1. What is structural technology?

2. What comes to mind when you hear the word “structure”?

DRILL

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April 27, 2011

• The technology of putting mechanical parts and materials together to create supports, containers, shelters, connectors, and functional shapes.

Example applications: • Legs on a chair, • City water tower, • Swimming pool, • Roadways and Bridges, • Bicycle spokes• Airplane wing, • Satellite antenna disc.

Structural Technology

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Structural Technology

Structural engineers are responsible for structural integrity.

1. Structural failures do not occur very often, but when they do, we hear about it:a. Tacoma Narrows bridge (1940)b. Challenger Space Shuttle (1986)c. Columbia Space Shuttle (2003)d. Chernobyl Nuclear Reactor (1986)e. 2007 Missouri bridge collapse

2. As late as 1870’s and 1880’s, 25 bridges a year collapsed on the American roadways.

3. Many people can be killed when engineered structures fail.

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Structural Technology

Almost everything is a structure of some kind:

HumansPlantsAnimalsHousesVehiclesTablesBottles

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• Galileo Galilei (1564 – 1642)• The “Father of Modern Physics”• The “Father of Modern

Science”• Research into the strengths of

materials• Prior to Galileo, the size and

shape of most structures was determined by the traditions and rules of highly skilled craftsmen.

The “First Modern Engineer”

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• Structural designs advanced by trial and error until modern engineers were able to anticipate the characteristics of new buildings, bridges, and other structures.

• Engineers apply science and mathematics to the problem of designing safe structures.

• Many engineering principles are based on common sense.

Structural Technology

Structural TechnologyNewton’s 3 Laws of Motion:

1. Inertia: objects at rest stay at rest;

objects in motion stay in motion

2. F = ma: Force equals mass times acceleration

3. Action/Reaction: for every action there is an equal and opposite reaction

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Structural Technology

• Another way to look at it:– How much do you weigh?– You are pushing down on the earth that amount of force.– The earth is pushing up on you with an equal amount.

• What would happen if the earth were pushing up with more force?

• Less force?

• Strength of a construction material is the capacity to support loads by resisting the 4 structural forces.

• Strength depends on materials’:– Type– Size– Shape– Placement

Strength of Materials

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Structural Forces

• Four types of force exert stress on building materials:–Compression – push; tends to flatten/buckle–Tension – pull; tends to stretch–Shear – slide; material fractures–Torsion – twist; twist out of shape or fracture

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Structural Forces

TensionU3j - L1

Structural Forces

CompressionU3j - L1

Structural Forces

Torsion

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Structural Forces

Shear

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Structural Forces

Compression

Tension U3j - L1

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Strength of Materials

Is bending one of the structural forces?• Deflection – bending that results from both

tension and compression acting on a member at the same time.

– Vertical– Horizontal

TENSION

COMPRESSION

COMPRESSION

TENSION

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Strength of Materials

– No deflection

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Structural Forces

A structure must contend with two types of loads:

1. Dead Loads: permanent loads that do not change.

The weight of building materials and permanently installed components:

Lumber, brick, glass, nails, steel beams, concrete

2. Live Loads: the weight of all moveable objects, such as people and furniture in a house, vehicles on a bridge.

Includes weight of snow, ice, dead leaves, and force of winds.

The total weight or mass of all live and dead loads is the Total Load.

Structural Forces

A building supports the following loads in the middle of winter:• 10,000 lbs of lumber• 1000 lbs. of snow and ice• 40,000 lbs of brick• 300 lbs of wind• 600 lbs of glass• 200 lbs of nails

1. Calculate the Live Load.

2. Calculate the Dead Load.

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Live Load:

1000 lbs.

+ 300 lbs.

1,300 lbs.

Dead Load:

10,000 lbs.

40,000 lbs.

600 lbs.

+ 200 lbs.

50,800 lbs.

Structural Forces

1. Live Load = 1,300 lbs.

2. Dead Load = 50,800 lbs.

3. Calculate the Total Load:

Total Load = Live + Dead Load

= 1,300 lbs. + 50,800 lbs.

Total Load = 52,100 lbs.

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Classwork

• Pick four pieces of technology that have a structure.

• For each structure, describe if the members of the structure are designed for compression, tension, torsion, or shear or some combination of the four.

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