Types of Steel Sections — The ‘Alphabet’ or ABCs of Structural Steel
Structural steel is an important building material that consists of three shapes: angle, beam, and channel (sometimes referred to as the ABCs of structural steel). All three have unique cross-sections and mechanical properties and require specific ways to accurately measure them.
A: The architectural steel angle beam or ‘L-shaped beams’
Angle beams or ‘L’ shaped beams are hot-rolled products. The rolling process leaves it in its familiar ‘L’ shape. The two ‘sides’ of the ‘L’ are called legs. Angle beams consist of two legs that come together, meeting at a 90-degree angle. The leg sizes may or may not be of equal size, depending on the requirements. This splits the L-shaped beam into two camps: equal and unequal.
Angle beams are often used for:
- Structural reinforcement
- Structural steel brackets and cleat connections (equal-legged angles)
- Lintels and floor systems (unequal angle beams)
The rounded inside angle is called the fillet (pronounced “foe-lay”) and the radius of the fillet is called the fillet radius. Knowing the size of this radius is important because it will have a big impact on the practicality and function of the angle beams, depending on how you want to use them.
B: Structural beams: ‘I beams” or ‘H beams’
The word ‘beam’ can have many different meanings. Traditionally, a beam referred to a solid piece of timber. In building construction, a beam is like a mini bridge in a structure that carries a load. The load may be a brick wall or the floor or roof of a building.
Structural beams are referred to as either I beams or H beams because of the shape of their cross-section. Both H and I beams are capable of resisting shear forces and are extremely resistant to bending. The flat, horizontal sections of the beams are called flanges. The middle, vertical part that connects both of the flanges is called a web.
- The function of the web is to resist shear forces that may cause breakages or collapses
- The flanges are there to resist bending movements.
I beams also have multiple fillets where the web connects in a curved angle with the flanges.
Confusingly, structural beams have many different names:
- ‘W’ shaped beams (especially if they have larger flanges)
- Universal beams
- Rolled steel joists (RSJ beams)
I beams, H beams or W beams — whatever you want to call them — are commonly used for structural support in construction. In this case, it is very important to have a professional choose the right beam in order to support the load. Knowing how ‘deep’ (beam depth) the beam is, and how wide and thick the flanges are, along with the thickness of the web, will help you to determine if a beam is strong enough to support a load.
There are also two types of beams: universal columns and universal beams. Universal columns are roughly about as wide as they are deep (tall). As a result, universal columns are the most frequently used section for construction. Their small depth makes them ideal for load-bearing when the height is limited.
Universal beams often have a depth much greater than their width. Universal beams have several advantages, such as a higher loading capacity. However, space can sometimes be an issue in construction, and so universal columns are used instead.
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C: The architectural steel channel or ‘C channels’ and U channel steel
Structural steel channels are hot rolled products that have a C-shaped cross section. They consist of two legs connected by a web.
Here are some important things about structural steel channels that you should keep in mind when looking at them:
- The ‘depth’ of the channel (how tall it is)
- Leg height
- The thickness of the leg
- The thickness of the web
- The fillet of the C-channel. The fillet is the angle where the leg meets with the web. This radius is not always provided
There are various types of steel channel categories:
- Structural channels, which are common in construction and manufacturing
- Ship and car channels, specific for those industries
- Stair casting channels, for constructing stairs
- Bar channels, these are usually much smaller than typical C-channels, for specific uses
Like with structural beams, these structural steel channels have lots of different names. They can sometimes be referred to as ‘hot rolled parallel flange channels’ or just ‘flange channels’, or ‘channel beams’, or ‘PFC sections’ in addition to just being referred to as a C shape steel beam.
Channels with longer legs take on a U shape, and so are called steel U channels or U section steel channels. They are virtually the same as a typical steel c section; only the longer leg length gives the steel u-channel its alphabetical namesake.
The channel is often used for columns, and lintels above doors to give support to floor joists. If you are using a channel as a lintel it will need a bottom plate added to it to take the outer bricks. Alternatively, two channels could be fixed back to back to support both leafs of a cavity wall.
P: PFC sections
A PFC section is just another name for a C-shaped (or even U-shaped) steel section. They are typically used as columns or as support for floor joists and are considered to be an essential load-bearing profile.
See the above section (C: The architectural steel channel) for more details.
R: RSJ beams
What is an RSJ beam? The simple answer is: an RSJ beam stands for ‘rolled steel joist’. They act to support a load and are often used in construction. There are many factors involved in building, and usually, a structural engineer will determine if an RSJ support beam is more suitable over other forms of supports, such as timber or concrete beams.
‘RSJ beams’ are another way of referring to I beams, H beams, and other types of structural beams (see the ‘B’ section above for more information).
T Sectional Steel (or tee beams)
T beams can withstand large loads. They get their shape (and name) from the fact that they do not have a bottom flange.
Steel t-sections are often used in steel roof trusses to form built-up sections. The lack of a bottom flange is cost-effective in terms of needing fewer materials, but there is a trade-off. T beams are not as strong as their I-beam equivalents.
T section steel is also sometimes referred to as just a ‘flange beam’ or a ‘web and flange’ or even a ‘flange and web’ beam. All these names highlight the fact that it is “missing” a second flange, which is typical of I beams.
RHS Steel Sections (RHS meaning ‘Rectangular Hollow Sections’)
RHS steel sections are just one of three types of popular steel hollow sections. RHS beams are popular in mechanical, structural and construction applications because they typically have a very flat structure that makes it more economical for welding, joining, and various other types of fabrication work.
In short, what is RHS? RHS beams are a type of rectangular steel tubing. They only need to be straight cut when joined to other flat services. This makes the RHS section very popular, as very little welding and joining preparation is needed. They are also used to glam up the look of a building, as they are very straight and smooth, as well as strong.
The rectangle shape is quite hard to bolt. For this reason, it is not as common as the universal columns (see above). It is hard to bolt and to bolt other members or beams to it. There are two types of RHS steel: ‘hot’ and ‘cold’. Hot rolled RHS sections consist of one piece, right off the mill. Cold-formed RHS sections need welding together and are not made in one piece.
SHS Steel (SHS meaning ‘Square Hollow Sections’)
Square hollow sections are another popular type of structural steel tube. They are a kind of intermediate between RHS steel tubing and CHS beams in terms of appearance and structural behaviour. Square section steel also has a flat surface and clean lines — which both make welding and joining very economical.
Square section steel often provides the ideal balance between strength, aesthetic appearance, and being functional. These three reasons are why square metal tubing is still so popular to this day. But like the RHS sections, steel tube squares are difficult to use. It is hard to bolt them to beams. Square steel tubing also comes in ‘hot’ and ‘cold’ forms. Another name for them is a “box section”.
CHS Steel (CHS meaning ‘Circle Hollow Sections’)
Of all the steel hollow sections, the circular hollow section came first. The CHS section is a common feature in a wide variety of structural steel operations and has a lot of construction and mechanical uses. The consistent and clean lines of steel CHS make this circular tube a very aesthetic choice in many building designs.
CHS steel is popular for the construction of handrails, balustrades, and scaffolding. Other purposes include sign poles, columns, fences, and architectural features such as bending steel staircases. CHS can be fine-controlled and internally scarfed. This allows the tube to be suitable for mandrel bending.
Steel Flat Bars (Metal flat bars or ‘Flat Sections’)
Steel flat bars are one of the most basic of building materials. Flat metal bars are practical anywhere a connection between two beams is required. Flat steel sections are commonly used as:
- Base plates
- End plates
- Stiffeners (secondary plates)
- Splice plates
When a flat section is cut into smaller pieces it is called a flat steel plate. Flat sections are often used to strengthen other beams and are sometimes used to reinforce timber joists. That is why it is so typical to see a flat steel bar with holes in it, ready to be bolted in place.
Steel structures are structures assembled from the various steel sections listed above (see the ‘Types of Steel Sections’ section for more information). There are many types of structures in architectural steel and some of them resemble ‘everyday’ objects — such as goal posts.
Steel structures are made from bolting the different types of steel sections together to achieve a particular function, either by bolting, welding, or riveting and more. A steel structure, by the simplest definition, is just an assemblage of steel sections that can safely withstand a load.
Steel structures have countless functions and are everywhere in society. Here are some places you will expect to find steel structures:
- Transmission line towers
- Railway platforms
- Industrial buildings
- Oil and gas storage tanks
- Tall residential building frames
- Lamp posts
- Stadium roofs
Goalpost steel structures
Goalpost beams get their unimaginative names from their shape. When two columns and a crossbeam (usually acting as a lintel beam) come together, it looks like a goalpost.
Goalpost beams are often used where the foundations can be dug and cast in concrete (such as rear extensions). Goalpost beams are very sturdy. If a project requires a large aperture (an opening or hole) then goalpost beams are ideal. Their columns are well-designed to dissipate the load.
There are a few different types of goalpost steel structures:
- Goalpost with crossbeam — A crossbeam is a beam placed between two walls in a structure; in most cases to support the roof of a building. A goalpost beam is often used with a crossbeam if the crossbeam has replaced something in the existing structure.
- Goalpost with 2 crossbeams — If two walls need supporting, it may be necessary to use a goalpost beam along with two cross beams.
- Two goalposts with crossbeams — Take two walls out, and there can sometimes be load issues. Two goalposts and a crossbeam provide a structurally-sound solution to support remaining walls. In some instances, the crossbeam can be used to support a fireplace.
The cross beam
As its name suggests: a cross beam is a type of beam that runs ‘across’ a structure, carrying its load. This is in opposition to other ‘beams’ that support a structure upright. In mechanical engineering, this can be a little confusing. There is little differentiation between a beam and a crossbeam. Even dictionary definitions can sometimes refer to a ‘beam’ as horizontal support.
A crossbeam is typically made from a steel I-beam, and is able to support an enormous amount of weight over a very long timeframe.
There are a few different types of crossbeams that function as steel structures:
- Crossbeam with two beams — This metal structure is particularly good at supporting chimney stacks. The cross beam takes the bulk of the weight, while the parallel beams span the sides of the room. A top plate is sometimes added to distribute the weight of the chimney.
- Crank with crossbeam — If there is a ceiling, there’s likely to be a crank with a cross beam. This structure is adept at supporting roof joists.
- Crossbeam with mid support — If the load of a crossbeam is in need of support, then a mid-support column is usually the answer. Mid-support columns usually need to fit in-between windows, doors, and other walls.
Other types of beam structures
Beams support loads by bending (a process known as ‘flexure’). There are many different types of beam structures. Each slightly modified to accommodate the dynamic world of architectural steel.
There are many different types of ‘other’ beam structures that don’t involve crossbeams:
- Apex beam — This structure gets its name from its double-cranked shape. The two cranks draw on the main beam for strength. Often the apex beam is the structure of choice in floor renovation.
- Post with steel support beam — A post with a beam is often used for extra support. Typically this is when one beam has the support of a load-bearing wall and the other does not.
- Beam with mid support — Sometimes the load on a beam may be too high. In such instances a post will add extra support, taking the weight off the beam. In general construction, the post’s final position will depend on the layout of the room, so it may not always technically be ‘mid support’.Beams with mid supports are a common sight on large bridges. In these circumstances, they are sometimes referred to as a continuous beam.
- Corner beams with post — Corner beams with a post are mostly utilised to strengthen both rear and side walls. They are common structures in building extensions.
Steel box frames
A steel box frame is a square-shaped steel structure, made when four beams come together. Steel box frames are common when there are steel beams running parallel in the side walls; one on top and one on the bottom, with two supporting beams at the sides.
There are many different types of steel box frames:
- Box frames with crossbeams — A crossbeam is a beam placed between two walls in a structure; in most cases to support the roof of a building. A box frame is often used with a crossbeam if the crossbeam has replaced something in the existing structure.
- Box frames with a steel support beam and post — A steel post may be necessary if there is nothing to support the box frame after construction. In the absence of a load-bearing wall, the burden shifts to the post and its foundation.
- Steel box frames with a perpendicular box frame — If the load is particularly heavy, then a post on its own may not be enough to carry the weight. In such instances, a bottom beam is usually added: that connects the post to the foundation of the box frame. This serves to spread the weight around, shifting the burden from the post.
- Two box frames with a crossbeam — In some instances, a structure may need two box frames joined with a crossbeam. For example, it is not uncommon for a wall to be ‘knocked down’ to create a larger living space. With the wall gone, a crossbeam is sometimes needed to manage the load.
- Steel box frames with extended beams — An extended beam is often used when there are space limitations and a column is not an option. The extended beam distributes more of the weight. Box frames with extended beams are often used in the corridors of large buildings.
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Steel Connections and Steel Joints
Steel connections are quite literally what holds everything together, the steel frame connections of structural steel. There are various types of steel beam connections and steel joints.
Steel base plates
Steel base plates are what supports a column on its foundation. For stability and lasting power, it is essential to fix a base plate about 20mm above the concrete around the column. Wedges and metal shims can force open a gap, which is then filled with dry-pack (a type of concrete).
An end plate is much like a base plate but acts as an anchor to a wall, not the floor.
End plate connections
Like its name suggests, end plate connections help connect two points. This may be two beams or a flange.
In construction, the term ‘moment’ refers to the amount of stress on a joint. Moment resisting connections are there to help reduce the pressure a joint may be under. An overhanging plate bolts into both columns, reinforcing its strength.
A cleat plate bolts two beams together (though in some cases it may be preferable to weld the cleat plates, depending on the circumstance). It provides strength and reinforces connections at the beams.
Spacers are sometimes made of concrete, metal — even plastic. The spacer reinforces the steel by keeping it in place. This is important for the final pouring of concrete into the structure.
Spacers have many different names, such as rebar spacers, reinforcement spaces, mesh spacers, and so on.
Spacer beams are often used to bolt two beams together, giving both rigidity and security.
A PFC space — as the name suggests — is often used for a beam to beam connection, usually to bolt two PFC beams. (A PFC stands for ‘Parallel Flange Channel’.) After bolting two PFC beams back-to-back, a PFC spacer is there to give strength to the walls.
What is a cranked beam? The simple answer is: a cranked steel beam in an angled beam with two kinks in it, making a 90-degree angle. The main function of a cranked beam is to support roof structures — so they need to be welded extra tight. This process is called full penetration welding and is necessary to carry the load of roof tops.
Crank beams are also sometimes used on stairs, and especially if the stairways are expecting to carry heavy loads. There are several types of cranked steel beams:
A characteristic crank with two notable kinks. Ninety-degree cranks support roof structures. Supporting the roof is very important. Thus, it is important to conduct full penetration welds when manufacturing these cranks. A penetration weld is a weld that penetrates fully from the roof of a joint (top) to the cap (bottom).
A ninety-degree kink is the basic shape of two sections welded together. These kinks are common in brackets and to bolster support for columns.
This angled kink follows the shape of the roof. It reduces the load burden on the crossbeam. It can do this without the need for extra vertical support columns.
Kink with plate
A plate is necessary for a kink angle if the connections are of different sizes. The plate allows the two sections to join together.
Dogleg cranked beams
A ‘Dogleg’ beam is a horizontal beam with a vertical section welded at 90°. This type of beam resembles a dog leg kicking out. It is often used to support existing staircases.
Structured gallows brackets
Structured gallows brackets are almost as out-dated as the medieval torture brackets that they get their names from. They were popular for a time from the 1800s onwards as a way to support numerous structures, such as chimney breasts. Nowadays, RSJ beams tend to be preferred to structured gallow brackets.
Like many other types of structural beams and steel connections, the gallow bracket has various different names: such ‘chimney support brackets’, load bearing gallows’ and ‘structural gallows brackets’.
Plates are the joining forces of the architectural steel world. They are often the last part of the construction puzzle designed, yet one of the first installed. They are often made from the cutting of flat sections and then welded to joists.
Gusset Plate (a triangular gusset plate design)
Gusset plates are triangular-shaped. This shape affords an extra sturdiness to the structure. In many cases, gussets act as extra support for bottom plates welded to a beam.
Bottom plates give beams that extra support to keep brickwork and timber joists in place. Bottom plates often ‘stick out’ under the beam. This is to make sure the support is adequate.
A top plate, like the bottom plate, is there to increase support for the beam. Top plates are sometimes used if the size of the required beam is smaller than the wall it is carrying.
Stiffeners are secondary plates or sections that are attached to a beam’s webs or flanges to stiffen them; this helps to provide extra stability and prevent buckling. They are sometimes referred to as web stiffeners as they commonly attach to the web of other beams.
If a column section needs anchoring to a wall, which is where a tab comes in. Tabs are welded in a staggered formation to column sections to give them an extra rigidity.
Holes are often drilled strategically in architectural steel to bolster support and structure.
Flange holes are an alternative to using tabs (see above section for more information about tabs). As the name suggests, flanges often have holes drilled into them for extra rigidity.
Web holes are ideal for fixing timber joist hangers to beam joists. This is often necessary for the laying of floor joists.
Splice plates are types of metal joining plates that exist to join two members end-to-end in construction. Splices come into force if the existing structural elements require longer lengths not available. They ‘bridge the gap’ in effect, to compensate for this lack of availability. As a result, they are sometimes known as splice connections.
Splice plates are labelled depending on the connection they are used for. The following letter and number combinations A1, A2, A3 and B1, all denote specific types of connections:
An A1 splice plate is required when a beam spans two party walls for ease of installation, or, when a beam is either too long or too heavy to install.
If the splice connection requires extra, inner flange plates, it goes by the name ‘splice A2′.
A3 splice plate
Is used to align two sections and would need additional support either with a column or pad stone.
The splice B1 is a good choice in space-restricted areas. It is not a full splice, and so maybe unsuitable in some applications, but it is a considerable space saver.
Metal finishes help to prevent rust. Rust is the end-process of a chemical reaction. And although ferro-alloys are added to steel, it is not always enough. When moisture and oxygen come into contact with steel, molecules join to form iron oxide. This makes the metal weak, corrosive, and useless.
The slowing or prevention of rust is big business. Because so much of the world uses iron and steel, it is of major importance to keep our architecture healthy.
Priming (Primed Steel)
A primer is a coat added to steel to stop it rusting. This is usually done before painting the steel. It is common in maritime, and highway and infrastructure industries.
The primer itself is often a ‘paint’ of resin, additives, and solvents. Some primers even contain plastic polyethene. Primers keep painted steel fresher for longer because the primers used help the paint-coatings stick around.
Galvanising (Galvanised steel)
Galvanising is the process of applying a zinc coating to steel. A bit like with stainless steel. This can protect the steel from atmospheric corrosion for more than 30 years. There are two general applications for the zinc coating: hot dipping and electrolytic deposition.
The zinc coat often ‘sacrifices’ itself to keep the steel intact, as the chemical makeup of the zinc makes it more likely to corrode. Galvanising is a common and essential part of steel fabrication, especially in the cladding industry. It is very useful for keeping steel intact, especially in external and damp areas. But also for inside walls susceptible to where moisture can enter.
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