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Forces And Structures > Test 1 > Flashcards

Test 1 Flashcards

1
Q

Define stability using these terms: stable, centre of gravity, support base and support points

A

A structure is stable if it remains on its base when acted on by forces its designed to withstand. When you support an object at its centre of gravity, the area that the mass of the object is being concentrated, the object is perfectly balanced. A structure will only remain stable if it’s centre of gravity is between the support points. If centre of gravity is located outside support base, structure will fall.

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2
Q

The tower of Pisa is a very unstable structure. What are two ways people have tried to add stability to it?

A

In 1934, people attempted to inject concrete under the tower and it made it significantly worse.
A plan scheduled 1999-2000 wanted to brace tower with cables and remove some soil under the north side.

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3
Q

What is symmetry

A

An object or structure is symmetrical if it can be divided into two by a line or plane in a way that creates two sides that are mirror images of eachother

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4
Q

How does symmetry effect the stability, loads, and cost of a structure

A

Stability: a structure that has its centre of gravity over the centre of its support base can resist external forces better than a structure that does not
Loads: if the load is symmetrical on both sides, supports must only deal with a compression force and will not break
Cost: not very expensive! Can be mass produced because no need to custom design each part

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5
Q

Give example of symmetrical and non-symmetrical structure

A

Symmetry: human face, chair, seesaw,
Not symmetrical: bikes, coffee cups,

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6
Q

Describe shell structure

A

Solid surface, hollow interior
Can be made of weak material
Useful for protection and containers

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7
Q

Describe mass/ solid structure

A

Only 1 part
Strength comes mainly from mass
Stronger than shells
Used mostly as supports
No hollow spaces

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8
Q

Describe frame structure

A

Formed from combo of parts
No components of the frame structure are capable of holding load alone
Good at handling torsion and tension

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9
Q

What are natural vs manufactured structures?

A

Natural are what is made by nature. Ex. Eggshells, trees, wasp nest, anthill, snowflake
Manufactured are human made, ex. Skyscrapers, bike, parachute, paper cup,

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10
Q

Give and example of a natural and manufactured structure for each type of structure. Also a combo that uses all three

A

Shell: eggshell, parachute
Frame: spider web, bike
Mass: mountain, concrete block
Combo: human body:skull, femur, skeleton

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11
Q

How to calculate structural efficiency

A

SE= mass supported
————————
Mass of structure

Or mSup
And mStr

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12
Q

What units are used to calculate SE

A

SE doesn’t have units

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13
Q

Give ex of SE

A

Our egg shuttle drops. The goal was to have the lightest structure and also to protect the egg.

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14
Q

Define tension

A

Pulling or stretching force on an object

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15
Q

Define compression

A

Pushing force that squeezes on an object

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16
Q

Define shear

A

Top and bottom act in different directions and part tears along flat plain

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17
Q

Define torsion

A

Created by applying opposite rotational forces on different parts of a structure

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18
Q

Give an example of each internal force being used in our daily lives

A

Shear: using scissors
Torsion: wringing out a towel
Tension: playing tug of war
Compression: squeezing a fidget toy

19
Q

Give an example of a situation in which each internal force causes a structure to fail

A

Tension: pulling on a rubber band and it snapping from pulling it too hard
Compression: balancing across a beam but beam snapped under your weight
Shear: pulling apart a piece of paper with too much force
Torsion: When sections of the structure slide past each other the structure can crack or break in two

20
Q

Define load, static load, dynamic load, dead load and live load.

A

Static load: caused by force of gravity
Dynamic load: caused by any other force
Dead load: caused by the force of gravity acting on the structure itself
Live load: weight of gravity pulling on whatever is on the structure
Load: the forces acting on a structure

21
Q

What 5 things do designers and engineers consider when designing a structure

A

Function
Aesthetics
Safety
Materials
Joints

22
Q

List 5 different functions of structures

A

Containing
Sheltering
Supporting
Lifting
Fastening

23
Q

Why are aesthetics important

A

The best designs look good. Designers refer to such designs as aesthetically pleasing. Much rather visit a beautiful looking building than an ugly one

24
Q

What’s the margin of safety

A

Having a large margin of safety means that the structure can withstand loads much larger than it needs to. This keeps it safe so that if an elevator got slightly overcrowded it would still be safe and not crumble.

25
Q

How do Costs and materials impact design?

A

Making structures stronger Costs more
Bigger, stronger parts use more material
Skilled craftspeople cost more than inexperienced workers
Good design is a compromise between reasonable margin of safety and reasonable cost

26
Q

Define span

A

A section of bridge that lies between 2 supports

27
Q

Describe beam bridge

A

Consists of 1 or more beams supported on both ends and sometimes by columns underneath

28
Q

Describe truss bridge

A

Usually made of steel, relies on a system of triangular supports (trusses) to support its load

29
Q

Describe Arch bridge

A

Supports its load from below (concrete or stone) or above (steel). Static load creates a compression force in the arch

30
Q

Describe suspension bridge

A

Uses cables strung from towers to support the bridge from above. Steel cables and concrete towers are used because of the enormous load created by weight of the bridge

31
Q

Describe cantilever bridge

A

Works like 2 seesaws connected by a span. Mass on either end supports the mass of the span in the middle. Made of massive steel girders supported by concrete piers

32
Q

Describe a situation where each type of bridge would be effective

A

Suspension: 5000 ft span accross an ocean with lots of big ships coming and going
Beam: 120 ft span accross freeway
Arch: 500 ft span across gorge
Truss: 300 ft train bridge
Cantilever: across large span of water

33
Q

How can internal forces cause a bridge to fail

A

Materials fail, design flaws

34
Q

How can external force cause a bridge to fail

A

Earthquakes, winds, floods

35
Q

What are advantages and disadvantages of each type of structure(shell, mass, frame,

A

DF: cannot handle compression well
AS: force distribution
AM:very heavy can hold down many things
AF: only works when linked together with counterparts,
DURABLE AND COST EFFIECIENT
DS: little pressure needed to break
DM: very heavy, can only be used for its weight

36
Q

How do structures fail? Use: internal forces, external forces, structural fatigue.

A

Internal and external factors can cause a structure to fail, as well as structural fatigue, which is just a structure getting old and not operating how it used to

37
Q

What 7 techniques are used to make structures stronger

A

triangles
Curves
Ties
struts
Gussets
Corrugation
Lamination

38
Q

Describe trusses with example

A

A frame that takes advantage of the strength of triangles by linking many of them together
Warren truss vvvvvvv
Truss bridge

39
Q

Describe gussets with example

A

A piece of solid material used to reinforce the triangle.
Used to resist tension, compression, or torsion forces

40
Q

Describe curves with example

A

Arch channels force caused by load to supports of the arch
Arch bridges

41
Q

Describe ties with example

A

Tie does it’s work by resisting tension forces
Supports on a sign

42
Q

Define struts with example

A

Similar to ties, but resists compression forces
Supports on sign

43
Q

Describe corrugation with example

A

Waves that act like series of arches
Cardboard

44
Q

Describe lamination with example

A

Bonding of 2 or more materials together
A kitchen counter that had a waterproof material laminated to it

Forces And Structures (1 decks)

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