Defining Foundation Failure in Mid-Size Buildings

A mid-size building is defined as single or multi-family residential, commercial, office, or industrial space not over 3 stories in height and of any lateral extent. This paper will address a definition of foundation failure in terms of the effect on the supported structure based on deformation criteria as opposed to physical damage to the foundation. A foundation is often deemed failed based on the opinion of the occupants, experts or laymen on a jury, often with statements such as "The slab has cracked, therefore the foundation must have failed." This paper attempts to answer the question, "When has a foundation failed and when is it still performing its function?" A concise review of published deformation criteria for different types of structures, ways of measuring and calculating the deformation ratios, and theoretical analysis of material tensile cracking will be presented. New methods are proposed for analysis of curvature of foundation surfaces and for quantifying distress levels to the super-structure. This information will be useful for forensic engineering studies to establish in a practical and in a legal sense when a foundation has "failed", utilizing objective criteria.