Page 314 - Forensic Structural Engineering Handbook

TEMPORARY STRUCTURES IN CONSTRUCTION 10.3

estimates, the direct and indirect cost of construction injuries in this country is more than
$20 billion annually. No one appears to have estimated and published the total value of
property losses in construction failures. These occurrences are not unique to the United
States but are experienced in all other countries as well, especially in those making great
strides in construction fueled by the developing global economy.
Failures of unbraced excavations, scaffolding, falsework, formwork, excavation supports,
and temporary erection shoring, bracing, and guying—in approximately this order—are the
most frequent occurrences of temporary structure failures. Often it is the total absence of
some of these, such as excavation supports, shoring, bracing, or guying, that is the proxi-
mate cause of a disaster.
Reasonable and clearly written codes, standards, and regulations that emerged in recent
years improve construction safety, but the best ways to mitigate failures obviously are com-
petent designs, good construction practices, utmost care, strict inspection, and unwavering
enforcement of high standards.

WHAT ARE TEMPORARY STRUCTURES?

Young engineer: Sir, what is a temporary structure in construction?
Old contractor: Whatever it takes, sonny.
Indeed, although there is a long list of temporary structures identified by name or func-
tion, anything that is erected and used to aid in the construction of a permanent project
should fall under the designation of temporary structure in construction.
As defined in the McGraw-Hill Encyclopedia of Science and Technology:

Temporary structures are those structures that are erected and used to aid in the construction of a
permanent project. They are used to facilitate the construction of buildings, bridges, tunnels, and
other above and below-ground facilities by providing access, support, and protection for the
facility under construction, as well as to assure the safety of the workers and the public.
Temporary structures are either dismantled and removed when the permanent works become self-
supporting or completed, or they are incorporated into the finished work. In addition to new con-
struction, some temporary structures are also used in inspection, repair and maintenance work.
The long list of temporary structures includes: cofferdams; earth-retaining structures; tun-
neling supports; underpinning; diaphragm/slurry walls; roadway decking; construction ramps,
runways and platforms; scaffolding; shoring; falsework; concrete formwork; bracing and
guying; site protection structures such as sidewalk bridges, fall protection boards and nets,
barricades and fences, and signs; and all sorts of unique structures that are specially conceived,
designed, and erected to aid in a construction operation.
These temporary works have a primary influence on the quality, safety, speed and prof-
itability of all construction projects.
Many aspects of temporary structures (such as design philosophy, loads, allowable stresses,
materials, methods, workmanship, tolerances, field inspection and control, use and abuse) are
different from those of permanent structures. The reference literature on temporary structures
is scant. [At the time of this writing the Handbook of Temporary Structures in Construction,
2d ed., is the only comprehensive book on the subject in the United States.] Codes and stan-
dards do not provide the same scrutiny as they do for permanent structures. Typical design and
construction techniques and some industry practices are well established, but responsibilities
and liabilities remain complex and present many contractual and legal pitfalls.

For an extensive treatment of the subject of temporary structures with detailed descrip-
tions, illustrations, and discussions of their design, construction, maintenance, and removal,
see Handbook of Temporary Structures in Construction. 2