1) Forces and Stresses (UNIT 4 - Structures)

What is a structure?

• A machine that produces motion
• Any system of interconnected parts designed to support a load
• A device that measures forces
• An element that only carries electricity

Which of the following is an example of a structure?

• An electrical circuit
• A written essay
• A tower or bridge
• A math equation

The main purpose of a structure is to...

• Change chemical properties of materials
• Withstand loads and forces while maintaining stability
• Make objects lighter
• Move objects through space

Which statement best describes a fixed (permanent) load?

• A load that changes depending on the weather
• A load that changes based on user activity
• A constant load that does not change over time
• A load that acts only during earthquakes

An example of a fixed load is:

• Pedestrians on a footbridge
• The weight of the concrete in a bridge deck
• Cars driving on a highway
• Wind pressure on a building

Variable loads are loads that...

• Stay the same all the time
• Are always caused by natural disasters
• Change over time or vary in magnitude
• Must be heavier than fixed loads

Which is an example of a variable load?

• The constant weight of steel beams in a building
• The daily traffic load on a roadway bridge
• The mass of concrete in a building foundation
• The weight of a statue in a park

Tensile forces...

• Push materials together
• Cause materials to twist
• Pull on a material, attempting to elongate it
• Slide parts of a material past each other

A good example of a tensile force is found in:

• The pillars of a skyscraper
• The cables of a suspension bridge
• The base of a signpost struck by a car
• The wind blowing against a tree

Compressive forces...

• Stretch materials
• Push materials together, reducing their length
• Have no effect on materials
• Cause materials to twist along an axis