Structural collapse during steel erection continues to be one of the “Deadly Dozen” hazards, and the failure to stabilize cantilevered structural members is one of them. When buildings or structures are designed with cantilevered members, preplanning is necessary to determine what temporary support or erection aids are needed to prevent structural collapse during the erection process.
When the field connections are designed with bolted holes and/or welded connections, it may be necessary to temporarily support the structural members until the entire connection has been completed. Erection aids are commonly specified for cantilevered connections, but in some cases such specifications may not be denoted. Shop and erection drawings should show all erection aids and necessary instructions for the steel erection contractor. Erection aid preferences may vary from area to area and from company to company.
The drawing above is a typical cantilevered member that is shop fabricated with lugs for using turnbuckles to support and position the cantilevered beam until the connection is completed. Other methods to provide temporary support may include the combination of wire rope slings and come-a-longs, or use of vertical shoring beneath the cantilevered members.
Because the steel erector is the party who actually erects the steel, they are responsible for determining the type and strength of the aids. The American Institute of Steel Construction (AISC) Code of Standard Practice provides guidance regarding this type of responsibility. This can be discussed at the preconstruction meeting between the steel erector and the fabricator. Afterwards they can coordinate with the engineer of record and the architect. The decisions pertaining to erection aids for cantilevered members must be made prior to proceeding with detailing.
Following is the standard from the AISC Code of standard Practice pertaining to the erection and stability of cantilevered members.
AISC Standards – 16.3 – 42 Section 7.10.3 – The erector is responsible for installation of all members (including cantilevered members) to the specified plumbness, elevation, and alignment within the erection tolerances specified in this code. The erector must provide all temporary supports and devices to maintain elevation or position within these tolerances. These works are part of the means and methods of the erector and the owner’s designated representative for design need not specify these methods or related equipment.
The Occupational Safety and Health Administration (OSHA) is a regulatory agency that sets forth a specific standard pertaining to cantilevered members and maintaining stability during the erection process.
OSHA Subpart R – Steel Erection 1926.756(a)(2) - A competent person shall determine if more than two bolts are necessary to ensure the stability of cantilevered members; if additional bolts are needed, they shall be installed.