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Chapter 6

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

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  1. Chapter 6 Designing Structural Systems

  2. 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.

  3. Natural Structures • Human Body • Beehives • Snail shells • Spider Webs • Ant Colonies (hills) • Termite trails

  4. Technological Structures • Bridges • Homes • Skyscrapers • Domes • Roads • Phones • Computer Cases

  5. 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.

  6. Failures (cont.) • Safety Factor - determines how much a product or an element within a product is overbuilt.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. Calculating Loads • Physical Models • Mathematical models • Computer models • Vector Analysis • Graphical Analysis • Bow’s Notation

  12. Why is all this Important?

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