Page 174 - Forensic Structural Engineering Handbook

THE FIRST STEPS AFTER A FAILURE 5.7

FIGURE 5.4 Bracing and shoring were installed to prevent further collapse of this parking
deck in Queens, NY.

PRESERVATION OF PERISHABLE EVIDENCE

After a collapse, the position and condition of the structure become evidence. This evidence
will play a crucial role in assisting to determine the most likely cause of the failure and the
contributing factors. Some of this evidence is durable and will remain reasonably intact over
a period of time, possibly even if left exposed to the elements. Other evidence, however, is
of a perishable nature, and therefore must be quickly documented or otherwise preserved.

Collapse Configuration

The collapse configuration can provide valuable information about possible collapse mech-
anisms and the origin of the failure, and may also serve to eliminate some mechanisms from
further consideration. Due to the pressure of various emergency activities, it is likely that
the collapse components will need to be disturbed—or even altogether removed—within a
short amount of time. It is therefore important that the configuration of the collapse be “captured”
as quickly as possible.
It is extremely valuable to establish a nomenclature for labeling key components prior
to their movement and/or removal from the site. Wherever possible, it is desirable to make
use of a predefined nomenclature, such as column grid lines, supplementing it as required.
In some cases, it is necessary to develop the entire nomenclature. This is necessary, if draw-
ings are not available or if the structure is composed of interchangeable elements, such as
a scaffold or shoring system.
If labeling of key components cannot be done prior to their removal, as might be the
case when a rescue operation is underway or if access is hazardous, the components will
have to be labeled as they are removed. This requires closely monitoring the removal oper-
ation, tracking components as they are moved, and labeling them as soon as they reach an
accessible location (Figs. 5.5 and 5.6). This operation will usually require a team of two or