9
Tension Compression Torsion Bending
Architectural engineers often use
five terms to describe how a load
can affect a structure: tension,
compression, shear, torsion, and
bending.
Tension is any force that pulls (or
stretches) an object apart.
Compression is any force that
pushes in on (or squeezes) an
object.
is a force that causes parallel
internal surfaces within an object
to slide past each other.
Torsion is a force that causes
the twisting of an object due to a
moment.
Bending force is a force that
causes an object to bend.
A force is an interaction between objects. You can
think of a force as a push or pull on an object that
changes the motion of that object. If the object
resists that motion, the object might deform — part
of the object might move relative to another part
of the object rather than the entire object moving.
Architectural engineers must analyze the forces acting
on buildings to make sure the buildings will stay
standing. Forces acting on a building are called loads.
Pull on the exible rod from both ends. It’s very strong
intension, isn’t it?
Now push both ends together. It’s not very rigid in
compression. It buckles when you push the ends
together. In terms of shear, it’s pretty resilient. And when
you subject it to torsion by twisting it, it twists.
Hold one end of the rod and push down on the middle.
The rod bends. One side of the rod is under tension and
the other side is under compression.
This is a special type of plastic that is designed to have
just the right amount of exibility for building the
models in this kit. These exible rods are used in the
models to mimic steel beams in real buildings.Like
plastic, steel is incredibly strong under tension but it isn’t
so great under compression. It will bend under too much
force, but it’s very hard to pull it apart from end to end.
Why aren’t more buildings built with plastic rods? Steel
and other metals are much more resistant to heat and
less likely to degrade under normal conditions. Steel is
stronger, harder, and more durable than plastic.
Plastic and Steel
Loads Acting on a Building
Architects must design buildings to withstand many
different types of loads that could pull them down
or push them over. Loads can be divided into two
categories: Dead loads and live loads.
include the weight of the building itself
and all the permanent things installed in the building.
Gravity pulls these loads downward.
include the weight of the people, furniture,
and other objects inside the building. The snow load
and rain load — the weight of the snow or water on the
roof — are also live loads.
Some live loads act laterally on the building, instead of
pulling downward. The wind load is caused by the wind
pushing on the side of the building. The groundwater
and earth around the building’s foundation push
laterally on it. And even the load from occasional
earthquakes must be considered when designing a
strong, stable building.
Wind
Load
Load
Water and
Earth Pressure
Lateral Loads
