Category Archives: Pipe Bending

Galvanize Pipe Jackets Reinforce Communication Towers

A 167’-7” tall, Verizon Wireless communications tower, atop Smelter Mountain in Durango, Colorado required a structural upgrade on its 3 existing tower legs. The tower had originally been built with 2” to 3” standard structural pipe as its supporting legs, but after years of cyclical wind loads it was determined that the existing tower legs needed a structural upgrade. In order to reinforce the tower’s legs, engineers devised a plan to weld pipe jackets to the outer half of the existing legs, which can be seen in the diagram below.

Pipe jackets are a common term for pipe split or halved into 180 degrees. They are commonly used for heat exchangers and or coils welded to the outside of tanks. For this project the split/halved pipes are referred to as 180deg cut pipe. Various size pipes were to be split into halves, from 3” to 5” XXH and then straightened in order to surround the outer half of the existing tower legs. The additional support from the reinforcing 180deg cut pipe increases the stiffness of the tower 12x from its original design.

The pipe was split into 180deg cut pipe by way of a gantry track plasma cutting system. The pipe is fixed in order to restrict its movement when cutting and once the torch strikes an arc the movement of the cutting head is automated to eliminate any deviation from the cut line. Due to residual stresses within the pipe, from its melting and manufacturing at the mill, the pipe springs and twists open once it is fully split.  This is commonly known in the industry as the banana peel effect, and must be corrected by way of straightening. Most structural steel fabricators have the equipment to split the pipe through some sort of track cutting system, either flame or plasma, but it is the straightening of the halved pipes back to within, or better than, mill tolerance that is the challenging aspect of splitting pipe into 180deg cut pipe. For this, most fabricators seek out a bender/roller as they have the necessary equipment to bend, curve and straighten structural steel.  With the proper tooling, a machine which is normally used for bending steel can also be used for the opposite, to straighten out existing curvature.

In this case, a 3-Roll section bender with a special tooling setup was used to straighten the pipe and it was straightened to 1/8” over 10ft of length. After the 180deg cut pipes were straightened, they were bundled and sent to a galvanizer. The halved pipes were then hot dip galvanized for corrosion protection after installation. The galvanized reinforcing pipe jackets were then shipped to a terminal in Durango, Colorado where they were staged for pickup once the steeplejacks were ready for installation.

Straightened and Galvanized Steel Pipe
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Excellence in Structural Engineering Award Goes to Institute of Environmental Sustainability

Structural Engineers Association of Illinois (SEAOI) gives out an award every year to a project it feels helps encourage engineering education and advances the art and science of structural engineering. Loyola’s recently constructed Institute of Environmental Sustainability (IES) won the “Best Project” award given out by SEAOI for the Excellence in Structural Engineering Awards Competition. The judge commented that “the winter garden is an elegant curved glass enclosure with a minimized amount of structure to allow unobstructed views. The environmentally responsible IEC integrates academic and residential components of university to create space for an exciting and delightful whole student experience”.

IES – Loyola University Chicago

The crown jewel of IES is the winter garden. The winter garden is a 3,100 square foot urban agricultural greenhouse. The structure is designed using nine elliptically curved trusses that are made out of 8” SCH 80 pipe connected to 5” SCH 40 pipe though a triangular cross section configuration of a double top chord and single bottom chord system. The design of the continuously curving trusses helps minimize the amount of structure needed to hold up the glass curtain wall skin. The top roof portion of the greenhouse incorporates pipes curved to a very large 250ft radius to help maximize sunlight in the winter garden’s growing area while at the same time try to produce minimal glare to surrounding buildings. Also there is a tight 12 ft radius 90 degree bend at one end that goes down into an S shaped curve. This curvature in the steel pipe trusses design helps with passive ventilation. When you walk into the building you will notice the temperature. You are in an unconditioned environment that is not heated or cooled. The winter garden is shaped to assist natural ventilation with open end windows at both ends of the trusses. This unique curved shape of the winter garden also facilitates rain water harvesting. Water falling on the curved roof easily flows into a 3,000 gallon cistern located on the first floor. The water is then reused in the greenhouse operations for irrigation, landscaping and for flushing the toilets located off the lounge.

Curved 8″ SCH 80 and 5″ SCH 40 Pipe

In the greenhouse there will be two aquaponic systems. There are also two vertical farming installations where food crops are grown for harvest on a wall mounted lattice structure. The ecological system will grow fish and produce for food. Students taking courses in related fields will work to identify what to grow in these systems and how to process them for market. Students maintaining these gardens will sell the produce at Loyola’s famers market and through the Engrained Café. The IES is an innovative and interactive learning environment that demonstrates how students can participate actively within, as well as help to create a living/learning green community.

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Circuit of Americas Observation Tower Wins IDEAS2 Award

Innovative Design in Engineering and Architecture with Structural Steel (IDEAS2) awards are sponsored by the American Institute of Steel Construction in recognizing projects where structural steel has been utilized in an innovative manner. This year the winners were chosen from nearly 100 submissions from architectural, engineering and construction firms throughout the U.S. This year Circuit of the Americas (COTA) Observation Tower won in the category for projects less than $15 million. The COTA is a 3.4 mile motor racing circuit, the first purpose-built F1 track in the U.S. that is located just outside of Austin TX. The land mark 251 foot tall observation tower was designed by Miro Rivera Architects to give spectators unrestricted views across the racetrack’s twisting bends. The platform (which has a glass floor) provides a 360 degree panorama view of the circuit and has a capacity for 10,000 spectators.

COTA View from Above

The circuit of the Americas observation tower won the award because it combines creativity, economic and technical achievement through the use of structural steel. The observation tower is very creative in how it uses a veil like structure made out of 18 bright red closely spaced HSS 8.625” OD structural pipe that are curved running down the full height of the tower. The pipes act as a canopy for both the platform and the stage below. The design of the curved pipes was inspired by the visual imagery of sports cars and movement. The red pipes running along the tower mimic the streaks of lights trailing racecars at night time. While ostensibly an architectural feature, the veil also serves as an outrigger column for lateral load resistance via a series of struts and rods that connect it to the main tower. The tower contains approximately 385 tons of steel. The observation tower also had a technical achievement through the use of fully connected Tekla Structures program.

COTA Structural Steel Canopy

Due to the tight 10 month time frame from owner approval to race day, the complex tower structure design had to be conveyed to the fabricator so they could erect the canopy without confusion. Generally in the steel fabrication construction industry paper drawings are delivered to the steel fabricator to interpret and build, but this case they were able to bypass this step and print shop drawings directly from the model. To increase efficiency and reduce cost of bending each 8 inch steel pipe to the architects initial drawings the program helped work with a bender roller to break large radii into segments. There were a total of 70 curved 8” sch 40 pipes that start out at a tight 96” centerline radius and then get a slightly looser 360” radius before opening up to a large 1,349” radius at the bottom of the tower. The fabricator worked directly with a detailing service to electronically transfer the model into detailed fabrication shop drawings that showed the pipes in different curved sections. The construction manager, Austin Commercial, estimated that the integrated delivery process saved three months over a more conventional process. COTA is more than just a racetrack; it has become a major economic driver in Central Texas. On their website they state that from October 2013 to September 2014, COTA brought in $900 million to the Austin metropolitan area ($731 million for events and $166 million attributed to operations). During that time COTA hosted six motorsports, 18 concerts, 110 track rentals and other events that helped create 9,100 jobs through annual activities and operations.

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Curved Stainless Steel and Chicago’s Draft Town

The city of Chicago has prepared for the media spotlight this weekend as the NFL has moved its annual draft events from New York to the heart of the Midwest this year.  Tourists and locals alike can visit Grant Park to take part in a number of activities as part of the “Draft Town” built up specifically for this event.  While the draft itself is taking place at nearby Roosevelt University, the free fun takes place in the park.  Events include a flag football festival, Super Bowl museum, football celebrity autographs, and even a lightshow at the famous Buckingham Fountain, as the city changes the colors on the fountain to represent the NFL team which is currently on the clock waiting to draft.

NFL Draft Town

While visiting Grant Park, many patrons will have the chance to view some of Chicago’s finest examples of curved steel.  Always a tourist attraction, the nearby Millennium Park is an extension of Chicago’s Grant Park and contains the famous Cloud Gate sculpture and Pritzker Pavilion.  Cloud Gate, or “The Bean” as it is affectionately known, displays a 3/8″ thick curved stainless steel façade that has been polished to a mirror finish.  The complex topological curved steel surface required computer and robotic assistance to create properly.  The plates were fabricated so precisely that no on-site cutting or filing was necessary when lifting and fitting them into position to be welded together.

Cloud Gate

Nearby Pritzker Pavilion features both a curved stainless steel band shell with a ribbon like effect, as well as curved arches made from rolled pipe which varies in diameter from 12 to 20 inches.  The curved pipe trellis allows for an open lawn structure to support the speaker system and has become very popular for local music and film events.  The use of curved steel pipe was preferred by designer Frank Gehry over the alternative of using vertical columns or pipes to support the speakers as it worked together with the curved band shell more aesthetically.

Pritzker Pavilion
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Limitations of Bending Tubes and Pipes

Often, in the bending and rolling industry, we see requests which push the limitations of tube bending.  This can occur in both large and small pieces.  Sometimes a project may have been designed without considering the physical effects curving has on the material.  In these cases, design plans can occasionally be evaluated and modified with the knowledge of an experienced steel bender.

One of the most common examples in tube bending where material shape and size needs to be evaluated is tube cross-section deformation.  If you were to be rolling flat material to form a cylinder, the plate rollers are designed to sandwich the material between the rolls, completely and evenly supporting all material under the same stress levels.  Even when curving angles, rolling equipment can use dies of different shapes in order to brace the material on the interior and exterior faces, so that pressure is applied evenly.  However, when rolling a tube or pipe, the fixed bending dies of the rolling equipment can only form around and support the exterior of the material.  This leaves the center of the tube open, and more vulnerable to deformation due to uneven pressure.  Tubes can experience concavity, or even changes in overall height or width on particularly difficult bends.

Example of Slight Concavity in 16×12 Tubing Rolled the Easyway

This happens as a result of the rolling dies pressing inward on the tube walls.  The reverse pressure from the die on the opposite side of the material also pushes back, but the force does not carry through the hollow space of the tube equally, leading to issues of concavity and the resulting shift in material causes height and width shrinkage/growth if severe enough.

Bending Pressure

An available option to counteract these efforts is to increase the wall thickness of the tubing to help in lessening distortion issues.  In the event that material is architecturally exposed tubing, sometimes any deformation is unacceptable, and in those cases, further accommodations or changes may be required to the design to find an alternative.

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Short Radius Elbow, Sweeps & Returns through Pipe & Tube Bending

Many industries, including liquid petroleum gas (LPG), chemical & petrochemical, energy, and process piping, etc. have a large requirement for pipe fittings including elbows, sweeps and returns. These industries deal with the transferring of gases and liquids within their processing facilities and between one another on a daily basis. Elbows, sweeps and returns are used to make a connection between two straight lengths of pipe or tube when the direction of the piping needs to change. Elbows are generally described as a bend between 45deg and anything less than 180deg. Sweeps are gradual bends and usually described as anything less than 45deg of bend. And returns are just that, 180deg of bend; making a return to the direction from which it came.

These pipe/tube fittings are generally described in one of two different ways; short radius or long radius bends. Long radius elbows, sweeps and or returns are generally considered anything over a 3D bend but usually not exceeding a 6D bend. Short radius elbows, sweeps and or returns are usually considered to be anything under a 3D bend. The description of these fittings, i.e. 3D, 5D, 6D are directly correlated to the pipe/tubes diameter, where the number before the “D” is the amount you multiply the diameter of the tube/pipe by. For example, a 3D bend on a 2” tube would be a 6” center line radius (CLR).

Short Radius pipe/tube fittings can be made through a number of different processes including cold and hot forming but 2 of these are most common. The 1st of these processes to be considered and the most common of methods to obtain elbows, sweeps and or returns is rotary draw bending or as most people call it mandrel bending. Rotary draw bending is a precise technology as it requires a specific set of tool/dies for each pipe/tube diameter with a specified, consistent CLR. The Rotary draw bending process is usually done on smaller pipe/tube sizes up to and including 10” in diameter and can be done on nearly most metals/alloys including but not limited to, aluminum, stainless and carbon steel. This process is accomplished by drawing the work piece (tube/pipe) around a rotating die. The leading edge of the material to be bent is clamped to the bend forming die and a mandrel is set within the tube/pipe at a precise location so as to support the work piece from within to avoid collapsing or failure of the tube/pipe. The forming die is than rotated, causing the tube/pipe to curve around the die leaving the work piece bent to a specific radius. This process for bending is the most common, least expensive and quickest but its drawback is the amount of costly tooling that is required to keep in house in order to perform many different bends.

The other most common manufacturing process to consider when looking to achieve short radius elbows, sweeps, and return fittings is heat-induction bending. Induction bending is most common but not limited to large diameter pipe/tubing, taking over where rotary draw bending left off at 10” in diameter all the way up to the largest pipe/tube sizes they make. This method of bending is extremely time consuming and a certain degree of metallurgy know how is required as this process heats up the work piece between 800 and 2,200 degrees through the use of an electrical transformer in the form of a coil to achieve the bend. These machines are generally very large in size and the overhead cost to operate and maintain these machines drives the product cost up. The main advantages of heat-induction bending is that these machines do not require specific sets of radius dies; heat-induction bending can perform an infinite number of differing radii and can do so with minimal distortion if any. The major drawback besides the cost of the products produced by this method, is the material alloy type that can be used in induction bending is pretty much limited to that of carbon steel alloys as the induction heating process requires a ferromagnetic material that will generate eddy currents within, when electromagnetic induction is placed upon it.

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I’ll be Curved for Christmas

It’s Christmas time!  Lights are being strung from the roof tops of homes and businesses all around the country. It’s a beautiful sight.  In Kansas City we have a lighting ceremony at the historic Country Club Plaza, a shopping district built in 1922 which has the longest life span of any planned shopping center in the history of the world.  Christmas lights were put up on the buildings for the first time in 1925, and the tradition has continued to grow year after year.  The lighting ceremony signals the true beginning of the holiday season.  As magnificent as this is, I couldn’t help but notice the shape of the buildings now illuminated by lights.  Most all of the buildings are sharp cornered squares, and relatively the same with the exception of a tower and the varying heights.  As I moved northward there was such a contrast with the addition of the newer buildings in downtown such as the Sprint Center and Performing Arts buildings.  Each of these has curved outlines — one looking like a giant fishbowl and the other has a rooftop that looks like the waves of the ocean tide.  Many of the newer buildings have unique shapes and provide a much different, fun, and interesting Christmas lighting display.  These works of art are made possible through the use of curved steel which gives life to many ideas.

Country Club Plaza, KCMO
Christmas Lights at the Country Club Plaza, Kansas City MO
Sprint Center, Kansas City MO
Curved Steel Pipe Used at the Sprint Center Kansas City

Curved steel beams may be the foundation for many buildings which allow for a completely different architectural look than those of the past, but it was curved steel pipe that provided much support to the fish bowl shaped Sprint Center.  Curved pipe is used in so many applications you can find it everywhere if you just keep your eyes open. Curved pipe as handrails for circular staircases provide an ever flowing stream of Christmas lights for the homeowner lucky enough to have one, fencing around swimming pools, or a ribbon like railing around skating rinks lit up for the holidays.  Curved pipe can be found in pedestrian bridges or bank parking lots.

Round pipe seems to hold up well to the stresses of bending.  The very nature of its’ curved sides reduce some of the issues we encounter when bending other shapes.  When using metal pipe in a project you should always be aware of the possibility that with tighter radii the pipe may begin to oval.  This risk can be reduced if expectations are communicated in advance of production.  Aesthetically I think curved pipe makes the biggest statement as it has no sharp angles so it seems to flow in two separate dimensions.  There is the outline of the pipe itself along with the radius manipulated by the rolling process. With a little imagination, good planning, a few pieces of pipe, and a good rolling partner, we could have one of the most beautiful holiday lighting displays ever!

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Curved Steel to Help Uncage Big Cats

A zoo which is short for zoological park or garden is a facility in which animals are confined within enclosures and displayed to the public. Many critics believe that zoos hurt the lives of those they cage and they hurt our understanding of what animals and their habitats really are.  Zoos in America, particularly those with scientific societies, display these wild animals primarily for the conservation of endangered species, as well as for research purposes.  Secondarily, they are displayed for the entertainment and education of visitors. To address the critics concerns, the Philadelphia Zoo is opening a new extension.  Called Big Cat Crossing, it is a 2.3 million dollar investment consisting of both state and private funding. This groundbreaking animal travel and exploration trail system provides large felines- lions, tigers, pumas, jaguars- with more room to stretch their legs and roam broadly around the Zoo.  A local fabricator who teamed up with Chicago Metal Rolled Products was given the task of constructing a 330 foot pipe and mesh engineered passageway that would extend 14 feet above the Zoo’s main visitor path, encouraging felines to explore overhead.  The pathways base frame is made out 85 feet of carbon steel 12” schedule 40 pipe curved to radiuses ranging from 110ft to 30ft. The tops of the passageway structure will have 38 overhead hoop rings that are constructed out of hot rolled 3” schedule 40 pipe curved to 2ft- 8 ¾ inch centerline radiuses. The big Cat Crossing is designed to be 4ft tall and range from 3ft-4in to 5ft wide at different points in the trail, offering enough room for the animals to move comfortably through the trail system. Philadelphia Zoo is the first to implement a campus-wide animal travel system, designed for a wide variety of species and affording them the opportunity to move more broadly around the Zoo. The curved pipe overhead trail is sure to fuel the curiosity of the Zoo’s big cats and educate its 1.2 million annual visitors about the endangerment of big cats and opportunities to get involved in species saving initiatives.

Big Cat crossing at the Philadelphia Zoo
Big Cat Crossing at the Philadelphia Zoo

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