]

I think the emerging practice is to eliminate all sawn control joints in these "jointless" floors, just leaving construction joints, which do require dowels.

Many of the industrial and commercial projects which minimise jointing are turnkey, using proprietary designs and construction procedures. The materials are all readily available, but not everybody wants to go to the expense of floors which have joints spaced at 30 to 35 metres. Like everything, with time, the costs will come down and the use will become more widespread.

 

[Ron]

Shear transfer by aggregate interlock works with low water cement ratio and proper control joint spacing. Further, use the largest coarse aggregate you can get for the application. That reduces shrinkage, reduces cement content and reduces water requirement.