STRUCTURAL STRENGTH
AND STABILITY

When an object is stable it is well
balanced and will not fall over unless
force is applied to make it topple
over. It has a strong center of
gravity.

Example: The Eiffel tower,
this ballerina, my lamp

When an object is unstable it is
not well balanced and may fall
over.It does not have a good
centre of gravity.

Example: This person, a
3/4 legged chair

Structures, objects and even
people and animals are all made up
of mass. This mass is acted on by
gravity. In every object there is a
point where all mass is concentrated,
this is called the Centre of Gravity.

Example: My bellybutton,
centre of a book

The bases of support support the
Centre of Gravity by supporting
the mass. It is the base that
helps the structure remain stable.

Example: My legs, chair legs,
the legs of this giraffe

Static Loads

A Static load is the force
of gravity pulling the load
down to the core of the earth.
So gravity creates a downward
force on the structure which
pulls the structure towards the
core of the earth. There are two
types of static loads. Dead Loads
and Live Loads.

A Dead Load is the force
of gravity acting on the
structure itself.

A Live Load is the force
of gravity acting on objects
that are not permanently
attached to the structure or
dead load.

Dynamic Loads

A dynamic load is a force that
is other than gravity. These
forces can in fact act on
structures and change how
stable they are.

Truss: A truss is a frame that uses
triangles by linking them together.
There are 3 types of Trusses. The
first is a Pratt Truss which uses
right angle triangles. The second
is a Warren Truss which uses
equilateral or isosceles triangles.
The third is a Howe Truss which
uses many different triangles but
are reflected over a line in the middle
of the triangle shape.

Gusset: A gusset links the triangles in
a Truss together. A gusset is a solid
material that reinforces the vertices
and joints together. Gussets are used
to resist compression, tension or
torsion forces.

Curves make arches and architects like
to use arches because they use less
material which makes them cheaper
and they are strong. Architects may use
a inward reaction which puts the arch
under the force of compression. Or they
may choose to use a outward reaction
that puts the arch under compression.

Ties: Ties are used to give a minor
stability to a structure to give the
reinforcement it needs. A tie works
under the act of Tension.

Struts: Struts are used to give a minor
stability to a structure to give it the
reinforcement it needs. A strut works
under the act of Compression.

If you look through an edge of a cardboard
shipping box you will see that there are
arches holding up the two cardboard
surfaces. This is called corrugation.
Corrugation is better at resisting compression
than a flat piece of cardboard or paper.

When you make a material thicker you laminate
it. Adding layers of the same material will make
the material stronger. So, to save money,
Architects laminate their materials and it makes
them strong and reinforced, making their
structure more stable.

The plane of application is the angle
that force is being applied to on an
object. If I push a tea cup on a
horizontal angle it will most likely
topple over and break but if i push
on a 180 degree angle it will slide
across the surface.

The point of application is the point
on the object where the force is
being applied. So if I push a
perfume bottle from the top it will
topple over and if I push it from
the bottom it'll stay sturdy and move
in the direction I push it to.

The direction where the force is applied is the
direction that the object will move. For Example,
if I kick a soccer ball to the left the soccer ball
will very likely go to the left unless the wind is
stronger than my kick and will push the ball to the
right.

Magnitude is how strong the External Force
is. If you have a stronger external force then
the object receiving the force will be more
damaged or moved faster. For example, If
I were to slap my older sister with as much
force as I can it would definitely hurt but
my older sister is much stronger than me so
if she slapped me with all her might I would
fall to the ground and be more damaged.

Compression is the force of pushing in
an object. When you hug a stuffed
animal really tight it is under
compression because it's forces are
pushing in the opposite way.

Tension is the force of pulling in an
object. When you pull a tight sweater
over your head the material is under
tension because it is being pulled in
two opposite directions.

Torsion is another word for twisting. Torsion
can happen in two different ways. The first
way is twisting both ends of an object in
opposite ways. For example opening a
tough jar. One hand is placed in the
middle of the jar and the other is on the
cap twisting in different directions. The
second example is twisting one end of an
object. For example twisting a barbie dolls head
and keeping her body in place.

A shear force is when you pull apart an object
by pulling or ripping at two different points and
ripping in two opposite directions. For Example,
when you have one full chicken nugget and rip
it apart so you and your sibling can each have
a fraction on the full chicken nugget.