Page 39 - Modern Steel Construction (April 2019)

Freyja Bardell
of the material. Also, keep in mind that varying amounts
of extra material are required at one or both ends of the
member, depending on the process used; you don’t want
to have to splice additional material to one or both ends.
Talk to a bender-roller about the best options for your
particular application as well as their capabilities. The
various bending types and methods are discussed later in
this article.

Does AISC impose any tolerances on curved beams?
There are limited tolerances for curved members in the
AISC Code of Standard Practice for Steel Buildings and Bridges
(ANSI/AISC 303, a free download at www.aisc.org/
specifications.) According to Section 6.4.2, “For curved
structural members, the variation from the theoretical
curvature shall be equal to or less than the variation in
sweep that is specified for an equivalent straight member
of the same length in ASTM A6/A6M.” Other acceptable
tolerances, such as any cross-sectional distortion, are
not generally available because they are dependent on Freyja Bardell
whether the member is AESS as well as any effect they
may have on the member strength. AESS tolerances are
discussed in Section 10 of the Code. The actual geometric
imperfections for rolled members are dependent on
several factors, including:
• Cross-sectional shape of the beam
• Bending radius
• Bending axis
• Bending method used by the bender-roller
• Equipment limitations of the bender-roller
It is best to discuss the required tolerances with the
bender-roller who will provide the service—and be sure to
add the required tolerances to the contract documents to
ensure that you get what you are asking for.
What are some considerations for members with
multiple curves?
Designing compound/multi-radial members allows
architects to bring a “wow” factor into their design, but above: The “Lupe” sculpture, which lives at the Lower Guadalupe Trail in San
Jose, Calif., is comprised of 78 layers of bent steel pipe, stacked and welded to
it also helps in eliminating connections (especially if the form a full-scale mammoth.
shrinkage/growth of curved members and the specified
connections of those members is a consideration). It is below: The new curved canopy at Hartsfield-Jackson Atlanta International Airport.
important to understand and grasp the idea and principle
of tangential arcs. When a design calls for a single member
with adjacent arcs of differing radii—commonly referred
to as a compound or multi-radial member—it is extremely
important to design the arcs tangent to one another. If the
arcs are not designed tangential to one another, then it is
like having a miter cut at that point, or having to bend the
member at that point with a press brake or a three-point
gag press/ram bending machine.
The question arises: How do you know when arcs are
tangential to one another? The answer can be found in the
detailing or dimensioning of the arcs. When arc dimen-
sions are pulled on each of the radiused portions of the
curved member, one can tell if the arcs are tangential by
looking at the leader lines of the arc dimensions. If adja-
cent dimensions’ leader lines fall exactly over one another
and cannot be distinguished from one arc to the next, then
the adjacent arcs/lines are tangent. If the two leader lines

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