Structural Steel Properties, Types, Beams, Connections and Glazing

Steel: Properties and Characteristics

Steel: One pound of steel has more strength than one pound of most other materials. Steel is generally equally strong in tension and compression. There are many ways to use it: columns can be spaced at great distances, and long spans are possible. Steel corrodes if not protected and loses strength when exposed to fire. Steel contains iron.

Types of Steel

• Carbon Steels: 0.15–1.8% carbon (includes spring steels).
• Alloy Steels: Contain additional ingredients such as chromium; stainless steel typically contains about 12% chromium and is more rust resistant.

Tips: Higher carbon content increases hardness and can make steels more difficult to weld.

Shapes and Sections

Shapes:

• W = wide-flange
• C = channel
• S = I-section (American standard)
• L = angle
• Pipe or tubing
• Bars, plates
• WT or T sections

Corrosion and Galvanic Action

Corrosion: General corrosion and galvanic corrosion occur due to electrochemical action between more noble and less noble metals. Protection or coatings are required to prevent rust.

Fire Resistance and Protection

Fire: Fire-resistive protection or coatings are required because steel can lose strength in fire. Materials often used for protection include gypsum, cement, water-based systems, and other fireproofing materials. Different thicknesses and types of fireproofing affect performance; larger or thicker protection tends to provide longer resistance.

Beams and Girders

Beams or Girders: Used for framing as single beams or multi-layer systems.

Box Girders and Castellated Beams

Box Girders: Built up from shapes, box girders resist lateral loads and often have a hollow section.

Castellated Beams: Have a deeper section, allow longer spans and higher load capacity, and can provide useful space inside the web openings.

Connections and Fastening

Connections:

• Bolted: Allow the member to be replaced if necessary.
• Welded: Require additional detailing and rigidity.
• Riveting: an older method of fastening (historically replaceable).

Open Web Steel Joists

Open web steel joists: Look like trusses, provide increased depth, can span long distances, and are relatively easy to install.

Framing and Bracing

Framing: Includes horizontal and diagonal bridging (bracing) to stabilize members and distribute loads.

Steel Columns

Steel columns: Can be wide-flange (W), round pipe, rectangular tube, welded plate sections, two angles back-to-back, cruciform, or built-up from four angles. Columns can be combined with other materials when required.

Curtain Walls

Curtain wall: An exterior wall system supported by the building's structural frame (steel or concrete). A curtain wall typically supports its own weight and resists lateral loads (wind), transferring those loads to the structure. There is a gap between the primary structure and the curtain wall; the curtain wall is often a hanging, non-loadbearing envelope that can move independently of the structure.

Roof Framing and Purlins

Roof framing: Roofs can be flat or sloped to various degrees. Steel rigid frames can be large welded components; they are strong and may require fewer joists. Frames are commonly made for clear heights such as 20'–24' and 30' tall, with bolted connections.

Girts are horizontal members where walls or sheathing (plywood or curtain wall systems) are attached. Purlins are roof members spaced typically about 4' to 5' and support roof sheeting or decking; purlins can be designed with one or two layers depending on the roof system.

Space Frames

Space frame: A three-dimensional, lightweight structure that provides large spans and high strength. Cons: can take a lot of space. Space frames can be bolted, pinned, or welded and in many cases can be disassembled.

Steel Stairs

Steel stairs: Often use steel pan treads filled with 2" concrete as formwork; treads can also be open.

Glass and Glazing Materials

Glass: Made from sand that is cooked; silica is the basic raw material, with additions such as sodium (soda) and calcium.

Types of Glass

• Float glass: Conventional, thinner and transparent; can be dangerous when broken.
• Tempered (tempered) glass: Starts as float glass but is heat-treated or stretched; breaks into pebble-sized particles and cannot be modified (cut or drilled) after tempering.
• Laminated glass: Two layers of glass with a plastic interlayer; used for impact windows, sound control, and energy conservation.

Glazing Frame Materials

Materials: Common framing and window materials include aluminum, wood, vinyl, and fiberglass.