Columns: Using up to
5 sheets of paper, make a structure that will support a load( clay bricks)
8-1/2" off the table.
Minumum Load:12 batteries or 2 bricksDiscussion: Limitations
of post-and-lintel construction: Why do Greek temples need all
over (rotational motion)
(2) Long(slender) columns-
fails at one point, then collapses
Euler Buckling: Critical load depends on length, stiffness, and cross-section of column.
Thus for a given amount of material, a hollow column is less subject to buckling, as it has a greater cross-sectional area.
fails at end- what happens if ends are reinforced, as in paper cups?
(3) Material Failure( Crushing)- Short Columns
Very short columns crush
Most columns are intermediate- fail partly in crushing and partly in buckling.
crushing strength of 1 paper cup( in bricks)
paper cups will support a student?
are typically paired with horizontal beams to provide the structural
framework for most buildings today. Columns become strong under compression,
the squeezing produced by the downward force exerted by a load and
the counteracting force upward from the ground. A column must manage
two types of load: (1) the dead load, or weight of the structure it
supports plus any permanent fixtures, and (2) the live load, which
includes people, furniture, cars, or other temporary objects whose
weight bears down on the structure.
designed and loaded, a column (or grouping of columns) is able to
support a lot of weight because it transfers it directly to the ground.
A column can fail in two basic ways. A load placed off center subjects
the column to bending, or buckling. To prevent this, it is important
to center a load squarely over the middle third of the top of the
column. The second kind of failure occurs when the maximum strength
of a column's material is exceeded by the weight of the load. When
this happens, the column crushes, or collapses.
Even hollow, thin-walled
columns made of weaker material can be made strong under the weight
of a heavy load. A paper cup with its bottom removed, for example,
is no match for the weight of a person standing on it. It crushes
easily because the paper is weak in compression. Filled with sand,
however, the paper cup can withstand the same weight -- and then some.
Why is this so? Paper is fairly strong by itself in tension. It resists
the sand's outward thrust, preventing it from spreading out. Thus
contained, the sand in turn prevents the paper from collapsing by
resisting the downward force of the weight and making the column stronger
in compression. Engineers can sometimes use an inexpensive filler
material that is strong in compression -- like sand or loose rocks
-- to reinforce a hollow, thin-walled column, allowing them to build
safely and cost-effectively.