1. Structural Stability and Strength
Making it Work

2. Stability
Stability is the ability of a structure to maintain, or regain, a balanced position when external forces act on it.
A stable structure maintains it position and shape over an extended period of time
An important factor in maintaining stability is an object’s centre of gravity
Centre of Gravity: the point around which a structure’s mass is equally balanced in all directions; the point where the mass seems to be concentrated

3. Making Structures Strong
The Beam

4. What’s a beam?
A beam is any reasonably level structure that is designed to support a load
A doorway consists of:
a horizontal upper beam
two vertical supports

5. Strengthening the Beam
On its own, a beam might not be strong enough to support a large load
Beams can be strengthened in many ways
It can be as simple a choosing a stronger material, steel is stronger than wood, but also heavier
Sometimes engineers use other ways to strengthen beams

6. I-Beams One way to strengthen a beam is to change its shape
An I-beam is stronger than a normal beam

7. Corrugation Folding a beam also adds strength
Placing triangular ridges, grooves, or folds in a structure is called corrugation
Common in cardboard, and in plastic and metal for roofing

8. Rebar
Concrete beams are often strengthened with steel rods called rebar
Beams experience compression on top and tension on the bottom
Concrete can handle a lot of compression, but not much tension
Rebar solves that problem when it is added
This is called reinforced concrete

9. Cantilevers Cantilevers are beams that are only supported at one end
Tree branches and diving boards are simple examples of cantilevers

10. Supporting Cantilevers
These supports are all built into the framework of a cantilever to strengthen it
Tie: designed to resist tension
Strut: designed to resist compression
Gusset: flat, plate-like, often triangular, supports the connection to the support base

11. Making Structures Strong
The Truss, Arch, and Dome

12. Making it stronger… and more interesting
Sometimes designers want to use shapes other than beams to make structures stronger and more interesting looking
They do this by using triangles (trusses) or curves (arches and domes)

13. The Truss A truss is a network or beams that form triangles
A truss can be used as a bridge or a cantilever, and many other applications
Most people are familiar with trusses used in roof construction for houses, construction cranes, hydro towers, and bridges
Trusses can be bent and still retain their strength
The triangles help the structure support more weight
Trusses can be used for things that beams can’t

14. STOP!!
Build a Truss

16. The Arch An arch is a curved structure often used to support loads
They’re used in spaces where supporting beams are not practical
It transfers compression force downwards
Many early civilizations, like the Romans, used arches a lot. Some, built over 2000 years ago, are still standing

18. The Dome
A dome is a structure that looks like the top half of a sphere or an egg
Like an arch, a dome directs compression force downward
Unlike an arch which directs force along only one plane, a dome directs it down many planes
You could consider a dome to be a series of arches connected at a centre point

20. Geodesic Dome