Creating Curves:
8 things to know about curved metal panels
Marcy Marro, Managing Editor,
Posted
10/01/2012
While the majority of your projects
may require basic straight metal wall and roof panels, some will
require panels to be curved. Whether the project calls for curved
roof or wall panels, there's a lot to know about curving metal
panels. Metal Construction News talked to some
industry experts to learn more about what is required when a
project calls for curved metal panels.
1.) Types of Curved Panels
Curved panels can come in a variety of shapes. Barrel-vaulted,
or convex curves, are the most common version where the roof design
consists of an outward consistent curvature that creates a convex
shape. A reverse curved roof, with the curve turned inward, is
known as a concave curve.
Some manufacturers also offer a complex curvature, known as an
S-shaped curve, which combines a concave and convex curve. In
addition to single- and S-shaped curves, Curveline Inc., a metal
panel curving service based in Adelanto, Calif., also forms double-
and triple-radius curves.
Michigan City, Ind.-based Kalzip Inc. offers elliptically and
hyperbolically curved panels, in addition to convex and concave
panels. Called XT Profiles, the freeform elliptical and hyperbolic
curves are applied to Kalzip's standing seam sheets for use with
complex curved roofs, allowing architects' unrestricted design and
flair when it comes to curved surfaces, as Paul Stringer, technical
support engineer at Kalzip's U.K. location, explains.
2.) Curving Methods
There are a variety of methods through which a panel can be
curved. Stringer describes the basic curve as a natural curve that
the panel will naturally curve to, without being forced or
excessively strained, which would create visual deformations and
possible creases. This can also be known as the "lay-down" or
"walk-down" method, as George Jones, director of field services at
IMETCO, Norcross, Ga., calls it. "For large radii, the panel's
weight will cause it to naturally drop down or conform to the
substrate surfaces within reason," Jones says. "For smaller,
tighter radii, the same approach is utilized, but the installer
will be forcing the panels down and holding them in place with the
panel clips."
A mechanically curved panel creates a curve that is tighter than
what its natural curve will permit. Panels start as a straight
profile and are curved by a machine that physically alters the
panel by a set of forming and curving rollers. Jones explains that
the rollers stretch or compress the straight panel into a curved
shape. "These curving rollers can be mounted to a standard panel
roll former, or can be a separate operation," he notes. "Both of
these methods provide a consistently curved panel that will follow
a consistent curved substrate."
A third method is called crimp curving. "Crimp curving is
typically used where there is a continuation of the roof down the
building façade and a soft visual edge is preferred to a sharp
edge," Stringer says. "The crimping is as the word implies, has an
undulating surface that is introduced by pressing the sheet with
indentations to achieve the required radius. The crimping process
allows for reasonably tight curves to be achieved, though at the
expense of a localized corrugated surface to the radiused area."
Crimp curving is the process that Curveline uses to curve its
panels, and according to Dennis Klocek, AIA, CSI, product manager
at Curveline, this process actually increases the structural
integrity of the panel.
3.) Material Selection
While just about any material-stainless steel, galvanized or
Galvalume steel, copper, zinc or aluminum-can all be used for
curved metal panels, some materials are easier to bend than others.
"Aluminum tends to allow for a tighter curve with many panel
systems," says James Bush, vice president of sales, ATAS
International Inc., Allentown, Pa. "It may also allow for
flexibility for field adjustment, as often a true curve is hard to
build with various substrates to which the panels are applied."
"For curving metal panels, the softer more ductile materials are
often preferred, but not required," adds Jones. "For larger radius
conditions, any material can be utilized, but for tighter
conditions, copper, zinc and aluminum are preferred. The most
cost-effective approach is to use steel for larger curvature while
using aluminum for the tighter applications."
4.) Panel Thickness
When it comes to how thick of a panel to use for a curved
application, thinner materials are easier to curve because there is
simply less material that is needed to conform to the desired
shape, explains Kurt Schievelbein, technical manager of rollforming
operations at Berridge Manufacturing Co., San Antonio.
Bush explains that for aluminum, the common substrates are 0.032
and 0.040, and for steel, 24- and 22-gauge panels. These are the
same for architectural straight panels, as well, Bush notes. For a
tighter curvature, Jones recommends 24-gauge steel, which Berridge
also prefers to work with.
Jones also notes that 0.040-aluminum, which has more mass, might
allow some manufacturers to mechanically curve the panel to a
tighter radius. "With more mass, the 0.040-aluminum can better
withstand the stretching or compression that occurs when
mechanically forming the panels," he says.
5.) Panel Length
The length of a panel that can be curved may vary by
manufacturer and where the panels are being curved. There will be
more limitations for panels curved in a factory versus those curved
on the job site. Also, shipping coils to a job site for curving
will allow for longer panels than if panels are shipped
pre-formed.
While Curveline can curve a panel up to 34 1/2 feet long in a
factory, Michael Gorski, machine department manager at Englert
Inc., Perth Amboy, N.J., says that they've seen panels curved up to
100 feet on the ground at a job site. But, if the panels are curved
on the roof, the available space will determine the panel
length.
"The longer the panel, the more easily the radius can be
compromised if the panel is not allowed to conform to its natural
shape as it exits the rollformer," Schievelbein says. This means
that when 3 feet of the panel have exited the machine, it will take
much more force to bend or flex the panel than if 30 feet had
exited the machine. "The panel acts as a lever arm, allowing longer
panels to be more easily bent than shorter panels," he adds.
6.) Radius of Curved Panels
The minimum radius of the different types of panels needs to be
kept in mind when designing curved applications. Schievelbein
explains that some of Berridge's panels can be curved to a minimum
radius of 20 feet, while others can be curved to a minimum of 4 or
8 feet.
If a panel does not fit the desired radius very well, forcing it
to conform risks buckling and/or waves in the vertical legs or
panel pan. "It can also place a lot of stress on the fasteners and
clips being used with the system, making the system more likely to
come apart and fail over time," he adds.
Additionally, Schievelbein says mechanically seamed panels are
typically able to handle higher uplift loads and wind speeds than
other panel systems. They can also be more difficult to curve to
smaller radii. "When designing for coastal or other high wind speed
areas, it's best to determine the wind uplift requirements for that
area to determine what type of panel is needed," he explains. "Then
determine the minimum radius the panel can handle and proceed with
the design accordingly."
7.) Factory-Forming vs. On-site
Forming Panels
While panels can be formed either in a factory or on the
construction site, not all companies provide on-site curving
options. Some, such as Curveline, only factory-form their curved
metal panels.
Panel length is one of the biggest concerns for factory-formed
panels since panels needs to fit onto a standard tractor-trailer
for shipment. "In the event the curvature is beyond what can be
transported, field curving of the panels would be required," Bush
notes.
When forming curved panels in a factory, it is important to have
enough space for the panel as it exits the machine. "Longer panels
formed to a smaller radius will require more space to the side of
the machine when existing than shorter panels formed to the same
radius, or panels of a similar length formed to a larger radius,"
Schievelbein says. Since it can be deceiving trying to guess where
a panel will go as it exits the rollformer, he recommends allowing
more space than expected.
Getting the correct radius can also be an issue with curving
panels in a factory. "Contractors must provide accurate radius
dimensions," Jones says. "No last-minute field adjustments are
possible."
(For more on curving panels on-site, see sidebar.)
8.) Panel Appearance
"As the appearance of metal panels often reflects the true
flatness of the metal deck, one must be aware that the curved
substrate should be smooth and consistent," Bush advises. "Care
must be taken to ensure the as-built dimensions coincide with the
actual construction drawings so that the fabricated panels fit the
construction."
Jones notes that often times, the lay-down or walk-down method
of curving will create an unsightly visual effect ranging from an
oil-canned appearance to very visible crimps/creases at the
fastener or clip locations. "Tighter substrates require a greater
degree of force, which will result in an even more obvious
unsightly panel appearance," he adds.
 Curving Metal Panels On-Site
When curving metal panels on the job site, there are many things
to keep in consideration.
While there are no restrictions on panel lengths or the degree
of radius, George Jones, director of field services at IMETCO,
Norcross, Ga., notes that field-forming panels risks leaving them
exposed to weather and job-site conditions. It is important that
the panels and/or coil are protected from weather conditions, such
as cold temperatures, rain, snow and wind. Wind-blown debris can
also interfere with equipment and personnel, delaying field
operations.
It is also important to make sure that there is adequate curving
and staging space at the job site. In some cases, the site must be
prepared and graded level to receive the equipment, Jones adds. Any
delays can result in increased costs for the project.
Running shorter test panels to check the roof's actual radius is
one of the most important things a contractor can do,
says Michael Gorski, machine department
manager at Englert Inc., Perth Amboy, N.J. "If the radius is too
much, or too little, this will cause oil-canning of the panels when
they are put down on the roof."
Kurt Schievelbein, technical manager of rollforming operations
at San Antonio-based Berridge Manufacturing Co., agrees, saying
that structures are not always built exactly to the design
drawings, and if the panels are curved to an incorrect radius, that
may not be usable.
"With on-site curving, live measurements and dimensions can be
taken, rather than the design drawing dimensions to provide
accurately produced curves," explains Paul Stringer, technical
support engineer at Kalzip's U.K. location.
Gorski says contractors need a special seamer to seam the panels
together, and as the panels get longer, the more manpower is
required to handle them. "As panels are curved in the vertical
position, [contractors] should also have enough stands for the
panels to run out on," he says. "This makes the panels more
consistent from one to the next."
One of the biggest mistakes Gorski sees is that contractors
don't seam the panels together as they go along. "They put down a
bunch of panels and then come back and seam them," he says. "This
is bad practice even on flat roofs."
Jones notes that it is important to have adequate personnel to
handle the panels, as they are more susceptible to buckling and
kinking during handling than straight panels. This is especially
true during installation. "Material handling will require more care
and attention to the listing operation," he says. "These panels
must be intermediately supported and stabilized during the rigging
and lifting operation. The curved panel shape is inherently
unstable and will tend to buckle, fold and distort to the point of
product damage without adequate support."
"The curved substrate is difficult to use the standard string
line method to check the substrates for a suitable installation,"
Jones adds. "Special care must be taken to look for high and low
spots in the substrate deck. Using adequate shim heights at the
panel clips will level the panel height and allow for proper
material thermal movement. If the panels are not allowed to expand
and contract freely, this thermal movement can result in oil
canning."
Some manufacturers will send trained personnel to the job sites
with the curving machines, while others, like Englert, offer a
training program for first-time users.
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