Frequently Asked Questions

We asked our resident steel expert and certified engineer, Nader R. Elhajj to give us the low down on some of the frequently asked questions.

1. What are the applications of cold-formed steel (CFS)?

Cold Formed Steel shapes can be used for roof systems, floor systems, wall systems, roof panels, decks, or the entire buildings. They can also be used as individual framing members such as studs, joists, headers, and truss members. Cold Formed Steel members can also serve as both primary structures and secondary structures. An example of the Cold Formed Steel used as primary structures is the FRAMECAD webbed trusses. Steel studs can also act as secondary structures by providing lateral support to exterior wall finish since they rely on the primary structure for support.

2. What is the difference between hot-rolled steel and cold-formed steel?

There are many differences between the two materials:

• Cold-formed steel (CFS) is typically limited to light thicknesses (up to 3.00 mm) while hot rolled steel can be manufactured to any desired thickness.
• CFS shapes are different than hot rolled shapes and endless geometrical shapes can be produced.
• CFS is manufactured at room temperature while hot rolled steel is made at elevated temperatures.
• CFS lightweight makes it easier and more economical to mass-produce, transport and install.
• In the design of hot-rolled steel shapes, the primarily concern is column buckling and lateral buckling of unbraced beams. The dimensions of hot-rolled shapes are such that local buckling of individual elements generally will not occur before yielding. In the case of CFS local buckling must also be considered because, in most cases, the material used is thin relative to its width. This means that the individual flat, or plate, elements of the section often have width to thickness ratios that will permit buckling at stresses well below the yield point.

There are many codes and specifications that govern the design of cold-formed steel structures around the world. Each country has its own specification or relies on one of the internationally recognized specifications. The most widely used ones are:

• AISI S100 North American Specification for the Design of Cold Formed Steel Structural Members published by the American Iron and Steel Institute (AISI) in the United States.
• AS/NZS 4600 Australian/New Zealand Standard-Cold-formed steel structures jointly published by Standards Australia and Standards New Zealand.
• BS 5950-5 Structural use of steelwork in building-Part 5. Code of practice for design of cold formed thin gauge sections published by BSI in the UK.
• Eurocode 3: Design of steel structures; Part 1.3: General rules, Supplementary rules for cold-formed thin gauge members.

4. How many storeys can a cold-formed steel framed building go up to?

Several 8-storey buildings have been constructed in the USA and Europe using cold-formed steel framing. The first 8-storey building in the USA built with steel framing was completed in 1999 in Seattle, Washington (a high seismic area).

Mid-rise buildings (5 or 6 levels) in cold-formed steel are also very common and many have been built around the world in the past 20 years or so.

From an engineering point of view, there is no limit on the number of storeys that can be built with cold-formed steel framing.

5. What is the maximum span for steel truss?

One of the biggest advantages of cold-formed steel is its high strength to weight ratio. This allows manufacturers and framers to fabricate long trusses with clear spans up to 25 meters.

Steel trusses can be easily designed with clear spans up to 14 meters. Beyond that, a thicker material or boxed profile would be required along with specially designed connections. (Note: In many areas, there are transportation limitations when truss span exceeds 15 meters). For long trusses, intermediate bearing supports can also be used to reduce the size and thickness of the truss members.

6. Are the same foundations and footings that are used when building in concrete suitable for construction with cold-formed steel?

Cold-formed steel is much lighter than concrete. It weighs approximately 5 psf (0.24 kPa) while concrete ranges from 30 to 70 psf (1.45 to 3.35 kPa). In most cases, using cold-formed steel means the amount of concrete used in the foundations can be reduced. Your structural or foundation engineer should be made aware of the loads acting on the concrete so that the foundations can be designed accordingly.