What is a cracked slab?

Cracked slab – What is it and why this term is misleading

Why the term cracked slab is misleading

The term “cracked slab” is not a technical term.You will not find it in any engineering text we are familiar with.

The term “cracked slab” is used by lay people and foundation repair contractors.I frankly do not like the term and believe it should not be used.Language can be used in a way that helps us understand and solve problems and language can be used to obscure and confuse.In my opinion, the term “cracked slab” serves no legitimate purpose.

Why all slab-on-ground foundations are cracked

The term “cracked slab” can be understood literally to mean a slab that has cracks.But if this is what term is taken to mean, then it conveys no useful information at all. All concrete exhibits cracking. It is a characteristic of the material that it cracks. There is, in fact, no difference between a “cracked slab” and a “concrete slab” since all concrete slabs have cracks.

Failure is a misleading term when applied to a slab-on-ground foundation

Normally, in the structural engineering community, when we talk about a structure failing we see failure as the structure breaking, collapsing and falling down.

This concept of structural failure applies to elevated structures, like bridges. Bridges can collapse and fall to the ground.

Slab-on-ground foundations cannot fail in that sense. They are not elevated; they are ground-supported. Since they are on the ground, it is not possible for them to collapse and fall down.

A better way to think about slab on ground foundation performance

Slab-on-ground foundations are most realistically understood and evaluated, not in terms of “failed” or “not failed”, but in terms of performance, specifically in terms of degrees of performance.

To quote Donald P. Coduto, P.E.

A common misconception, even among some engineers, is that foundations are either perfectly rigid and unyielding, or they completely incapable of supporting the necessary loads and fail catastrophically.  This ‘it’s either black or white’ perspective is easy to comprehend, but it is not correct. All … foundations have have varying degrees of performance that we might think of as various shades of gray.”  (Foundation Design – Principles and Practices, by Donald P. Coduto, P.E., page 10).

The term “cracked slab” presumes that slab-on-ground foundations are best understood and evaluated in terms of “failed” and “not failed.” This perspective to be wrong and misleading.

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