3 Crucial Design Considerations When Constructing With Cold-Rolled Steel

If you are looking to build your own property, or even build a new roof or extension, it is important to understand the performance of different construction materials. Cold-rolled steel is commonly used in building construction due to its strength and stability; however, there are a few key design aspects you must consider before designing your new property: 

Buckling Performance

As with any structural material, buckling is one of the most important design considerations when constructing cold-rolled steel. Buckling occurs due to instability of a member and occurs before the material reaches yield point. Due to the structural instability introduced by buckling, it is important to understand the different mechanisms that can lead to structural collapse. With cold-rolled steel, there are three main modes of buckling: 

  • Euler buckling - Often referred to as classic or global buckling, Euler buckling occurs when the compressive load on the structure exceeds the maximum buckling resistance of the member. 
  • Distortional buckling - This buckling mode is induced by excessive distortion of the element cross-section and is typically caused by the collapse of a section's flange-lip junction. 
  • Lateral-torsional buckling - "LT" buckling can only occur in an unrestrained beam, and the mode is induced due to the member bending out-of-plane. This torsion causes a twist in the material that weakens the section, making it more susceptible to collapse. 

The buckling performance of cold-rolled steel is different to that of hot-rolled steel due to the different methods of manufacture. For hot-rolled steel, the design emphasis is on the strength of the material which is increased during the manufacturing process. For cold-rolled steel, however, the performance is governed mainly by the shape of the cross-section as the material is not heated prior to molding. 

Fire Resistance

The performance of steel under intense heats is paramount as the material quickly tends towards yield at elevated operating temperatures. Steel buildings that are exposed to internal fires do not perform as well as concrete structures. Therefore, it is important to consider the effect of high temperatures on an internal steel support structure. 

Due to cold-rolled steel not being heated prior to molding, the material loses more strength at high temperatures than does hot-rolled steel. However, the performance of this material can be increased by a couple of novel methods. 

Specifically, the fire resistance of cold-rolled steel can be increased significantly by using sprayed protective coatings or plasterboard linings. Both of these methods increase the fire resistance of cold-rolled structures by acting as "buffers" that resist fire long enough for the steel to remain unaffected. Both of these methods can give steel designers some peace-of-mind when designing for a particular fire resistance level. 

Flexural (Bending) Performance

Steel is widely used for the construction of beam elements due to their high performance under bending. Particularly for long beams that are exposed to significant loads, steel has shown itself to be the most resistant of all common construction materials. Where concrete has been used, steel is commonly inserted into the concrete in order to reinforce the material prior to application. 

Both hot-rolled and cold-rolled steel perform the same under bending; there is no difference in performance because of the difference in manufacturing. With that said, not all sections are the same; rather, there are some critical factors to consider when designing a steel beam: 

  • Geometry - The geometry of the cross-section is one of the most important factors in determining the performance of a steel beam under bending. This is because different sections have different moments of inertia, which govern a member's resistance to bending. Typically, the deeper a section is in relation to its width, the better it will perform under bending. 
  • Grade - The grade of a steel describes the quality of the material, which is important in determining the bending behavior of a beam. For structural steel, grades are denoted by the letter "S" and are categorized according to their yield strength. The higher this value is, the better it will perform under bending. 
  • Length - Long beams will deflect more under load than short beams. As such, it is important to predict this bending prior to loading the beam in order to determine optimal positions for vertical supports. 

For more information about cold rolled steel, check out a company like A & C Metals - Sawing.