Page 327 - Forensic Structural Engineering Handbook

10.16 CAUSES OF FAILURES

To be sure, one can use the ASCE-7 Minimum Design Loads on Building and Other
Structures, the AISC Specifications for the Design of Structural Steel Buildings, the ACI
318 Building Code Requirements for Concrete, the NFPA National Design Specifications
for wood, and other well-known documents to determine loads and allowable or ultimate
stresses in the design of temporary structures. But those design loads and design stresses
were not established with the conditions of temporary works in mind. Therefore, they may
not be the most appropriate for temporary works, to which not only strength and service-
ability but a gamut of other criteria as well have to be applied as is apparent from reading
the section Understanding the Design-Construction Process in this chapter.
As mentioned earlier, for bridges, the FHWA document: Guide Design Specifications
6
for Bridge Temporary Works is a valuable guide.

CASE HISTORIES OF TEMPORARY
STRUCTURES FAILURES

Construction failures caused by defective performance or complete absence of temporary
structures in construction is an almost daily occurrence. Just about every step along the
design-construction process includes hidden risks and has been shown to be prone to errors
or omissions that result in subsequent construction failure. Failures of excavation supports,
scaffolding, falsework, formwork, and temporary shoring, bracing, and guying (in approx-
imately this order) are the most frequent occurrences of temporary structure failures. Often
the total absence of some of these—such as excavation supports, shoring, bracing, and guying—
is the proximate cause of a disaster.
With very few exceptions that involve large fatalities, temporary structure failures do
not make as much news as the collapse of a building or bridge. They may happen away
from the public eye, at an isolated construction site, or behind solid fences, and they are
often kept hidden—for everyone’s benefit. The author has observed that whenever a con-
struction failure is reported in ENR, Engineering News-Record, in books, or in other tech-
nical publications, it is nearly always the permanent structure that is described, with little
or no discussion of the details of the temporary structure even if it was the thing that actu-
ally failed.
It is the author’s opinion that almost always one of three reasons is the underlying cause
of all temporary structure failures: one is the willingness, indeed deliberate choice, to
accept greater risks; another is error or omission out of oversight, carelessness, or igno-
rance; and the third is an unanticipated confluence of events or conditions. All are human
failings and all can be averted. Therefore—at the risk of being simplistic—failures can be
prevented.
An interesting fallout from failures and their investigations is that regardless of what is
found to have been the proximate cause of the failure, and who is found to have the imme-
diate responsibility, often several other errors or defects related or unrelated to the cause of
the failure are discovered as well, which might never have come to light if not for the failure.
If you scratch hard enough, you will find many problems and several culprits—often more
than first meet the eye.
It is believed by some that the best way to learn how to prevent future failures is by
studying past failures. In this author’s opinion such studying is often superficial and largely
useless unless one delves really deeply into the design and construction details of the pro-
ject. Few construction failures are so simple that all the pertinent information can be dis-
cussed adequately in a paragraph, in a page, or even in two or three pages. Nevertheless,
for the sake of illustration of the extent of temporary structure failures, and at the risk of