Page 190 - Forensic Structural Engineering Handbook

THE FIRST STEPS AFTER A FAILURE 5.23

suggest lines of questioning. The forensic engineer can also assist by identifying types of
persons to focus on. The forensic engineer and the interviewer will need to be in constant
communication, so that the forensic engineer can make use of the statements, and so that
the interviewer’s lines of questioning can be updated. In some instances, the forensic engi-
neer may suggest follow-up questions for a particular individual, or may feel that he or she
should attend a follow-up interview.

Information Sought

Although the specific information that is sought from interviewees will depend on the par-
ticular project, certain lines of questioning are common to nearly all types of failures:
1. Status of construction at time of collapse. If the collapse involves a structure under
construction, the forensic engineer will probably need to determine the status of the
construction. Was the bracing in place yet? Which connections were complete or
incomplete? Which slabs were in-place? Which had been reshored? What was the status
of the underpinning work?
Bearing in mind that the interviewee may have incomplete knowledge about the con-
struction, responses should be compared against other accounts and against physical
evidence.
2. Sequence of collapse. Knowing which element, or which area of the structure, was the first
to fail could help to quickly focus the investigation. However, an individual’s perception
of the sequence will depend on many factors, such as the speed of the collapse, where he
or she was, what he or she was doing, what drew his or her attention to it, and so on. It is
rare that a single individual’s perception of the sequence will be fully accurate or provide
the complete picture. In all likelihood, it will be necessary to piece together the various
accounts into a coherent sequence, weighing the reliability of each account. Wherever
possible, physical evidence should be sought to confirm or deny accounts.
3. Possible triggering events. Most collapses have a triggering event associated with them,
and identifying it may speed the investigation. Sometimes the trigger is conspicuous,
like an errant barge striking a bridge pier; other times it is subtle, such as one more ther-
mal cycle in a fatigue-critical member. (See Fig. 5.18.)
a. Activities underway at the time of the collapse. In the case of a structure under con-
struction or renovation, it will be important to identify exactly what was being done
at the time of the collapse. Was a bracing member being temporarily disconnected?
Was concrete being placed and, if so, exactly where? Were workmen in the process
of plumbing the structure? Persons associated with the project will be the most useful
in this regard.
b. Unusual loading on structure. Was there a collision or other unexpected impact?
Was the structure overloaded by storage of construction materials? Was the occu-
pancy loading unusually high? Eyewitnesses will often be able to offer some insight
into these questions.
c. Environmental factors. High winds, snowfall, and other unusual weather-related
patterns are possible triggering events of a failure. Persons present at the site should
be able to provide a sense of the role that environmental factors may have played,
which can be quantified through the review of climatalogical data.
Table 5.1 includes typical questions, as well as information that should be included
with each typed transcript or summary. The list should be tailored to suit a specific pro-
ject. It may also be useful to develop different lines of questioning for different types of
interviewees. For example, when interviewing employees of a concrete subcontractor it