2.3 Internal Forces within
Structures
Internal force


Force that one part of a structure exerts on another part
of the same structure
Example

Press your hands together
Compression

Force that squeezes an object
Tension

Force that acts to stretch and pull apart something
Shear

Force that acts to push parts of a structure in opposite
directions

http://www.pbs.org/wgbh/buildingbig/lab/forces.html
Complementary Forces

When different kinds of internal forces act on a structure
at the same time

See Figure 2.26 page 298
2.4 Designing structures to resist
forces and maintain Stability
Seven wonders of the world
What shapes do
you think helped
these structures
withstand the
forces on them?
What materials
last the longest?
Shapes

Triangle the strongest structural shape
Structural components

Arches

Can support a large load because it spreads out the load
Beams



Flat structure that is supported at each end
I-beams
Girders (box beams)
Truss

Framework of beams joined together
Cantilever

Beam supported only at one end.
Columns

Solid structure that can stand by itself
Notes (columns, crossbeams)
(arches, columns, crossbeams, triangles,
truss bridge)
(arches, arch bridge, columns,
crossbeams)
(columns, crossbeams, arches, truss’)
Structural Stress: weakening of a structure
due to internal and external forces

Structural fatigue

Permanent change in a
structures caused by
internal forces

cracks

Structural failure

Collapse of a structure due
to the forces




Materials
http://www.pbs.org/wgbh/
buildingbig/lab/materials.ht
ml
Shapes
http://www.pbs.org/wgbh/
buildingbig/lab/shapes.html