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Taking the First Step
From my perspective
as a practicing structural engineer active in code writing
bodies, a member of the American Society of Civil Engineers’
7 Load Standard and chairman of the Task Committee on Wind
Loads, I offer some comments on the proposed new load standard
described in "Tool May Reduce Jobsite Fatalities"
(ENR 10/7 p. 10). First, the standard is a good first step
in requiring our industry to address the load effect on a
building under construction. This topic has been largely ignored
until now.
For those of us
active in design of long-span roofs where the largest loads
are very likely to be realized during the erection process,
we are acutely aware of this issue and that the "means
and methods" of construction are intimately tied to the
structural design. In essence, we undertake many of the requirements
for this structure type that are contained in the new standard.
And we state erection requirements in the project specifications
for the contractor to follow. If the contractor wishes to
modify the proposed erection procedure, a qualified engineer
must oversee the changes.
I have been concerned
with the strict boundary line placed between structural design
and the means and methods of construction in this country.
This practice has not served us well when it applies to the
safety of the structure. I have observed that Gustave Eiffel
did not make any such distinction when he financed, designed
and built his great bridge structures and the Eiffel Tower.
We can learn from the past on this issue.
Within ASCE 7,
we are undertaking a review of the wind requirements of the
new standard. I am sure changes will be recommended in this
area and other areas of the document. I envision this as a
document largely ignored at first but eventually evolving
to be routinely cited in the design/construction world. However,
it will take time for sure.
The need for this
document is real. We should recognize that structures don’t
make a distinction of where the external loads come from or
their timing in the process. All engineers and builders should
pause and reflect on the fact that a structural overload and
failure can happen anytime in the life of the structure, starting
from the day the first member is lifted into place. Design
of the structure in its final form is well addressed in our
codes and design process. The time spent evaluating what goes
on during construction is far less, and it can be a case of
"cross your fingers and hope for the best." The
new document will at least get the ball rolling.
There’s
no doubt the recently released Design Loads on Structures
During Construction fills a critical need. Ironically, however,
and contrary to the statement in ENR’s editorial, it
is unlikely that the standard’s adoption would have prevented
the 1998 Four Times Square hoist collapse (ENR 10/14 p. 64).
Why? Because this edition of the standard does not directly
address the loadings to be used for design of "runback"
structures. (A runback structure is a scaffold-like structure
that braces the hoist to the building and provides platforms
for accessing hoist cars from the building.
Having reviewed
the structural design of a number of these structures, it
is apparent there is currently no consensus on design loads
for components supporting multiple levels. But at least once
that information is developed, we’ll have a place to
put it.
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