Maximum plan dimensions for slab on grade 2

[mar2805]

Hi folks!
What are maximum plan dimensions of a 4" thick slab on grade that will not crack due to shrinking problem?

I can use a "drag formula" for 1-layer reinforced SOG, but what aboth unreinforced slab?
Is it safe to put an very very small value of reinforcement area in the drag formula and calculate joint spacing?
Thank you.

 

[mar2805]

Guys, for your answer on joints, provide joints "36 times the slab thickness and not greater then 15 feet".
My question is, with how much reinforcement is this statement vaild?
I found an article wich describes 5 methods for providing reinforcement in slabs on grade. (attach)
"Subgrade drag procedure" gave always the minimum percentage of reinforcement (aboth 8 times less)
Why such a drastic difference, if the reinforcement is considered as non-structural !?!

 

[n93s412]

Maybe you are conflating "shrinkage and temperature steel" and "structural steel". More shrinkage and temperature steel is required in SOG applications because shrinkage and temperature has a more dominant affect than in an exposed structural slab where there is less restraint to movements caused by shrinkage and temperature.

 

[mar2805]

Im sorry, but I dont understand you...

 

[n93s412]

Slabs-on-ground may require more shrinkage and temperature steel than a overhead structural slab due to the slab-on-ground being more restrained from movements due to shrinkage and temp.(i.e. curling).

 

[mar2805]

I dont think youre right.
SOG are restrained only on the bottom side since this part is in contact with soil and friction develops.
Suspended slabs are cast in formwork wich on the bottom sides also couses friction + slab is connected sideways with reinforcing bars with other elements such as walls, beams...

 

[n93s412]

ACI 350 requires two to three times the amount of steel for members subjected to environmental exposure conditions (depending on the distance between movement joints) as compared to ACI 318 minimum temperature and shrinkage steel for elevated slabs (0.18%).

 

[n93s412]

just for a fun fact of the day...not in response to your last post