Page 42 - Modern Steel Construction (April 2019)

including 5%” as in-house tolerances)
but seeing that there is not an established
AISC tolerance on the amount of accept-
able cross-sectional distortion of a curved
member, it is always best for architects to
design with this in mind.

Bending Geometries
There are various geometries
available for curved members and
the methods used to bend them. Due
to the wide variety of bending equip-
ment available, almost any structural
shape can be curved, including HSS,
hot-rolled open sections, welded
built-up members and multi-sided
shapes formed by cold bending.
Standard bends are the simplest
type, where a member is bent about a
principal or geometric axis to form a
single-radius curve. Members can also
be bent about a non-principal axis or
about more than one axis, providing
three-dimensional curvature. Bender-
roller companies have the capability to
provide multiple arcs within a member,
as well as parabolic, elliptical and other
non-circular bends. Spirals are another
common specialty bend.
Because each bender-roller has dif-
ferent capabilities, early communica-
tion of bending requirements will allow
potential complications to be addressed
in the preliminary design stages. The
following are different bending types, as
detailed in Design Guide 33.
Standard bends. Standard bends
are those where a member is bent about
a principal or geometric axis to form a
single-radius curve.
In this case, the member can be bent
about the weak axis, known as bending
the easy way, or bent about the strong
axis, known as bending the hard way.
Hard-way and easy-way bending are
sometimes called camber and sweep,
respectively. However, be aware that above: Bending orientations for various types of steel members.
Fig. 2-2. Bending orientations.
these terms are typically also used to below: Curving round HSS. An off-axis bent wide-flange member.
describe mill tolerances or a small cur- AISC DESIGN GUIDE 33 / CURVED MEMBER DESIGN / 11
vature induced in a beam to partially
offset gravity-load deflections. Standard
bending orientations for several com-
mon structural shapes are illustrated in
the chart at right.
Off-axis bends. For off-axis bends,
also called conical rolling, the member
is curved about a non-principal or non-
geometric axis. Most off-axis bends are
fabricated with a constant rotation rela-
tive to the plane of curvature; however,
they can also be formed with a variable

42 | APRIL 2019 (a) I-shape
Fig. 2-3. Off-axis bends (courtesy of AISC Bender/Roller Committee).