Monthly Archives: July 2011

Angle Bending: Angle Iron Behaves Badly When It Is Curved

As anyone who has tried to bend a structural angle has experienced, it is difficult to roll the member perfectly square.  Angle bending causes the metal section to twist because the easiest way for it to bend (the weakest section modulus and moment of inertia) is either apex-out or apex-in and not leg-out or leg-in.

Consider what is happening when we try to bend an angle leg-out.  The vertical leg of the angle is being rolled the “easy way;” the horizontal leg the “hard way.”  But because the two legs are connected, the center of mass / neutral-axis is somewhere between the two legs.  Any material inside the neutral-axis undergoes compression.  Any material outside the neutral-axis sees tension or stretching.  The stretching is limited to about 25% elongation or strain.  The compression limit is trickier to define because it will buckle / ripple long before the ultimate compressive strain of the material.

Leg-in angles are the hardest to roll, partly because the thin innermost edge is under the most compression (because it is farthest away from the neutral axis). Often we see an offset in the vertical leg. 

With the proper machinery, tooling and operator, however, we can avoid all this bad behavior and end up with perfectly square rings.

Rolled angle rings are often used as flanges to connect cylinders or pipe and can be supplied with or without bolt holes in either or both legs.

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How Can You Minimize Freight Costs When Shipping Curved Steel?

Curved steel is found in architecture, OEM component parts, fittings for mechanical contractors, and even in art.  Part of the overall price of the product is the shipping cost.
There are several tactics to minimize the freight expenses involved:

• Combine shipments of curved steel going to a given region;
• Ship by rail;


• Work with a company close to the supplying steel mill so that the combined mileage from mill to bender/roller to fabricator is lessened;
• Work with a bender/roller whose trucking firms offer deep discounts;
• Maximize the tonnage of curved steel shipped on a truck by loading it effectively, for example, tilting a plate on a truck to avoid over-width charges or cutting curved sections to fit better;

• Coordinate inbound and outbound shipping so trucking firms are not “dead heading,” i.e. traveling without freight.  Alternately, when customers ship in loads of steel, the inbound trucks can then carry curved steel to the customer after they have dropped off the raw material.
• If the rolling firm can perform quickly, it is possible to curve the steel while the carrier waits to minimize traveling distance and time.

Work with bender/rollers to maximize the value of curved steel by minimizing freight costs. 

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Large-Corner-Radius Forming and Curving Steel

Steel plate or steel sheets are used in angle bending and bending channels.  Only very large quantities (5000 feet) can be economically roll-formed.  So most parts are formed on a press brake with a vee-die setup.  The inside corner radius is typically 1 to 1.5 times the thickness of the material.  This would be the “standard” inside bend radius. 

However, many designers are specifying large radius corners in their parts for both aesthetics (a smoother rounded corner) and function (avoiding sharp corners).  Forming these larger radii requires different tooling sets for each bend radius.  Roll curving these large-corner-radius formed parts can be difficult– especially keeping the corner radius intact. 

This stainless formed angle is formed with a 2 inch bend radius, and then rolled to a 12 inch radius which is used as a curb bumper for toll booths.

This ¼” shroud is formed to an obtuse angle with a 2” radius and roll curved to a large parabolic curve to match the curvature of a bridge.  It will cover the lighting that runs along the arch of the bridge.

This 12ga stainless channel is formed to a 1.5” radius and then rolled to a 30” radius.

It will be used in metal ductwork as a stainless steel elbow in food processing plant.  The large radii prevent materials from building up in the corners.

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When There Are No Pictures to Communicate Specifications for Bending Steel Sections, Use Everyday References

Of course a picture is worth a thousand words, but what happens when you don’t have a picture? Customers call from the field to describe how they want their steel curved.  We love everyday references to help us describe the section bending:

Everyday References:

–The “belt around your waist” (easyway flat bar) versus the “flat washer” (hardway flat bar).

 “Like an old-timey straw hat without the top” (angle leg out where the brim would be the leg out).

In describing the degrees of arc, many people use the clock as a reference. One guy called and said the hand on his clock (radius) was 84 inches, and he needed enough arc to go from 12:00 to 9:00.

“Ok, great.  You need 270 degrees of arc (almost a full turn).”
“No, I only need 90 degrees,” he replied.  We had a good laugh about which way his clock runs.

Many customers split our rolled pipes in half to make half-pipes, which can be split “pocket in,” “pocket out,” or “like a bagel.”

The threads on a screw describe a right hand helix.

Got any more everyday references to describe steel bending?

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Curved Steel Makes Pedestrian Bridges Less Pedestrian.

I.e. less ordinary and more exciting. Pedestrian bridges incorporating curved steel often combine aesthetic appeal with functionality beyond providing a route to get from here to there.

When it comes to aesthetics, the design of crisscrossing pipe for Tempe Town Lake pedestrian bridge is open, elegant and clean.

As for functionality, the bridge, which is currently under construction, connects the northern and southern shores of the lake so that thousands of bicyclists, runners and walkers won’t have to deal with cars. 

But the bridge will serve an additional infrastructure purpose:  it will shade rubber bladders which form a dam.  Furthermore, the bridge will have a sprinkler system that will also keep these bladders cool and wet to prevent the kind of deterioration that had caused a flood recently.

The snake-like pedestrian bridge designed by internationally renowned architect, Frank Gehry, complements the curves of his music pavilion, allows for the passage of pedestrians from the concert area of Millennium Park towards Chicago’s Lake Michigan, and additionally serves as a noise barrier between busy Columbus drive and the music venue.

Also in Millennium Park is the Nichols Bridgeway designed by another famous architect, Renzo Piano.  In deliberate contrast to Gehry’s sinuous design, Piano’s bridge looks like a sleek racing yacht with a curved hull and a flat deck.  Offering a passage over Monroe Street, the structure provides wonderful views of the park, the lake and a variety of significant architecture including buildings on Michigan Avenue and Piano’s new Modern Wing of the Art Institute of Chicago.  But perhaps the most important feature of this bridge is that it drives traffic from Millennium Park to the Museum.


Curved steel can help make pedestrian bridges less pedestrian by increasing their beauty, by enhancing the experience of crossing the bridge, and by serving additional purposes like protecting the infrastructure,  muffling noise at a concert, and driving visitors to a museum.

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Bending Steel Sections: How Long Does It Take?

How much lead time is for required for bending steel sections?  How long does it take to fabricate curved steel?  What is the schedule impact?  Architects, engineers, and structural steel fabricators regularly ask these questions of Benders and Rollers, companies that specialize in curving steel.

The answers vary, of course, from company to company depending on its capacity, its processes and its overall responsiveness.  Many Bender/Rollers can easily fulfill an order to curve a few beams, for example, within a two-week time span.  Larger orders might take longer, but often the customer, typically a structural steel fabricator, will be happy with an initial partial shipment so he can begin his fabrication.  The Bender/Rollers most often simply curve the steel so their turn-around time is usually faster than a fabricator’s because the latter has more work to do on the steel sections.

The trend over recent years seems to be that the Bender/Rollers are offering faster and faster turn-around times.  At Chicago Metal Rolled Products, for example, we have offered three-day, two-day, one-day and same-day service.  Truckers will haul in beams as large as W44 x 290, drop them off, go to McDonald’s for lunch during the beam bending, come back, and load up the curved steel sections destined for the fabricator’s shop.

Quick turn-around times are sometimes required because although the project’s due date remains firm, delays in permitting, engineering approval, design revisions, etc. can impact the schedule.  In most instances, however, curved steel can be supplied quickly enough for any project’s schedule.

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Beam Bending: What Is the Longest Beam That Can Be Curved?

Perhaps this beam bending question asked by architects, engineers and fabricators is best divided into two parts:  What are the longest beams that are produced.  And, given those lengths, is there a length limit as to whether they can be curved.

Nucor-Yamato Steel’s cooling bed on NYS-1 mill is about 240′ long, but the steel sections would be cut into shorter/stock lengths. The NYS-2 mill cooling bed is about 125′ long (for their larger/deeper sections). Therefore, the longest large sections that they make available would be about 125′ long, but most are much less.

The length limitation of Steel Dynamics (SDI) is governed by which of their 2 mills (heavy Section (HSM) / medium Section (MSM) produces the beam.  Off the HSM, SDI can and does roll and ship by rail or truck up to 125’ (assuming routing can allow).  The offset for additional length is generally shipping costs: reduced capacity on rail cars to allow overhand swing (therefore more $/ton), extra $$ for idler cars, etc., and by truck: cost of permits and escorts.  Off the MSM SDI is currently limited to 75’.

So, given that heavy beams can be produced to 125 ft. long, can they be curved?  Generally beams this long would not be rolled to a tight radius unless the length was chosen to provide a good yield of  shorter curved segments.  If the beam were to be shipped in one piece, too tight a radius would create shipping width limitations.

Another limitation, of course, arises from the capacity of the bender/roller, the company to provide the structural beam bending.  A bender/roller would have to have the crane capacity and under-hook height to lift steel sections weighing 40 tons or more, would have to have the heavy machinery to perform the beam bending, and would have to have the floor space of more than 125ft on either side of the section bender. 

Another restriction arises from shipping the long curved beams.  The length and width of the curved beams would be limited by the capacity of a particular truck.  Then there are state restrictions. A common “legal” load without permits is 102in wide x 52ft long.  With permits (which vary from state to state) a loa–under several restrictions–can be as wide as 16ft, as long as 145ft, and as heavy as 120,000lbs (trailer and load).  Length is not usually an issue.  The defintive answers can be obtained through those companies who specialize in oversize loads.  They can tell you the limits of their equipment and the limits of  each state’s permits. 

So . . .  very long and very heavy beams can be produced, curved and shipped.  The architects, engineers and fabricators who have inquired about what can be done can use this information as they seek the optimal designs for their projects.

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Steel Plate Rolling: Forming and Shipping Long Plate

Rolling plates, that are 30 to 45ft long, will produce challenges not only for the steel plate rolling itself but also for shipping the material. Depending on the diameter and the thickness of the material, as the plate passes through the forming rollers it will – if not supported properly—under the force of gravity just “relax” back to a straight flat plate. Using the jargon of the shop floor, during the plate rolling, the plate was “broken” but did not hold its “set.” Typically, if the plate did not have gravity working against it, it would more easily conform to the desired radius. A solution to this plate rolling problem is to use some device to support the plate, either from above by a crane, or from below by an auxiliary roller. Some plate rolls have support rollers built into the frame for this purpose. Other plate rolls have a vertical orientation to combat the effects of gravity.

Once the plates are rolled, however, there is also the issue of how to ship them without their losing their radius. A built up support in the middle of a 40 or 45ft flatbed can be used to ensure the plate does not lose its form. The plate would be placed on the trailer convex to the sky.

Alternately, two built up supports can be secured at the ends of the flat bed. In this case the plate would be placed on the trailer concave to the sky. We at Chicago Metal Rolled Products call the first method “frowny face” and the second “smiley face.”

Needless the say, the most critical factor in handling, forming and shipping long plate is safety. It is incumbent upon all involved that all equipment is in proper working order—plate rolls, cranes, chains, clamps, supports, flatbeds, etc.–and that all operators are following proper safety procedures. Done right, rolling and shipping long plate can reduce the number of welds in a project, can provide a more aesthetically pleasing product, and can otherwise save time and money in most applications.

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