GRADE 7: Types of Structures
STRUCTURES
A structure is something which will support an object or a weight. It can also be described as anything that
provides support and is made from one or more parts. When classifying structures by design they can be
divided into three groups: frame, solid and shell structures.
1. SHELL STRUCTURES
In a shell structure the outside layer of the structure holds the whole object together. Tins or cans are shell
structures. The weight of the liquid or food inside is supported by the skin of the container.
Examples of shell structures are: ____________________, ______________ ,________________.
Did you know? The Taj Mahal roof in India and the Sky Dome roof in Toronto are examples of shell structures .
Sketch a Shell Structure:
2. FRAME STRUCTURES
Frame structures have a rigid arrangement, or framework, made up of parts fastened together, called structural
components. A frame structure can be arranged in 2 dimensions, as in a door frame or fence. A frame
structure can also be organized in 3 dimensions, as in the frame for a music stand or the wood framing for a
house.
Examples of frame structures are:_________________, _________________ ,_________________.
Did you know? The Greek Parthenon and the Eiffel Tower and the Empire State Building are all examples of
frame structures .
Sketch a Frame Structure:
3. SOLID STRUCTURES
Solid structures are sometimes called mass structures and are usually made from one solid piece of a strong
material. A solid structure has little or no space inside and relies on its own mass to resist the forces that act
upon it.
Examples of solid structures are:_________ ________, _________________ ,___________________.
Did you know? The Egyptian pyramids and the CN Tower and the Great Wall of China are all examples of solid
structures .
Sketch a Solid Structure:
MASS, WEIGHT AND LOAD
Mass, weight and load are important terms but they can be confusing. To help you remember here’s
a trick!
Think about holding a handful of identical marbles.
Mass: The quantity of matter in an object. Commonly measured in grams or kilograms.
The amount of matter in an object and would be represented by the number of marbles in your hand.
The mass of the marbles might be 500 grams.
Weight: The force of gravity acting downward on an object. Measured in Newtons (N)
The force of the earth’s gravity acting upon the object. It is how heavy the marbles feel on earth.
Weight depends on the magnitude of the gravitational pull. The weight decreases farther away from
the earth you go. What would happen if you took the marbles to the moon? Well, the moon has less
gravity, so the marbles would weigh less, but the mass would not change.
Load: A force acting on a structure. In this case, the force would be gravity.
There are two types of loads:
Live Load:
A type of static weight caused by the weight of the object it supports (Weight of the man on the
bridge)
Dead Load:
The static load caused by the weight of the structure itself (Weight of the Bridge)
FORCES
There are two types of forces:
1) External Force:
A force acting on an object or structure from the outside. Ex. Wind, Gravity
2) Internal Force:
A force acting within the structure. There are 4 different types:
a) TENSION
If we take a material and try to pull it apart from either end, we are putting it into tension. A tow rope
for a water skier
has to resist the forces of tension. Tension is a pulling force. The coping saw blade is held in tension.
b) COMPRESSION
Compression is a force that tends to press a material - a squashing force.
Ex. The springs in a mattress compress when you lie down.
c) TORSION
Torsion is a turning or twisting force.
Wind for example, can exert torque on bridges, especially on suspension bridges.
d) SHEAR
Shear force acts in an object as a result of pushes and/or pulls in opposite directions. A strong wind
can cause a shear force within a tree and can cause it to snap.