Prefabrication experiments - 364 - Modern structural archetypes - 04 - Castellated Beams

Beams and arches are archetypes of horizontal spanning structures. In particular, beams make it possible to span horizontal distances without the geometric and vertical constraints of arched, domed or vaulted shapes. Beams resist vertical loads by their in-built strength and distortion through physical inertia linked to their material properties, their sections and dimensions. Henry Grey’s wide flange beam revolutionized construction as its iconic «I or H» shapes were rolled and normalised to varying heights, widths and thicknesses. Further, for the first time in the history of construction, the beams employed a material, steel, that was equally resistant in tension and compression making them formidable tools to construct vertical buildings. Even with its great density, steel can be shaped to reduce material use.

 

Understanding beam effect under bending, compressive forces in the top flange, tensile forces in the bottom flange and a neutral axis in the center of the beam, informed the canonical beam shape. Inertia, a function of the vertical distance between both flanges, and a robust axial web resist torsion. This simple principle of all bending structures applies to wood, steel, concrete beams, slabs and space frames. Any horizontal spanning structure can be analysed and optimized through this beam effect.

 

Grey's beam invention remains largely utilized in construction and many have sought to further optimize its beam effect; The Castellated beam invented in 1926 by Fredellia H. Moyer studied a type of optimisation that expands on the reaction forces in bending structures. By eliminating material close to the beams' neutral axis, without affecting inertia and compressive or tensile constraints, the beam can me made lighter and therefore span longer distances as it flexes less under its own dead weight. The production process of a castellated beam illustrates these principles by symmetrically cutting a standard beam longitudinally through its web in order to form a half/hexagonal zigzag pattern. When the beam halves are matched to reveal the hexagons and then soldered they create a much lighter continuous structural element. 

 

The hexagonal openings can create an open network for wiring or ducting making floor thickness far more flexible than with solid beams. Castellated beams have been and are still used in architecture and construction to illustrate the possibilities of augmenting a component’s span to weight ratio simply by reformatting it in relation to beam effect. Openings in beams can also be circular or rectangular and are a function of maintaining the web's shear and torsion resistance.

Castellated beam pattern