Page 293 - Forensic Structural Engineering Handbook

9.4 CAUSES OF FAILURES

DEFECTS AND DETERIORATION

A routine condition assessment of an existing structure may be performed for a number of
reasons, including (but not limited to) determining whether a structure is safe for public
occupancy; establishing code compliance or determining areas of noncompliance to be
remedied; and determining the cause and appropriate remedy for problems that elicit owner
complaints such as leaks, movement, floor vibrations, or trip hazards. A forensic investiga-
tion (related to dispute resolution, such as litigation) may be similar to one of these condi-
tion assessments, except that the study would be expected to be more formal and thorough.

Causation Theory
In forensic investigations, various tasks are performed (such as fieldwork) to identify devi-
ations, degradation factors, defects, deterioration, distress, and failures that exist(ed) in a
facility. To prove a causal relationship between these items (i.e., to prove that the identified
conditions caused the failure), it is essential to determine the following three elements,
which like the legs of a three-legged stool, all are necessary to support a causation theory:
• Pervasiveness: How widespread the conditions are in the facility. From random sampling
to comprehensive observations, various techniques are available to quantify pervasive-
ness in a manner that will stand up to adversarial scrutiny.
• Severity: The significance or consequences of the conditions. For example, some defects
and deterioration are minor, so it is not sufficient simply to identify them as present
unless they can impair performance.
• Proximate cause: The most significant factor(s) deemed to produce a specific effect.
Although the proximate cause of some failures may be procedural, this chapter focuses
on a subset: failure mechanisms related to defects and deterioration.

Defects
Defects are often categorized as originating during design, manufacturing, fabrication, or
initial construction; therefore, they are typically present at the beginning of the service life
of a structure. Latent defects are those that are present during initial construction but lie dor-
mant prior to manifesting themselves; they are commonly understood not to be detectable
until later in the service life of a building (the Latin origin of latent means “to lie hidden”)
because of both concealment and dormancy. The converse, a patent defect, is readily open
to observation—something that is evident and obvious (the Latin origin of patent means
“standing wide open”).
This section outlines three categories of defects (whether latent or patent): design
defects, product defects, and construction defects.

Design Defects. In professional engineering design offices, it is common practice for
designs to be peer reviewed, and many design errors are “caught” by this process. However,
defects in design still occur due to poor detailing, insufficient detailing, or a lack of atten-
tion to constructability of details.
There is also occasional abdication of design responsibility that transcends errors or
omissions. For example, it is common engineering practice to show on structural details the
size and position of shelf angles to support brick masonry veneer, but only to indicate the
masonry by a phantom line, implying that the masonry itself is trivial to the engineer. A