The American Institute for Steel Construction (AISC) specifies the standards for steel construction in its Code of Standard Practice for Steel Buildings and Bridges (COSP). The COSP defines the “the trade practices that shall govern the fabrication and erection of the Structural Steel” . . . “in the absence of specific instructions to the contrary in the Contract Documents.” The standards, therefore, are the default trade practices.
A group of subcontractors, sometimes called “Bender/Rollers” or “Rolling Houses,” specialize in structural steel bending for structural steel fabricators. The COSP tolerances for curved structural steel sections, however, do not apply to the Bender/Rollers but rather to the fabricators whose projects incorporate this steel. Furthermore, the standards apply to the curved sections after they have been fully fabricated, e.g. cut to length, welded with base plates, or reinforced with gussets.
Needless to say, however, the tolerances actually held by the Bender/Roller for a given project often affect the ability for fabricators to achieve the tolerances specified by the COSP or by alternate and explicit instructions in the Contract Documents. If the Bender/Roller is supplying, for example, W36x230# beams curved the “hard way” (x-x axis) to a 170 ft. radius, the fabricator will have difficulty improving on the tolerances held by the Roller/Bender. The application of heat and/or force in a fabricator’s shop may not move a section from being out of tolerance to being in tolerance. Alternately, a flimsy 1 x 1 x 1/8 angle curved to that radius could probably be pushed into tolerance by hand and will not present problems for the fabricator. Generally speaking, the more closely a Bender/Roller can curve a section to the specified radius, the easier it will be for the fabricator to fabricate to the specified radius.
In conclusion, the fabricator and the Bender/Roller should communicate expectations regarding tolerances to assure that a given project incorporating curved steel moves forward smoothly and with high quality.