Page 316 - Forensic Structural Engineering Handbook

TEMPORARY STRUCTURES IN CONSTRUCTION 10.5

• Condition of the member and its material (new, used, damaged, deformed)
• Acceptable behavior of the structure (such as tolerable deflections, and vibrations)
• Allowable degree of unacceptable behavior
• Acceptable probability of total failure
• Consequences of failure
• Construction tolerances
• Workmanship in the construction
• Inspection standards
• Protection of the structure against damage, deterioration, and extremities of weather
• Intended life-span of the structure with increasing probability of occurrence of maximum
loads, abnormal loads, damage, and deterioration with time

Probably not all these factors were explicitly weighed in the establishment of a particular
design load or allowable stress in a code, standard or specification, but they were inherent
in the evolution of the values used by the engineering profession today.
A discussion of these factors is beyond the scope of this chapter. The reader is urged to
make a column alongside the above list and note what the equalities and the differences are
between permanent structures (such as a building) and temporary structures (such as false-
work and shoring). The differences will outnumber the equalities.
Clearly, at least some of the design criteria should be, and indeed are, different for tempo-
rary and permanent structures. (For that matter, at least some of the design criteria for a struc-
ture during its construction phases should be different from the criteria used for its completed
form.) The numbers—the values of the design loads—may work out to be the same even if the
criteria for their development are different. But we do not know that until we do it.
The most complete and up-to-date public document outlining a design philosophy and
specifying design loads and load combinations for temporary works is believed to be the
3
SEI/ASCE 37-02, Design Loads on Structures During Construction Standard, developed
over periods of many years, and first published by the SEI/ASCE Design Loads on Structures
During Construction Standards Committee, chaired by the author, in 2002. (At the time of this
writing the standard is being updated and revised by the committee for republication in 2010.)

Drawings. Who performs the design of a temporary structure, who makes the drawings,
and how much detail is required in the specifications vary depending on the particular
temporary structure under consideration. In an extremely complex job involving such
temporary work as a coffer dam for a bridge pier, or a method of driving shafts for a tun-
nel, the design of the temporary structures will often be done, and the drawings prepared
by the designer of the permanent project. It will then be the responsibility of each con-
tractor to build the temporary work in strict accordance with those drawings. On the other
hand, for simpler types of temporary structures, such as a temporary ramp that might be
used by an excavation contractor for a building, the excavation contractor will likely do
the designing.
Between the extremes are the types of temporary structures for which specialty contractors,
who make a business of doing specific types of temporary structures, will be employed to pre-
pare the designs. Examples of this include concrete forms using patented panels. The drawings
by the specialty contractor will look more like shop drawings with lots of specific details.
It is well established that the contractor who builds in accordance with the design that
is provided by another party, is not responsible for the adequacy of the design or for bringing
about the result for which the design was intended, provided that in his work the contractor
strictly follows the design. However, the contractor who does provide the design himself, is
responsible for both the adequacy of the design and its fitness for the intended use.