Steel Frame construction

1. Basic System - Post & Beam (skeleton frame) and space frames.

2. Advantages of Steel Frame Construction:

1. Can build very tall and wide (tallest buildings in the world)
2. Light weight and strong (much lighter and stronger than concrete)
3. Prefabricated - frames assemble quickly
4. Precise and predictable (excellent quality control)

3. Disadvantages of Steel Frame Construction:

1. Steel is an expensive material (much more expensive than masonry or concrete)
2. Frames are unstable
3. Needs fire protection
4. Needs separate "skin" (walls and floors)

4. Methods of Stabilizing Steel Framed Buildings:

1. 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.
2. Diagonal Bracing - The addition of diagonal "X" or "K" bracing that resists lateral loads. Problems - may interfere with exterior windows.
3. 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.
4. 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.

5. Basic Structural Steel Shapes (Hot-rolled):

In general, structural steel is fabricated in a hot-rolled process under several ASTM designations, the most common being A36. This steel has a minimum yield stress of 36 KSI and a minimum ultimate (breaking) stress of 58 KSI. Many other grades are available, with A572 - 50 KSI yield stress as a choice for higher strength. A new steel grade A992 has recently replaced A572 and A36 (for W sections) as the standard grade. Like A572, it also has a yield stress of 50 KSI.

1. Wide Flange - The typical "I Beam" used in construction. Example - W18x35, where "W" = Wide flange, 18 = nominal depth of member in inches, and 35 = weight of beam in pounds per linear foot. Used for beams, columns, piles, bracing and other heavy applications.

1. Angles - Either equal legs or unequal legs. Example - L4x3x1/4 where 4 and 3 are the actual leg dimensions in inches and 1/4 = angle thickness in inches. Used for lintels, bracing, built-up beams and columns, secondary framing and other light-duty applications.

1. Steel Channels - These "C" shaped members are used for beams, built-up columns, bracing, secondary framing and other light to medium-duty applications. An example of a channel is C10x30 where "C" indicates channel, 10 is the actual height of the channel in inches, and 30 = pounds per linear foot.