Page 206 - Forensic Structural Engineering Handbook

6.8 ENGINEERING RESPONSE TO FAILURES

FIGURE 6.5 Sometimes load paths are not immediately obvious, making it difficult to ascer-
tain the likelihood of further collapse.

structure? What is the general layout of the pieces and what type of individual component
failures seem prevalent? Who is in control of the site? What permission is needed to access
the site to undertake the investigation? Is the failure interrupting the normal operations of
adjacent properties or public infrastructure?
Often engineers are called in to investigate structures that have not collapsed but are
showing signs of distress. One must determine if the structure is currently stable and able
to carry all or part of the intended loads.
The next step is developing a plan to document the failure condition of the structure.
Photographs of the overall site as well as detailed photographs of critical elements should
be taken (Fig. 6.6). A system identifying locations and piece numbering should be devel-
oped and strictly followed (Fig. 6.7). Common field activities that require recording are
given in Table 6.4.
Documentation of the changing site conditions is often a long, drawn out, painful, and
critical undertaking. There is no substitute for accurate documentation via photos, video,
drawings, measurements, notes, and personal observations. Realize that this effort will be
undertaken in the field in less than optimal conditions (Fig. 6.8).
Since there are often many interested parties and a number of engineering experts
involved, it is typically necessary to agree to a protocol for evidence documentation, con-
trol, and testing. This protocol should be negotiated as quickly as possible. It should address
a chain of custody and any potential spoliation issues.
It will typically be necessary to return to the field on a continuing basis; both as material
is removed, as new evidence is uncovered, and as document review, structural analysis, and
testing indicate areas of particular interest.
Ultimately in-situ load testing may be necessary to determine the actual structural
capacity of any remaining structure. This information can be used to verify the failure sce-
nario or in the process of returning the structure to service (Fig. 6.9).