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?