Page 181 - Forensic Structural Engineering Handbook

5.14 ENGINEERING RESPONSE TO FAILURES

5. Weigh the contents, and measure the opening of the container used. The results can then
be reported in terms of pounds per square foot.
Depending on the consistency of the snow, it may be possible to remove the inverted
container and leave the snow standing. Measurements of the thickness of snow and ice
strata could then be made before placing the material in the container for weighing.
If possible, several samples should be taken from each selected location to minimize
random measurement errors. It is also recommended that the measurement process be
videotaped, or at least extensively photographed.

RESERVING SAMPLES

Except for the smallest of failures, it is usually impractical and unnecessary to reserve the
entire structure. The forensic engineer will usually have to make decisions regarding what
portions of the structure should be set aside for future use. It is important that the forensic
engineer be present during demolition, so he or she has the opportunity to identify addi-
tional components, as they are uncovered.
It is important that a chain of custody for all samples be maintained in the event that the
matter eventual goes to trial.

Failed Components
Failed components are obvious candidates for preserving. Most important are failed items
that are suspected of being associated with the initiation or propagation of the failure, as
opposed to items that failed due to consequential impact. However, in the early stages of
an investigation it is not always possible to distinguish initiation damage from consequen-
tial damage with any degree of certainty, so it may be prudent to retain all damaged ele-
ments. (See Fig. 5.11.)
Unfailed Components

Unfailed components can be useful for several purposes:
• For use in a testing program. Care must be taken to ensure that the selected sample was
not materially damaged in the collapse, if the results are to be used as a basis for esti-
mating the strength of similar failed components.
• To study its construction.
• To study differences between it and companion failed components.
• To exemplify to audiences, particularly nontechnical persons, what a typical unfailed
component looks like or how it functions.
• To conclusively show that a certain component did not fail.

DOCUMENTATION OF CONDITIONS

High-quality documentation of the existing conditions is invaluable for developing
hypotheses—as well as for ruling them out—and for ensuring that collapse theories are
consistent with the physical evidence.
Various methods can be used to document conditions, including field notes, pho-
tographs, video, and new technology.