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Chapter 6. Designing Structural Systems. Terminology. Structure – a body that will resist external forces without changing its shape, except for that due to the elasticity of the material.

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Chapter 6

Chapter 6

Designing Structural Systems


Terminology
Terminology

  • Structure – a body that will resist external forces without changing its shape, except for that due to the elasticity of the material.

  • Structural systems – systems in the natural and technological world that provide a means of stability and foundation for mobility.


Natural structures
Natural Structures

  • Human Body

  • Beehives

  • Snail shells

  • Spider Webs

  • Ant Colonies (hills)

  • Termite trails


Technological structures
Technological Structures

  • Bridges

  • Homes

  • Skyscrapers

  • Domes

  • Roads

  • Phones

  • Computer Cases


System failures
System Failures

  • Planned Obsolescence – the name given to the concept of planning the failure of a technological product after a certain amount of use.

  • Durable goods – products that are intended to last more than three years.

  • Non-durable goods - products that are designed to not last more than three years.


Failures cont
Failures (cont.)

  • Safety Factor - determines how much a product or an element within a product is overbuilt.


Forces on structures
Forces on structures

  • Static Loads – loads at rest.

  • Dynamic Loads – forces in motion.

  • Internal forces – the molecular makeup of a material to counter external forces.

  • External forces - loads that are applied to an object in question.

  • Equilibrium – when internal and external forces are equal.


Stress and strain
Stress and strain

  • Stress – the strength of a material (when an object will fail or break).

  • Strain – the change in shape of a material caused by compression or tension forces (how far the material stretches under a load).

  • Young’s Modulus of elasticity - the measure of stress and strain of a material.

    • Elastic stage – point 0 to A where a material will change shape, but return to normal.

    • Plastic stage - point B, where a material will remain in its strained shape and not return to normal.

    • Breaking point – point C, where a material fails or breaks.


The five common forces
The Five Common Forces

  • Compression – The inward forces on an object (pressing down or in).

  • Tension – the outward forces on an object (the pulling apart of something).

  • Bending – when the forces are acting across the entire material (both compression and tension).

  • Shear – forces acting in opposite directions but in the same plane

  • Torsion – forces that try to twist a material apart.


Structural components
Structural Components

  • Beams – Horizontal members that are designed to resist compression and bending forces. (fig. 6-20) pg 125.

  • Trusses and Girders – complex beam designs.

  • Struts – components that resist compression (piers and columns)

  • Ties – components that resist tension (cables or rigid steel elements).

  • Fasteners – Mechanical: rivets, bolts, screws and nails; chemical: welds and glues


Calculating loads
Calculating Loads

  • Physical Models

  • Mathematical models

  • Computer models

  • Vector Analysis

  • Graphical Analysis

  • Bow’s Notation



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