Expansion Joint In Mat Foundation

ACI 318-11

I agree that the size of this mat foundation is impressive. There are several things to consider here. The temperature extremes are impressive. Will this temperature range be the same whether inside or outside the building? The floor of an enclosed building with a cool roof won't vary very much. In any case the contraction or shrinkage of the curing concrete slab will exceed the amount of heat expansion in the concrete during the hot times. Usually large slabs must be provided with contrction joints to accomodate the cure shrinkage rather than to provide room for expansion. Reinforcing steel must be installed in a grid form in the concrete to disperse the stresses from the cure shrinkage. If a two foot grid using #4 rebar is selected the actual shrinkage within the two foot by two foot will be localized as a very small part of the total shrinkage of the whole slab. In effect the rebar grid will keep the slab from shrinking and cracking. Since a mat foundation will need to be reinforced with steel rebar to distribute the weight of the buildng over the entire area the mat foundation covers. That reinforcing system will probably be sufficient to control the shrinkage and keep the concrete in one piece.

Adding to "Too Cool" answer; please ensure the CG of the super structure loads is within the 1/3 of the foundation (Mat foundation here) CG line as a general rule in both axes. ACI does not specifically lays out standards / conditions for expansion joints in mat foundation for your case (at least not that I know of); If I am the designer I will NOT go for expansion joints in Mat foundation of 30x40m; since there is no basement you may end-up with leaks and water ingress in future. Further, you may have a pore-pressure issue that may have overturning effect on the foundation (I dont know of the WT level there). Also, I advice you to get a comprehensive geotechnical investigation carried out by a good geo-consultant for this site and let us know of the geo consultant's views on expansion joint in the mat foundation of this structure.