Building Big

October 10, 2000

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1) The part of a structure that bears the weight or pressure of an arch. 2) A structure that supports the end of a bridge.
Arch: A curved structure that converts the downward compression force of its own weight, and of any weight pressing down on top of it, into a force along its curve. Thhis results in an outward and downward force along the sides and base of the arch.
Bending: Bending is caused by a combination of forces that cause one part of a material to be in compression and another part to be in tension.




A side support that counteracts an outward pusing force, the way bookends keep books on a shelf from sliding sideways. Buttresses are often used to support the sides of arches and walls of tall churches, where they counteract the outward thrust.
Compression: Compression is a pressing force that squeezes a material together.
Dome: A curved roof enclosing a circular space; a three-dimensional arch.



A push or pull on an object. When an object is at rest, any force acting on it is balanced by an equal force in the opposite direction.
Keystone: 1) Central wedge-shaped stone of an arch that locks the parts together 2) Central supporting element in a whole.
Loads create a force on a structure.
  • Dead load is the weight of the permanent, non-moveable parts of a structure.
    (In a room, the walls and carpeting, for example.)
  • Live load is the weight of a structures non-permanent, moveable parts, contents, or people. (Furniture, books, people in the room.)


Supporting structure 2) Central supporting element in a whole.
Span: Measure of space between two points. On a bridge, the span is the part over the rivero or canyon between supporting elements.


Tension is a stretching force that pulls on a material.
Torsion: Torsion is a twisting that can result from an unevenly placed load.
Truss: A skeleton-like structure composed of short straight pieces (struts), some in compression and some in tension, joined to form a series of triangles.
Shear: is a force that causes one part of a material to slide past another and usually causes a break or failure.
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