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 dont 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.
Theres no doubt the recently released Design Loads on Structures During Construction fills a critical need. Ironically, however, and contrary to the statement in ENRs editorial, it is unlikely that the standards 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, well have a place to put it.
Taking the First Step
November 11, 2002