Polymorf - Knowhere - Arched beam, I-beam

of the beam must span. And it shifts the internal stresses to compression mainly, which

stone is especially capable of resisting due the nature of its atomic structure. The arch

design facilitates this by enabling the vertical loads to be collected and displaced laterally

around the curved mass of the arch so that they are concentrated at the base. There the

legs of the arch must be prevented from spreading apart from the thrust of the weight by

the abutments against which they rest. For the most efficient displacement of the load the

rise of the curved section of the arch should be equal to about one-half of its span. Many

examples of arched Roman aqueducts survive to this day attesting to the extraordinary

stability of the arch design.

Both the post and lintel, and arch designs rely on the mass of the structural members to

resist the stresses of their loads. To repeat, this is a very inefficient use of material which

contributes substantially to the dead weight of the structure itself. Modern designs optimize

the shape and arrangement of members to build more efficient structures.

I-beams

As with columns, increasing the moment of inertia of a beam to increase its stiffness can be

achieved by placing as much of the beam's material at the outer edges of the beam's cross-

section, and eliminating as much material from the center, as is practical. A modern beam

(or column) design that permits this is the I-beam, so named for its cross sectional shape.


a) Steel		b) Reinforced concrete
click image to enlarge
Fig. 148 - Typical I-beam designs (demonstration models)

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