Steel frame construction, in which a skeleton framework of structural steel supports the walls, floors, and roofs, is commonly used today in commercial and industrial buildings not only in small one or two story office buildings and shopping malls.
The steel component known as the structural “C” is the predominant shape for framing floors, walls, and roofs. The primary difference from one use to another is the thickness of the steel and the depth of the member.
All steel structures must be fire protected as per state and local building codes. Although it takes a very substantial amount of heat to actually melt steel, it will lose most of its strength at temperatures above 7000 F. There are generally two major categories of fire proofing – thermal and absorptive.
1. Thermal Fire Protection – Slows heat passage through the steel. Methods used include providing insulation and intumescent paint.
2. Absorptive Fire Protection – Absorbs heat. Methods used include covering steel members with concrete, gypsum (spray-on), and elaborate methods such as liquid-filled chambers (generally wrapped around columns).
Advantage of Steel frame construction
- Consistent Material Quality
- Light weight and strong
- Non-Combustible Material
- Dimensionally Stable in any Climate
- Insect Resistance and steel will not Rot
- Can build very tall and wide (tallest buildings in the world)
- Prefabricated – frames assemble quickly
- Precise and predictable (excellent quality control)
Disadvantages of Steel Frame Construction:
- Steel is an expensive material (much more expensive than masonry or concrete)
- Frames are unstable
- Needs fire protection
- Needs separate “skin”
Methods of Stabilizing Steel Framed Buildings:
Rigid Core – Usually accomplished by interior masonry (or concrete) stair towers and elevator shafts that creates a vertical rigid core that resists deformation and torsion of the building due to external lateral forces.
Diagonal Bracing – The addition of diagonal “X” or “K” bracing that resists lateral loads. Problems – may interfere with exterior windows.
Moment-Resisting Beam-to-Column Connections – Typically accomplished by fabricating extra connection angles, welds and bolts that greatly increase the rigidity of the connection. Problems – extremely labor intensive and expensive.
Shear Walls – Exterior (or interior) walls built of masonry or concrete that act as a vertical cantilever beam resisting lateral loads. Problems – may interfere with exterior windows, labor intensive, heavy.