Benefits of Different Steel Sections | SkyCiv Engineering
Benefits of Different Steel Sections | SkyCiv Engineering
How often do we pay attention to the geometric shape of steel sections used in construction, and realize the importance of the shape? All the steel design and construction codes worldwide identify a few common shapes to be used as a steel member. These sections are noted by their cross-section shape profile. Below mentioned are a few commonly used sections.
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Why do we need different section types?
After going through the above list, one might wonder, why do we need to mold the steel sections into different shapes, instead use solid shapes (rectangular, square, circular or other polygons)? In order to know the reason, we need to understand a little about the load applications, structural phenomena subjected on member, parameters that control the structural capacity of a member.
Most common load applications that are encountered in the construction includes one or combination of below:
- Point Loads
- Uniformly distributed loads
- Moment/direct bending
- Rotation
Depending on type and manner of the load application/s, a member is subjected to one or combination of structural phenomena such as:
- Compression
- Tension
- Shear
- Flexure
- Torsion
In order to assess a member against the above-mentioned phenomena, there are few parameters (including but not limited to) that indicate the resistance offered such as:
- Cross section area
- Total Depth
- Thickness of Web, Flange/s, and Legs
- Moment of Inertia and/or Section modulus
- Torsional Constant
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Circling back to molding a solid section into different steel profiles; Based on multiple load combinations load applied, structural phenomena subjected and resistance parameter required, solid sections are molded and configured to various shape profiles. The molding of a solid section into shape profiles help to achieve high material to capacity ratio. Thus, conserving steel consumption (volume and weight).
Here we go through each section type briefly. We analyze each section type based on structural design criteria, usability and shape profile benefits.
I Shape / W Shape / H Shape
The shape profile of this section looks similar to alphabet “I” or “H”. W shape is the common notation used in AISC Steel Construction manual for this type of section. This section is used for all the types of load combinations, except pure rotation. This section is highly efficient to resist (in order) flexure, and compression. Most common usages of this section are beams/girder, columns in Buildings and Bridges.
Benefits
- High conservation of steel compared to solid rectangular or square section.
- Universal member - can be used for most structural member applications.
- Wide range of defined section availability in steel design manuals, allows for optimum structural design.
- Provides good compatibility for connections to other primary or secondary members.
Disadvantages
- Cannot be loaded in the X-X direction, as the section offer very little structural capacity compared to Y-Y direction.
- Offers less torsional resistance, since it is an open section.
C Shape / Channels
The shape profile of this section looks similar to alphabet “C”; hence we call them C shape. Channel is the common notation used in AISC Steel Construction manual for this type of section This section is mostly used for uniformly distributed load applications with small moment/bending. This section is highly efficient to be used as a secondary structural member where the loading is transferred onto other primary structural members. Most common usages of C Shape/Channels as secondary structural member are transverse joists supporting floor, purlins for roof trusses, studs in the wall framing, supporting members for ceiling assemblies, etc. Related: Try our purlin span calculator for C Sections.
Benefits
- Ideal substitute for I-shape when flexure is not a critical factor, conserving almost half the steel.
- Provides high structural capacity when used a multiple member system. Ex. Floor Joist system, Purlins in roof truss, etc.
- Can be placed back to back to create a virtual I-shape section.
- Provides good compatibility for connecting to other steel members and concrete/brick surfaces.
Disadvantages
- Highly unstable when loaded without bracing top flange, due to unsymmetrical geometry in Y-Y axis.
- Not suitable for heavy load applications.
L Shape / Angle
The shape profile of this section looks similar to alphabet “L”; hence we call them L Shape. This section is also called as “Angle” as noted in AISC Steel Construction Manual and also due to its feasibility to accommodate angular connections. This section is highly used for point load applications to resist shear, tension and compression. This section is a perfect fit to be used as a connection member, primary component of a built-up member etc. Most common usages of this section are connection between I-shapes and/or other shapes, bracing in truss members, Chords, Battens and/or Laces of built-up member, Diaphragm members in bridge girder system, Web stiffening elements for I-shape sections, etc.
Benefits
- Provides high structural capacity in connections to resist the bolt/weld shear.
- Highly preferred to be used as a bracing member for trusses, as they offer good combination of axial-flexural capacity (Tension/Compression).
- Can be placed back to back to create a virtual T-shape section.
Disadvantages
- Unsymmetrical geometry in both X-X and Y-Y directions.
- Very low material/structural capacity ratio offered, compared to other shape sections
T Shape / Structural Tees
The shape profile of this section looks similar to alphabet “T”; hence we call them T shape. Structural Tee is a common notation used in AISC Steel Construction Manual for this type of section. This section is usually split from standard I-shapes by removing the bottom flange. This section can be used for all load applications similar to I-shape section. This shape offers significant flexural capacity on the flange side compared to non-flange side. Most common usages of this section are connection member between I-shapes or other shapes, secondary beam members (lintels), Chord member in trusses and primary member of built-up member, End Diaphragm members in bridge girder system etc.
Benefits
- Ideal substitute for I-shape sections where one side flexure is not significant or to reduce the overall depth of member.
- Offers high axial - flexural capacity compared to L shape, due to web depth and symmetry.
Disadvantages
- Cannot be loaded in the X-X direction, as the section offer very little structural capacity compared to Y-Y direction.
- Very limited applications due to unsymmetrical geometry about X-X axis.
Square, Rectangular, and Round Hollow Structural Section (HSS)
The Hollow Structural section (HSS) is obtained by steel tubing in the shapes of Square, Rectangular and Round/Circular. This section is a closed class, compared to other sections discussed above. This section is highly applicable for point loads and rotation. This section provides high structural capacity against compression and torsion. Most common usages of this section are structural column, shafts, etc.
Benefits
- Provides high torsional resistance compared to I, C, L, and T shapes.
- Provides high structural capacity in both directions (X-X and Y-Y) compared to I, C, L, and T shapes.
- Can be used as a jacket for concrete column for increased axial capacity.
- Relatively beneficial weight:capacity ratio (in axial)
Disadvantages
- Not commonly used as flexural member due to more steel usage compared to an equivalent I-shape section.
- Connections such as bolting is hard to install, since the section is closed.
Conclusion
Other shape sections that are also used as steel member are Pipe section, Plate section, and Bar sections. Based on above discussion we can now understand the differences between different shape sections, their relative benefits, their structural strengths etc. An optimum structural design includes all the above individual shape sections to be correctly chosen, designed to support and transmit loads properly throughout the structure.
6 Qualities For Steel That Will Last A Lifetime
Steel windows and doors are a significant investment for the custom home that come with two big expectations: performance and longevity. Unfortunately, this is not always the case. Low-quality steel products carry a higher risk of rust, warping, leakage, and difficult repairs. And getting a product that is high quality is not always easy – many low-quality products are difficult to differentiate in photos, and are often marketed as a high-quality product than they really are.
That’s why knowing which factors actually increase longevity is critical when choosing a steel window and door manufacturer. Knowing the difference will help you procure a product that will last a lifetime and not one that will quickly lose attractiveness, function, and value.
1. Quality Profiles Matter
Knowing the source of the profiles used to be build your steel windows and doors is the most critical factor to ensuring that you have a high-quality, long-lasting product. There are two main types of steel profiles: manufactured and shop-built.
Shop-built profiles are produced by hobbyists or local welding shops who weld separate components together to create a single unit. While some local shops do a better job than others, shop-built profiles tend to be of more inconsistent (and usually inferior) quality. These profiles are prone to issues, such as rust, warping, and buckling, which can cause severe problems, such as leaking or becoming inoperable over a short period of time.
Montanstahl Steel Profiles
On the other hand, manufactured profiles offer consistent, high quality units time after time. Manufactured units are made from one solid piece of steel, which provides greater strength and durability. Some of the big names in this space include Montanstahl, Jansen (both Swiss) and Secco Sistemi (Italian). All use Mild Carbon Steel (S235JR which is equivalent to A36) to produce their profiles, which are either hot rolled or cold formed depending on application.
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Having a quality profile provides the best foundation for creating a long-lasting steel unit.
2. Rust Prevention > Repair
Rust is the #1 enemy of steel, and it is guaranteed to occur if bare metal becomes exposed to oxygen and moisture. Rust can happen quickly if proper preventative measures aren’t taken. On exterior units, it can happen in as little as 4-14 days; on interior units, it can take a little longer, depending on the humidity of the area, but will still appear within 3-6 months.
That’s why, after a good profile source, the most critical component of quality steel windows and doors is rust prevention. But note, not all rust prevention methods have equal outcomes, and the one you choose will have a direct impact on the longevity and maintenance of your units. The most common types of rust prevention on a steel unit are zinc primer and galvanization.
A zinc-based primer can provide adequate rust protection as long as it’s intact. However, because it doesn’t have a strong bond to the underlying metal (typically 300-600 psi), it can be easily damaged through normal wear and tear, leaving the steel itself exposed to air, and therefore rust. In general a unit coated with a zinc-based primer will last about 12-15 years before it needs a major repair – much less than the “lasts a lifetime” feeling you want for you steel windows and doors.
Galvanization, therefore, is a much better form of rust prevention. Galvanization has a high bond strength (3,600 psi) and provides excellent corrosion protection and abrasion resistance. Hot-dipped galvanized (G90) steel windows and doors will typically last 75+ years until the rust prevention needs its first major repair.
3. Finish Type + Ease of Ownership
Along with profile source and rust prevention, finish type completes the “trifecta” of the most critical quality elements. Finish type is both aesthetic and functional. It affects how the finished product looks, but also provides an important surface barrier against normal wear and tear. It also is a major contributor to ease of ownership – like any part of your home, steel windows and doors require some upkeep, and the finish type often determines how easily typical maintenance can be performed. Three of the most common finish types are standard paint, powder coat, and cured paint.
Standard paint, while able to be touched-up onsite, is not very durable on steel units, which means moderate maintenance will be required. Couple that with visible brush strokes, and standard paint is overall not a great long-term choice.
Powder coating a unit provides more durability than standard paint, but at a high maintenance cost. Unlike other finish types, repairs to powder coated units are impossible to complete onsite. Units must be shipped to a facility and sandblasted, then recoated. The shipping and repair costs are usually covered by the home owner because normal wear and tear is not covered by a warranty.
The best type of finish you can have for your steel windows and doors is cured paint. This finish type provides a sleek, smooth surface texture that is both attractive and durable. Inevitable wear and tear can be repaired onsite by a homeowner or handyman, as it only requires touch up paint.
4. Energy Efficiency
Energy efficiency is becoming more and more important in local codes, which means choosing a steel unit that can meet local code is important. Most steel window and door companies do not have test results from the National Fenestration Rating Council, though some high-end companies will have stickers showing NFRC data.
The type of glass selected for exterior units has a considerable impact on the overall energy efficiency of the structure. Double and triple pane glass combined with Argon gas effectively prevents heat transfer. There are various insulation levels available to suit the needs of any climate.
Another option that plays a big role in energy efficiency is thermal breaks. Thermally broken profiles use resin isolators inside the steel profile to reduce heat transfer in harsh climates. These profiles are particularly important in colder climates – the thermal break stops the metal frames from getting cold on the inside of the house, which prevents interior humidity from condensing on the metal frames.
Thermal breaks are a complicated factor of steel windows and doors, and there are many factors that determine whether it is the right choice for your house. For a deeper dive into thermally broken steel windows and doors, click here.
5. Glazing Methods
Glazing refers to glass installation and the method that holds the glass in place. As the primary defense against the elements, high-quality glazing creates an airtight and watertight seal. It is also a major contributor to the style of the unit. There are three methods of glazing: wet, dry, and putty.
Both wet and dry glazing methods utilize a T-bar and a glazing bead (which gives the muntin its attractive shape). The primary difference between the two methods is how the glass adheres to the frame. With dry glazing, this is accomplished using a rubber gasket, while wet glazing utilizes either a caulk or adhesive. With either glazing method, glass can be removed and replaced with relative ease.
Putty glazing uses a malleable putty to hold the glass in place. This is a very traditional glazing method, but putty glazed units are relatively difficult to replace as few glass companies use this method.
6. Hot Rolled vs. Cold Rolled
Steel for fenestration is formed one of two ways: it is either hot rolled or cool rolled. Hot-rolled steel is heated to 1,700°F, extruded to produce the profile shape, then cooled. This method produces profiles with a classic steel appearance. Cold-formed steel is heated to °F, cooled, then rolled into sheets and mechanically formed into the profile shape. This method produces very precise shapes ideal for thermally broken profiles.
Neither type of steel is inherently better than the other. While both have strengths and weaknesses relative to the other, and are suited to different applications. A reputable manufacturer will not vilify one process versus the other.
Summary
High-quality steel doors and windows can be a stunning addition to your home, but sorting through the many manufacturers and different quality levels on the market is often difficult. The points discussed in this article can help you make an informed decision when considering steel for your project. Knowing what to look for and asking the right questions will help ensure that the products used in your home are going to look great and operate well for years to come.