The definition of steel structure
When it comes to building types, choosing the most future-proof type beforehand is the obvious choice. As such, steel structure is the type of building you’re looking for, performing better than any other possible structure type – concrete, timber, and so on.
Steel itself is an alloy of two material types – carbon and iron. Steel can also be infused with special properties by adding a number of additional materials in small percentages, be it sulfur, chrome, nickel, phosphorus, manganese, etc. This allows for several different varieties of steel to be produced. For example:
- Adding copper allows for better corrosion resistance properties of steel;
- Higher yield strength and tensile strength can be achieved by adding manganese and carbon, although there are two downsides, as well – the end result is harder to weld and has lower ductility (metal’s capability of extending by drawing without fractures);
- Both corrosion resistance and high-temperature resistance can also be boosted by adding nickel and chrome;
- Fatigue strength and the ability to weld can be improved by adding sulfur and phosphorus to the mix.
By its nature, steel structure is a structure made of multiple components connected with each other – with each component being created out of structural steel. Structural steel, on the other hand, is a steel-based construction material fabricated in a specific shape and composition to fit the necessary specifications.
There’s a massive selection of different steel sections that can be used as parts of a steel structure, with different shapes, sizes, and more. Some of the more common shapes that are used as steel structure materials are:
- Angle – a cross-section shaped like a letter “L”
- Sheet – a thin, flat piece of metal, usually 6 mm thick or less
- Plate – a thicker variation of a sheet, thicker than one-fourth of an inch
- HSS/SHS – Hollow Structural Section, or Structural Hollow Section, is a shape that includes circular, rectangular, elliptical, and square sections
- I-beam – a cross-section shaped like a letter “I”; a wide term that includes different kinds of beam types depending on the country:
- In Europe – a wide variety of sections, such as HL, IPE, HD, HE, and so on
- In the US – H sections, W-shapes, etc.
- In Britain – mainly UCs and UBs (Universal Columns and Universal Beams)
- Structural channel – C cross-sections/C-beams
- Rod – a long and relatively thin steel piece
- Z-shape – half a flange in different directions, closely resembles letter “Z” with its composure
- Tee – a cross-section shaped like a letter “T”
- Rail profile – a variation of I-beam that is asymmetrical in its nature, includes at least four different variations:
- Vignoles rail
- Grooved rail
- Railway rail
- Flanged T-rail
While some of these variations are made by welding together either bent or flat plates, the majority of the examples above are created with either hot or cold rolling – passing metal stock through pairs of rolls to make them less thick.
When built right, this structure is supposed to provide fully rigid contraception capable of supporting massive weights. Some of the building types that are using steel structures right now are bridges, towers, pipe racks, high-rise buildings, industrial buildings, infrastructure elements, and more.
Benefits and disadvantages
As with any other type of building, steel structure constructions have their own problems and benefits. Starting with the positive, steel structures’ advantages are quite numerous:
- Steel structures have all of the advantages of both mass production and prefabrication, with a few exceptions;
- Strengthening steel structures at any point in the future is a possibility, which works towards a prolonged lifecycle;
- Ductility – a property of steel to undergo plastic deformation before failing completely, improving reserve strength;
- Great fatigue strength;
- The overall speed of construction when using steel structures is impressively high, which allows for decreasing the spendings that you’ll usually have with prolonged construction jobs;
- Steel, in general, has an impressive strength-to-weight ratio, which makes structures themselves to be relatively light in comparison with the amount of weight they can hold;
- A lot of steel properties can be predicted with relatively high accuracy, making it far easier to calculate potential stress levels and other important criteria.
Of course, there would not be a market of multiple choices if one was a perfect fit for everything. As such, steel structures also have their own potential disadvantages, such as:
- Fireproofing steel structures is a necessity since intense heat is capable of drastically decreasing the overall strength of steel;
- Corrosion is also a massive factor when it comes to steel, in general, and steel structures are not exempt from this rule – especially when it comes to exposing such structures to water and air (bridges, mostly), hence regular maintenance and corrosion treatment is needed;
- Steel structures are often more expensive than other structure types, which makes them a far less attractive choice for smaller projects with a limited budget.
Types of steel structures in the form of buildings
There are many different examples of steel structures that we’ve provided above – and all of them can be split into four main types of structures. Each of these structures has its own approach to building and only works for specific types of steel structure constructions. As such, these four steel structure design types are:
- Portal frame. The most common type of light steel structure, a portal frame is a widely popular type of steel structure that relies only on section steel, steel pipes, and C/Z steel to withstand the force of the entire structure. It is often used for many different building types, be it industrial, agricultural, institutional, or commercial – although, the most popular example might just be the regular warehouse-hangar that is a common occurrence for many different countries all over the world.
- Steel grid. Generally speaking, a grid is a spatial structure that is comprised of multiple rods connected to each other in a specific form. There are many grid types out there, and many different standards for them, as well. They are highly rigid and provide extensive seismic resistance, which makes them perfect for hangars, exhibition halls, gymnasiums, and so on.
- Steel building frame. Another popular structure type that is mostly used for various multi-story buildings is the steel building frame, which consists of columns and beams that form structures capable of withstanding both vertical and horizontal pressure. A common choice for high-rise buildings, commercial offices, conference buildings, and so on.
- Steel truss. The truss structure is made of multiple rods that are hinged at each end of a rod. It requires less steel than regular steel structures, weighs less, and can withstand more force – which is why it’s often used for bridges, roofs, tower corridors, TV towers, oil platforms, and so on.
Design of steel structures
As with any moderately sized structure of any material, a lot of calculations have to be done at the design stage so that the building in question won’t collapse under its own weight. When it comes to steel structures, there are two main approaches to steel structure design (sometimes called a design philosophy):
- Load and Resistance Factor Design (LRFD, also called Limit State Design – LSD);
- Allowable Strength Design (ASD).
From the design standpoint, there are specific conditions that can be theoretically applied to steel structures called limit states. The limit state represents a point, after which a component or an entire steel structure is no longer capable of performing the purpose it was created for.
There are many different examples of limit states that can damage the structure in some way, making it unavailable for future usage – and this also needs to be kept in mind as early as the design phase, aside from the overall cosmetical approach to structure design.
Some examples of limit states are cracking, torsion, fatigue, shear, flexure, buckling, and so on. To tackle all of these potential issues at once, there’s a specific approach to steel structure design that has been implemented called LRFD – Load and Resistance Factor Design.
It is a method of structural engineering that uses limit states to analyze potential issues and create structures that would be far more likely to sustain those issues for far longer than before. This method accounts for both resistance and variability in load, achieving fairly high levels of safety for the majority of limit states.
If the concept of LRFD seems far too complex for you – there is an alternative called ASD – Allowable Stress Design. It is a relatively simple approach to building safety and mostly bases its calculations on a linear elastic behavior of the material in question – in our case it’s steel. It is mostly based on experience with the material and involves only two big factors – the potential maximum load of a structure and a linear safety factor.
When it comes to a direct comparison between ASD and LRFD when it comes to the design of steel structures, ASD would be the simple but less accurate one, while LRFD remains more complex, but also more reliable in its calculations. Additionally, LRFD takes into account way more factors when calculating its design, such as different values for live loads and dead loads – which are not calculated differently at all when it comes to ASD.
Levstal is capable of providing a lot of different types of steel structures, such as metal beams, cranes, bridges, quay constructions, shiploaders, ramps and even bearing structure elements. The company’s experience in working with steel is a guarantee of quality and variability.
Levstal’s services are used by clients from all over the world – from Germany, Sweden, and Belgium to Japan, North America, and the Netherlands, among others. Levstal offers support for the entire project’s lifecycle and personalizes the customer experience for each and every one of its clients.