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Re: IBC Special inspection for Slab-on-Grade supporting HVAC unit.

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Well, to belabor this thread even more, since  most of the answers to the original question were actually wrong,  I thought it was entirely appropriate for the question to be re-asked. 
 
I also think it is worth noting that although the IBC states that structural inspection is not required for a nonstructural concrete slabs supported directly on the ground,  neither the IBC nor ACI define a nonstructural slab-on-ground.   To figure out the presumed intent,  one has to look at the title of ACI 318  "Building Code Requirements for Structural Concrete" and see that ACI 318 does not cover slabs-on-ground unless they transmit vertical loads or lateral forces from other portions of the structure to the soil.   From that one can presumably infer that a slab-on-ground is nonstructural unless it transmits vertical loads or lateral forces from other portions of the structure to the soil.
 
One can try to figure it out from looking at the definition of structural concrete except the IBC and ACI 318 define structural concrete as "Concrete used for structural purposes including plain and reinforced concrete."  ACI 116 defines structural concrete as "Concrete used to carry load."
 
These definitions aren't necessarily consistent.  They are also vague enough that they can be construed differently.
 
Code-writing organizations are increasingly realizing that things need to be clearly defined.  Any thing that is vague can ultimately be defined by a judge or jury in a way that is entirely inconsistent with the code writer's intent.
 
One can certainly argue that stiffened slabs-on-grade designed to resist differential movement are structural slabs or that certain industrial slabs designed for specific wheel loads are structural slabs.  One can argue anything.  However, one of the reasons for having a Code is that these things don't have to be argued.  If you know what the Code requires, you can comply with it, and someone can't later argue that your design is incorrect because it does not comply with the Code.  Your design might be incorrect if it does not comply with the client's requirements for serviceability but this has nothing to do with whether Code requirements for structural slabs apply (which is actually what the question was.)  It should be noted that most stiffened slabs-on-ground designed to resist differential movement are in fact structural because they commonly support a house.
 
One can also argue that a nonstructural slab is not designed for flexure,  but anyone who has actually designed a nonstructural slab might question this.
 
And although common sense is probably necessary for a long and productive life, it is to a large extent a learned property.   If one has not had the opportunity to acquire common sense on a particular topic,  Building Codes serve as a valuable reference.   Building Codes are nominally written by people with expertise in the subject being discussed.   Perhaps even more important,  common sense is often not sufficient to define something.  For example,  how would common sense help you decide that something shorter than 3 ft does not have to be designed as a column?  Why  3 ft rather than 2 ft or 4 ft?
 
Someone with a lot of extra time might wonder why ACI 318 defines structural walls but doesn't define structural slabs.
 
Someone might also be encouraged by the fact that the new and improved next version of ACI 360 has an entire chapter on "Structural Slabs Supporting Building Code Loads."
 
However, the entire chapter consists of the following two paragraphs:
 
 
"CHAPTER 11 - STRUCTURAL SLABS-ON-GROUND SUPPORTING BUILDING CODE LOADS
 
11.1 -Introduction
There are cases where the slab-on-ground transmits vertical loads or lateral forces from other portions of the structure to the soil. For example, storage rack columns can be used to support the building roof, and there are times when a mezzanine is supported only by the slab-on-ground. These structural slabs should be designed in accordance with ACI 318.
 
11.2 - Design considerations
Strength and serviceability are the two main slab-on-ground design considerations. The strength requirements of ACI 318 should be met, however, the serviceability requirements of ACI 318 may not be sufficient for many types of slab-on-ground installations."
 
 
The document does not define either structural slabs or building code loads.

 
Gail Kelley