Structures

Structures: Form and Function
Structure - made up of any parts that serves some kind of purpose
Function - its purpose (e.g. a bird’s wings allows it to fly)
Form - how the structure’s components are shaped & arranged together.
        - the form serves its function.

Consolidation:  the process of becoming or being made stronger and more certain

Materials are chosen for their properties (strength, hardness, resistance to corrosion)
- chosen based on cost, property, quality, availability & impact on environment.

Composite materials combine various materials to take advantage of each other’s property.

Layered materials are when materials are placed on top of one another & pressed or glued together.

Woven, knit & pressed materials are twisted, spun, looped or knotted.

Forces Acting on Structures
Forces: A push or pull
- Can be contact or non-contact force
- Measured in units

Gravity: the force of attraction between objects, it’s most noticeable when an object has a large mass
- A non-contact, pulling force
- If we lift up an object, we are overcoming the “downward” pull of Earth on that object. In other words, the force we use on the object is greater than the force of gravity pulling it down.

- Forces have a magnitude & direction.
Magnitude: how big the force is compared to the size & weight of the object
Direction: where the force is coming from/where the force is going

- Forces we exert are called applied forces
- the force that pushes upwards against gravity is called the normal force
- in diagrams, forces are represented by arrows. The thickness of the arrow indicates the magnitude & the way the arrow points indicates its direction.

- All objects have at least 2 forces acting upon it at any given time
- If an object is not moving, then the forces acting upon it have the same magnitude. In this situation, we’ll call the forces “balanced forces”.

If the forces acting upon an object have different magnitudes, then the forces are considered to be unbalanced forces & the object moves.

Mass vs. Weight
Mass: the amount of matter in an object
- Measured in grams or kilograms
- does NOT change because of gravity

Weight: amount of force on an object due to gravity. The amount of force the Earth pulls an object with.
- Measured in Newtons
- In order to convert kilograms to newtons, multiply it by 9.8.

Loads
Load: a force that acts on a structure, the sum of the static & dynamic load.
Static Load:
- constitutes forces that resulted from gravity
- dead load is the weight of the structure itself
- live load is the weight of the object a structure supports

Dynamic Load: caused by forces outside of gravity

Extraordinary load: A load that is not within the expected range in a certain region

Forces (yay) PART 2
External forces - force on an object from outside of the object
Internal forces - forces caused by 1 part of a structure acting on other parts of the structure (e.g. compression, tension, shear, torsion)

External force is a structure that acts on a structure from outside the structure (e.g. gravity, wind, earthquakes)
- includes the load

- a structure must be designed so that external forces do not cause it to break or fall over. The point of application and the plane of application must be considered.

Point of Application: an imaginary flat surface through which an applied force passes
- if the point of application is lower on the cabinet, it will slide sideways. If the point of application is high on the cabinet, it could tip over

Internal forces - a force acting within the material of the structure
- Internal forces must be great enough to balance the stress of large loads, or else it may fall apart or deform.

Tension forces cause a material to stretch by pulling its ends apart
Tensile Strength - a measure of the largest tension force that a material can take before changing shape/breaking.


Compression Forces squeeze a material together.
Compression Strength - a measure of the largest compression force a material can withstand before changing shape or breaking.

Shear forces cause a material to tear, bend or break by pushing/pulling in opposite directions within an object
Shear Strength: A measure of the largest shear force that a material can withstand before it tears apart.

Torsion forces act when an object is twisted by turning its ends in opposite directions.
Torsion Strength measures the largest torsion force a material can withstand & still spring back to its original shape
- point of application is usually on opposite ends

Structural Stress: Effect of all the internal and external forces acting on a structure over a long period of time.

Structural Fatigue: Permanent changes due to the internal and external forces acting on it.

Structural Failure: Breakdown of a structure due to the internal & external forces acting upon it.

How structures can fail
Structural failure is when a structure or part of it loses the ability to support a load. Under certain conditions, the forces acting on a structure can cause structural failure.

Extreme conditions such as pressure, temperature & humidity can cause unexpected forces that cause structural failure.

Material failure can occur by deforming or fracturing.
-Tension can cause it to snap
- Torsion can cause it to fail by twisting
- Compression forces squeeze materials & can shear
- Rigid materials fracture while flexible materials deform

Foundation failure: damage to a structure’s base or foundation can cause a structure to fail
- if not firm, it can shift the structure causing instability or failure of the structure
- The thrust line of a structure is a vertical line drawn from the center of the ground. If it passes through the base of the structure, the weight will be supported evenly.
- If it passes out of the base, then it is unstable and is most likely to tip over or fall.

Stability - the ability of a structure to remain or return to a balanced position when unbalanced forces act on it.
- Structures must be designed to be stable so that they do not easily topple over or fall down.
- Symmetry refers to an exact reflection on opposite sides of a line dividing an object in half.
- Symmetry is a feature of the structures. A structure is symmetrical if an imaginary line, called a symmetry line, can be drawn that divides the structures in half to create a mirrored image of each other.
- Symmetry is aesthetically pleasing.
- Symmetry can also help with stability

Center of Gravity: the point around which a structure’s mass is equally balanced in all directions.
- Finding a structure’s center of gravity helps designers determine its stability. The whole mass of an object appears to be concentrated on the center of gravity.
- Located deep inside. (😱😨⁉)
- Changes everytime you move or bend it in different ways.
- Depends on the shape and how its mass is distributed.
- Stability is the greatest when there is a low center of gravity & a wide support base.
- Stability decreases as the center of gravity rises & is directed above the support base.

Forces are always acting on structures. Engineers & builders will often include certain things/design features to prevent structural failure.

Benefits of using I, L or Box beams:
- Less mass than solid beams, therefore have less of their own mass to support & costs less to make.

Using Triangles
- Triangles are strong, rigid & aren’t easily bent.
- Square and rectangular frames
- Can be arranged side by side to make a strong, lightweight framework

A beam is a length of material that is used horizontally to support a load.
- Can be made of various materials
- There are always pros & cons to choosing the right material.
- Beams can also be folded to give it more strength.

Corrugation: placing triangular folds, ridges or grooves.

The Cantilever - a beam that is supported on only one end
- A tree is a natural cantilever
- A balcony & a diving board is a manufactured cantilever.

Using funny shapes
Arch - like a curved structure used to support loads in spaces where beams aren’t practical or wanted.
- The curved design of an arch transfers compression forces downward to the ground. 

- Commonly used in doorways, windows, bridges & places of worship.
- The top of the arch is called a keystone.




Dome - a structure that looks like the top half of a sphere
- Like an arch, domes direct the compression force downward in many directions from a common center point. A dome is like many arches connected at their center point.
- Strong, and can enclose a large volume of space.
- Used in planetariums, stadiums & places of worship

Trusses - a network of beams & triangles.
- In a truss, forces are distributed between the points of a triangle to help support more weight while using less materials.
- Used in bridges, cranes, towers & roof supports.

Geodesic dome - A dome built from the framework of triangles.

Classifying structures based off form
Shell Structure

Frame Structure

Solid Structure

Combination Structure

Forces (PART 3)
Gravitational Force - The force of gravity, or gravitational force, pulls objects with mass toward each other.
Magnetic Force - Attraction or repulsion that arises between electrically charged particles because of their motion.
Electrostatic Force - Electrostatic force is the push or pull between charged objects. Opposite charges attract, while like charges repel.

Extra
Thrustline: An imaginary vertical line that passes from the center of gravity of a structure to the ground.
Frostline: The maximum depth underground that soil will not freeze during the coldest temperatures of the year.
- Foundations must be 150mm below the frost line.