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Forces Lab |
Materials Lab |
Loads Lab |
Shapes Lab
These labs simplify the real-life conditions that affect structures (shapes), in order to illustrate key concepts. In the real world, many variables affect the strength and stability of any give shape. The choice of materials, joints, load distribution, and size and thickness of a structure all affect its ability to resist loads. For example, a triangle made of paper would collapse much sooner than an arch made of steel -- an effect that was not demonstrated in this lab.
The shape comparisons in this lab depend upon the following conditions: each shape is of equivalent thickness, the joints are hinged, and the live load is applied downward to the structure at a single point at its top and center.
The shape of a structure affects how strong it is. Rectangles, arches, and triangles are the most common shapes used to build big structures.
The weight pushes down on the rectangle and causes the top side to bend.
The weight presses down on the arch and is spread outward along the curve to
the ground below.
The weight causes the top two sides to squeeze together and the bottom side to pull apart.
The weight caused the top side to bend too much, so it failed!
The arch likes to be pushed and squeezed. The weight pushes this arch into a
stable, tightly squeezed shape.
Unlike the rectangle, the sides of the triangle did not bend under the tremendous weight. This is why the triangle is still standing.
The weight caused the top side to bend too much, so it failed!
The arch likes to be pushed and squeezed, but not this much! When an arch is pushed too hard, the sides spread apart and collapse.
The triangle is still standing because the pulling force in the bottom side is balancing the pushing forces in the upper sides.
The weight caused the top side to bend too much, so it failed!
The arch likes to be pushed and squeezed, but not this much! When an arch is pushed too hard, the sides spread apart and collapse.
Even triangles have their limits! All this weight made the third side stretch so much that it snapped in half.
What happens when you push the side of a rectangle?
The rectangle is a wobbly, unstable shape. When you push the side, it flops into a slanted parallelogram. This happens without any of the rectangle's sides changing length.
Now when you push the side, the diagonal brace gets squeezed, preventing the rectangle from flopping over.
What happens when you push down on an arch that is not supported on both sides?
The force of the finger pushes the sides of the arch outward.
As the arch tries to spread outward, external supports, called buttresses,
push back on the sides of the arch and prevent it from spreading apart.
What happens when you push the side of a triangle?
The outer edge squeezes together, and the inner edge pulls apart. When one side experiences these two forces at the same time, it bends. The weakest part of the triangle is its side!
When you poke the top of the triangle, the two sides squeeze together and the bottom side pulls apart. The triangle doesn't bend because each side experiences only one force at a time. When used properly, triangles are the most stable and rigid shapes used in construction today.
Flash version of this lab
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