Whether it’s a municipal infrastructure project, a multi-story building, or a small scale model (as shown above), steel framing typically includes many welded joints. As a welder, you’re bound to work with framing components at some point, either in the shop or out in the field. If you’re infamiliar with the principles and terminology of construction, this page introduces the basics:
A truss is a framework used to construct bridges, buildings and airplanes. There are lots of different types, but in general it consists of a top chord, bottom chord and diagonal web. The bridge in the photo above has a truss on either side. As you can see, the diagonal members provide bracing in a triangular arrangement. A truss resists the forces of compression (pushing in) and tension (pulling apart).
Two types of structural elements, struts and ties, are associated with bracing in trusses. Struts are inserted to resist compression. Ties resist tension. (Ties are sometimes referred to as connectors.) When engineered correctly, a truss is considered an ideal means to handle loads over a long period of time without yielding, deforming or breaking. In the case of bridges, trusses may also span large distances because they can be built or prefabricated in sections.
Watch an animated guide to see how compression and tension work.
A construction beam has many names, such as I-beam, H-beam, girder, rolled steel joist , or “RSJ” . It’s defined as a horizontal structural member that supports vertical loads. The long central component of a beam is called the web. The two short ends are called flanges. This particular shape was designed to maximize the steel’s load-bearing capabilities without the builder having to use heavy solid blocks of metal. Even though the flanges appear easily bendable, and the web too scrawny to hold much weight, compression tests show the design works well.
A gusset plate connects two or more structural members along one plane, as shown above. Bridge trusses commonly use gusset plates for multiple intersecting components. The plates are designed to minimize bending at the connections, which enables the members to do their job resisting tension or compression. The dots you see on this plate are rivets.
Joists are a series of long constructions that support a roof or a floor. The triangular bracing inside two beams takes advantage of the same principles as a truss, so the two types of structural components may be sometimes confused. Just remember, a joist holds up a deck, roof or floor, and there are lots of them spread across a horizontal plane, as shown above. Each joist provides rigidity and exceptional load-bearing properties, and together they keep the decking or roof from collapsing inward or breaking at any one point. Moreover, The forces of tension and compression are distributed evenly across the entire expanse – a key objective in structural design.
These are secondary, horizontal members laid out to hold the sheeting that will be laid out on the roof. In th diagram above, note the outermost member, which is called an eave strut.
Purlins are made of lighter-gauge steel than girders, since they’re not used to hold up heavy loads. They may be galvanized to better resist corrosion, especially from water damage. However, they’re not particularly resilient in the face of strong winds. This is why commercial buildings often sustain costly damage during tornadoes and hurricanes.
In architectural terminology, an eave is the line or intersection of the roof and wall panels. Hence, eave struts are long, thin-walled members installed at this location to support roof and wall panels.
Sheeting rails, also known as girts, are typically light-gauge steel members used to hold wall cladding in place on buildings. Like purlins, hey’re not meant to support the load of the building itself. As you can see above, the red I-beam is the main structural member.
Decking is a flat surface that sits atop the floor and roof joists in a building or other structure. Multiple sheets of metal, usually corrugated, interlock and are fastened or welded together. In the photo below left, a welder is welding together segments of the decking.
A pier is typically a concrete structure designed to transfer a vertical load from the base of a column to a footing. As you can see on the far right side of the photo above, the concrete is poured around a sturdy steel box frame. In an earthquake, even if the concrete starts to crumble, the steel frame should still hold the freeway or other horizontal structure in place.
A pile is a long column driven deep into the ground to form part of a foundation or substructure. Piles can be made of steel, concrete or wood. The steel type may take the form of pipe or beam, such as the popular H-pile in the photo above right.
Reading Diagrams and Schematics
It takes practice for a new welder to interpret blueprints, schematics, and shop drawings, but the sooner you get comfortable with these documents, the better. One way to ease the learning curve is to start with 3-D architectural views and simple structural diagrams. From there, you can move on to more complicated line drawings and specs. Here are some examples and a video tutorial:
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2010 Specification for Structural Steel Buildings (ANSI/AISC 360-10) American Institute of Steel Construction
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