Monolithic slab-on-grade joints
Monolithic slab-on-grade joints
(OP)
I am interested in how other engineers detail their monolithic grade beam/slab-on-grade foundations. I am in a highly expansive clay region and I design my foundations using the WRI method. How do you limit cracking for your monolithic foundations? Sawcut contraction joints would be what I would typically use for a slab-on-grade application if I was not on expansive soil, but it seems this contradicts the idea of a monolithic foundation. ACI 360R-06 recommends a minimum steel ratio of .5% of the slab cross-sectional area in order to eliminate sawcut contraction joints. For a 4" deep slab that would put me at needing 0.24 in2/ft of reinforcement (#4 bars @ 10" o.c.). This seems real high. Any thoughts would be appreciated.






RE: Monolithic slab-on-grade joints
RE: Monolithic slab-on-grade joints
For crack control on a foundation where I was not overly concerned about soil movement, I would typically use sawcut joints and discontinue a portion of the reinforcement at the joint. I don't think this method would be good for stiffened foundations that have been designed with the anticipation of soil movement.
How do you detail joints for a stiffened foundation? How do you lay them out? Similar to the example in the attached file?
RE: Monolithic slab-on-grade joints
As for our topic, I would refer you to a book called Designing Floor Slabs on Grade: Step-By-Step Procedures, Sample Solutions, and Commentary it was very helpful to me.
I have to go, but if you still need additional information, let me know and I'll find the methods suggested in the book.
RE: Monolithic slab-on-grade joints
I appreciate your input and I will check out that book.
RE: Monolithic slab-on-grade joints
Removing 7' of expansive material below and out from the building sounds like a solution, and I suppose in your area it may be economical. In other areas, I suggest a deep foundation with void formers under the slab would be preferred.
As to joints, your slab is either a stiff raft or it's not. Sawing joints in a raft makes no sense.