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Fig. 146 - Cutting up a beam |
to make an arch |
(visualization model) |
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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. |
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Fig. 147 - Roman aqueduct |
(scale visualization model) |
click image to enlarge |
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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. |
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I-beams |
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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. |
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a) Steel |
b) Reinforced concrete |
click image to enlarge |
Fig. 148 - Typical
I-beam
designs (demonstration
models) |
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Back to
Knowhere |
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Page 97 -
Building stability - Arched beam,
I-beam |
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