Page 40 - Modern Steel Construction (April 2019)

Blueprint22 Photography

Two Chicago Transit Authority projects, both on the elevated train
system’s Green Line, use curved steel to create two very different
structures—one a steel and glass shelter over a station platform and
the other a “muffler” over a university building.

Naotake Murayama

Blueprint22 Photography Jeremy Atherton
of adjacent arcs form an angle and are completely distinguishable is due to the necessary bending moment needed to induce the
from one another, then the two arcs or radii in question are not second curve, which is required due to machine limitations. Most
tangent and, as described above, would either need to be pressed/ members can be redesigned to achieve this mid-tangent. In some
kinked at that point in order to achieve the desired geometry or be cases, and with special machinery, it is possible to eliminate or
miter cut and have a connection placed between the adjacent arcs. drastically reduce the straight needed in between opposing curves.
Designing with tangential arcs or radii simplifies the curving pro-
cess and is necessary to achieve the desired geometry when using What is the maximum geometric camber that I can specify
bending-rolling methods without pressing or kinking. for, say, a W27 rolled beam?
The capabilities of bender-rollers and fabricators vary, as do the
Is it possible to put a 90° bend in a pipe? equipment used and the cost. A tighter radius can often be obtained
Yes. The key factors are the radius and the bending method used. using a more sophisticated and costly process. It is best to speak
You will need to contact a bender-roller or a fabricator to discuss with a bender-roller and a fabricator to get their opinions.
the limits, options and costs.
Is there a minimum radius for bending?
When are reverse curves necessary? Minimum radius is merely a concept. Each bender-roller has their
It is sometimes necessary to design reverse curves with a small own practices, machinery and developed technologies that, when
amount of straight or tangent in between opposing radii. This applied to specific rolling jobs, can produce very different results.

40 | APRIL 2019