It's easier to conceptualize castellated beams when you consider the word "castellated," which references the notches or battlements in castle towers. Castellated beams are I-beams or girders with notches cut from the center member. The notches -- whether they are square as in a castle or octagonal or any other shape -- reduce the weight of the beam without greatly reducing its strength. The result is a beam with a higher strength-to-weight ratio.
Castellated Beams and Tensile Strength
Castellated beams are able to deliver higher strength-to-weight ratios because of the dynamic of tensile strength in their webs. The openings from the holes leave an X shape intact between the top cord and bottom cord. For the beam to fail when a load or force is exerted, it does not just have to bend or collapse, it has to stretch the cross-members of the Xs. The strength to withstand pulling or stretching force is called tensile strength. Steel, while it is bendable, has extremely high tensile strength. So, castellated beams are configured to use steel's (or other metals) high tensile strength.
Welded Castellated Beams
Before the popularity of computer numerical control or CNC machines and advanced metal-cutting systems such as laser cutting, it was more efficient to manufacture castellated beams in two sections. The I in the I-beam was bisected. That allowed for older mechanized ways of cutting the castellations in the beams. It could be done with anything from a large saw blade or cutting wheel to a cutting torch. Once the castellations were cut, the top and bottom half would be welded together.
Lazer or Plasma-Cut Castellated Beams
Today, castellated beams use advanced cutting systems in conjunction with CNC-controlled cutting heads. Systems include hydro-jet, laser and plasma cutting. A CNC machine is attached to a device like a plotter, which can quickly move the cutting head in any shape.
Drilled Castellated Beams
Castellated beams are sometimes drilled, particularly if they're smaller. Frequently, a drilled castellated structural member is used in different types of fabrication such as aircraft. A wide variety of machines use the benefits of the castellated beams' strength-to-weight ratio on a smaller scale. The metal used is more likely to be aluminum if a small-scale castellated beam or structural member is used.
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