Beam Tolerance After Rolling

Curved beams are used everywhere – in structures for functionality or aesthetic appeal, in circular shell stiffening rings on vessels and for monorails or roof trusses. Beams can be curved vertically (the weak-axis) or horizontally (the strong axis). When curving beams, it is important to consider distortion.

Distortion is any deviation from the original cross-sectional shape that usually occurs in every bent member to some degree. Think about curving a straight piece – the curving process is distorting the original shape to a curved shape. The potential for distortion is dependent on several factors, including the bend radius, the thickness of the material, the dimensions of the beam, bending axis, bending method and initial material geometry imperfections from the mill.

When a steel beam goes through the bending process, it is strained past its yield point which usually causes some level of cross-sectional distortion. The procedure creates inelastic compression stresses in the steel that can cause cross-sectional distortion. Distortion is the product of localized contact forces where the rollers of the machine contact the steel beam.

When rolling a beam the hard way or over the strong axis, complete an inspection both before and after rolling to ensure quality. This includes checking that the straight beam applies to AISC mill tolerances. Check the beam to ensure the flanges are perpendicular to the web using a framing square. With the beam flanges sitting on a level floor, check for gaps between the flanges and the floor. Gaps indicate sweep from the mill.

On very critical radius parts, the inside rolling radius must be maintained and fit to a scribe line. The rolling radius tolerance should be specified by the customer (e.g., +/-1/8” from the scribe line). The minimum length tolerance of the rolled section should be measured along the outside radius surfaces using the theoretical outside arc. Rolled sections must allow 4” minimum extra length for fabrication or field trim. The sweep tolerance is usually specified by the customer (e.g., 1/8” on a 36” section). The flange out of square tolerance should also be specified by the customer, (e.g., +1/8/-0”).

Here is a quick overview of tolerance checks on a hard way rolled beam:

  • Radius tolerance (+/-)
  • Minimum length, outside arc (+)
  • Sweep tolerance with 36” template (+/-)
  • Max out-of-square (+1/8)
  • Flange Offset (+/-)
  • Flange Warpage & Tilt (+/-)

 

 

 

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Aluminum Stair Stringers for a Helical Staircase

Early in January 2017, a company from Puerto Rico gave us a call to talk about the aluminum stair stringers for their helical staircase. The company was planning to make a helical staircase for ‘Birth of a New World’, a Christopher Columbus sculpture made by Zurab Konstantines dze Tsereteli. Tsereteli is a famous Georgian-Russian painter, sculptor, and architect known for large-scale and at times controversial monuments like the ‘Tear Drop Memorial’ pictured below, located across from Liberty Statue in New York City.

Tear Drop Memorial
Tear Drop Memorial

The Christopher Columbus ‘Birth of a New World’ statue was originally intended to be a donation to the United States to mark the 500th anniversary of Columbus’s landfall in 1492. After being turned down by several US cities, including Columbus, Boston, Cleveland, Fort Lauderdale, Miami and NYC, the statue was finally offered to Puerto Rico where Columbus arrived in 1493.

Birth of a New World Statue
“Birth of a New World” Statue

After this little history briefing, let’s discuss the details of the aluminum stair stringers used for the staircase leading to the ‘Birth of a New World’ statue. The staircase is in the center of the statue and spirals upwards. The statue itself is located by the ocean. In order to avoid corrosion issues, the customer chose to use a 10-inch aluminum channel made out of 6061 aluminum. This represented a challenge given the characteristics of forming aluminum stair stringers. Following CMRP’s engineering recommendation, the aluminum material thickness was increased to 5/16 help prevent deformation of the flanges.

Another big challenge in this project was the placement of the stair itself.  The circular wall within the statue was only 6-feet in diameter.  Within this space, the customer needed to fit an inside and outside aluminum stair stringer, going up 3 floors, each 13-feet high.  That implied an inside stair stringer with only 2-foot 2-inch internal radius with 52° of pitch.  In addition, outside stair stringer would run only 1-inch away from the concrete wall which required extremely accurate rolling/forming operations.  The job being all the way in Puerto Rico would give us no room for inaccuracies, the aluminum stair stringers had to be perfect.  As you can see from the pictures, they were!

"Birth of a Nation" Staircase
Helical Aluminum Stair Stringer
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Sheet Metal Rolling

Before we disscuss sheet metal rolling, let’s first get a few basics about sheet metal:  what is it; how it’s made; how it’s designated; and how it can be used.

Sheet Metal is a metal being formed by an manufacturing process into thin, flat pieces. The sheet metal rolling process consists of passing metal stock through one or more pairs of rolls to reduce the thickness and to make the thickness uniform.

Sheet Metal Forming Between Rolls
Sheet Metal Forming Between Rolls

To determine the designation of sheet vs. plate in general terms we can say that anything 1/8″ and thicker is a plate and anything less than 1/8″ is a sheet. The thickness of sheet metal is normally designated by a non-linear measure known as gauge. The larger the gauge number, the thinner the metal. Commonly used steel sheet metal ranges from 30 gauge to about 6 gauge.

Sheet Metal Gauges
Sheet Metal Gauges

Sheet metal can be available in flat pieces or coiled strips. It is one of the essential shapes used in metalworking. Innumerable everyday objects are fabricated from sheet metal. Sheet metal can be cut and bent into an unlimited number of applications like: ductwork, machine guards, other machine components, architectural column covers, wall coverings and downspouts, tank bodies, just to name a few.

There are multiple manufacturing process that sheet metal can be formed by: bending, curling, incremental sheet forming, laser cutting, perforating, press brake forming, punching, roll forming, rolling, spinning, stamping, water jet cutting.

As a metal rolling company we have been rolling the Sheet Metal since our conception in the 1908. We specialize in rolling of lock-seam pipe, welded pipe and open-butt-joint pipe out of carbon steel, stainless steel, brass, copper and other alloys including aluminum. We can also roll sheet metal in to other shapes.  Contact Chicago Metal Rolled Products for fast and accurate quotes on rolling sheet metal.

Rolled Sheet Metal Shapes
Rolled Shapes from Sheet Metal
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Metallic Bonding and Distortion in Curved Steel

When describing cross sectional distortion of cold-formed steel members the term fluidity can from time to time be observed. This might rattle most people’s logic, as steel is a well-known solid. It is not that structural steel exists both in solid and liquid state simultaneously during cold forming, but rather that when a stress great enough to yield a member, is applied to that member through a bending moment, steel members display fluid like characteristics in the form of flow. This is commonly seen in wall thinning and thickening and or a reduction in the cross section of a member. To explain how this is possible it is necessary to have a working knowledge of steel and ultimately steel’s base metal, iron (Fe), on the molecular level.

Steel is an alloy or a mixture of Iron and Carbon with other elements working as additives to alter the chemistry and enhance certain properties and or characteristics of the steel.  Iron, steel’s base metal is the most common element on earth. Pure it is relatively soft and not very strong but its interaction with carbon makes it one of today’s most utilized materials. When we speak about the cold forming of steel and how during that process steel displays fluid/flow like characteristics; we must strongly consider steels’ base metal, iron. When Iron starts solidifying from liquid state it does so in crystalline form; meaning that at the molecular level, iron atoms arrange themselves in a lattice type structure. The bonds formed between iron atoms are the key to the fluid/flow like characteristics that steel display when under stress. Metallic bonds unlike covalent or ionic bonds (where two atoms share one electron or one atom takes an electron away from another atom to form a bond) share their valance electron over the entire lattice structure of atoms, known as a delocalization of the valance electron. This is important, as this type of bonding allows for iron to be malleable meaning it can be shaped; it also allows for iron to be ductile meaning it can be stretched and drawn. These fluid/flow like characteristics are types of plastic deformation. The delocalized sea of electrons acts like a bonding blanket encompassing the iron lattice structure, keeping the lattice bonded but allowing the atoms within the lattice structure to move or slip without breaking bonds. This dislocation or slippage of the lattice structure is considered to be a linear defect of the iron crystal. But this defect in the iron crystal is not a bad thing in the sense of the word, but rather is what makes plastic deformation even possible. The ease of movement of these dislocations is what determines the material’s strength and yield. Any obstruction or defect within the lattice structure makes slippage/plastic deformation more difficult; even the slippage of dislocations make plastic deformation more difficult. Dislocation of slip planes create other dislocations that obstruct the movement of dislocations, this is known as work hardening.

Steel comes into play in all of this when you add a percentage of carbon to the iron mixture. As said before pure iron is rather soft, displaying flow/fluid like characteristics in the form of malleability and ductility but ultimately it lacks the strength one would seek in a building/construction material. Add 0.12-2.0% of carbon into the mix and iron becomes the material we know today as steel. As iron and carbon are heated the lattice structure of iron changes and rearranges on itself. These different forms of lattice structures are known as allotropes. The allotropy of iron is extremely important as these allotropic formations, when heated to certain temperatures, interact with carbon in different ways. Through substitution, this allows the carbon atom to join the lattice structure. It is this positioning of the carbon atom within the lattice structures that gives steel its strength and toughness. To a certain extent increasing the carbon content within the alloy steel mixture will increase strength and hardness of the material. But in general it is the hardenability of the steel alloy mixture that is increased, as making steel harder is generally achieved through heat treating and cooling times which either allows or prevents the carbon atom to escape or diffuse from the lattice structure. Add too much carbon to the mixture and the material gets harder but less tough as the material cannot absorb energy efficiently and the material becomes brittle and susceptible to cracking. Ultimately, it must be thought that when bending/forming i.e. plastically deforming steel members we are really deforming the slip planes/dislocations of the iron/carbon molecular lattice; and that the carbon atoms placement within the lattice structure prohibits the slippage of the dislocations to a certain degree, making steel harder and stronger than its base metal, iron. Now of course in the steel we know today there are many other elements added into the mixture to assist and enhance certain characteristics like hardness, toughness, stiffness, etc. but carbon is the major alloying element that makes iron the material we know today as steel. Many of steels attributes including those that display fluid/flow like characteristics can be attributed to steels base metal iron and its metallic bonds.

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Super Solar Canopies for Super Bowl LI at NRG Stadium

On Sunday, February 5, 2017, also known as Super Bowl Sunday, millions of football fans and others will watch the Atlanta Falcons battle the New England Patriots to see who will be Super Bowl LI Champions. Though most of us will watch this battle on TV, a capacity crowd of 71,795 fans will gather at NRG Stadium in Houston, Texas to watch this game live. Continue reading Super Solar Canopies for Super Bowl LI at NRG Stadium

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Curved Beam Design Procedure

Form plus function almost always results in a great design. Architectural design in addition to engineering design represents each of the variables in the equation for a successful design solution. The architectural aspect of a curved beam design achieves ideal appearance and functionality. A design that has been well engineered produces an efficient and capable performance solution. Continue reading Curved Beam Design Procedure

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Giant Size NFL Helmets

The 2016 NFL season recently kicked off in September. With successful baseball and hockey teams, Chicagoans are hoping that the Bears will take home a few more wins this year. While we keep our fingers crossed for the Bears this season, we are flashing back to last April when Chicago proudly hosted the 2015 NFL Draft at the Auditorium Theatre.

The city was buzzing with fans supporting their football team during the draft. One popular spot was Pioneer Court, an open area along Michigan Avenue that housed 32 giant NFL team helmets during the draft for fans to take pictures with. Continue reading Giant Size NFL Helmets

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Welded Connections of Curved HSS Members

The welded connections of rolled HSS members of differing wall thickness and radial geometry must be considered by the construction team prior to the rolling, fabricating and erecting of the HSS members. This is due to the ungoverned consequential cross-sectional distortion of curved HSS members from the rolling/curving process. wThe issue exists in the fit up when trying to make welded connections between two of the same HSS members where one member is curved and the other member is straight or where both members are curved but their wall thickness and radial geometries differ. The cross-sectional distortion of curved members is a constant issue for bender/rollers that differ from process to process and from piece to piece depending on desired geometry and wall thickness. This cross-sectional distortion could be seen as ovality and/or a reduction in diameter in Circular Hollow Section (CHS) and an increase or reduction, known as shrinkage or growth, of the cross-sectional dimensions in Rectangular Hollow Section (RHS) and Square Hollow Section (SHS). The resulting reduction/growth in cross-sectional dimensions happens as a result of an attempt to eliminate localized buckling of curved HSS members, known as concavity and or rippling.  Bending companies are able to restrict concavity/rippling to a certain degree through the use of tooling but it is usually the case that the restriction of buckling in combination with the extremely high pressures used to favorably yield the material to achieve the desired geometry, has caused a change in the cross-sectional dimensions of the curved HSS member. This is an issue that is easily overlooked but could wreak havoc on a project if not considered early on in designing and detailing.

Continue reading Welded Connections of Curved HSS Members

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ACE Mentorship Program

Architecture, Construction, and Engineering are three of the most highly technical and collaborative professions you can pursue an education in today. The design and safety standards that are developed and continuously reviewed are some of the most widely respected standards you will find in any country or industry. These professions aren’t only responsible for future infrastructure and building projects, but also help to retrofit, rehabilitate, and respond to emergency situations regarding existing structures, aiding to prevent the risk of collapse or failure due to age or natural disaster in any region of the globe. It takes a technically proficient and capable individual to produce the high-quality work expected from firms that have established reputations in the industry for these necessary services.

Continue reading ACE Mentorship Program

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