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Table of Contents • • Content Standards • Handouts Title Page Lesson Title Forces and Loads Objectives Static Loads Dynamic Loads Guiding Questions Live Loads Dead Loads Materials Tension Compression Activities Tension and Compression (Images) Shear References Shear (Image) Torsion (Images)
Standards for Technology Education Construction Systems WVEIS 2424 Standard 7: Forces and Loads (2424. S. 7) Students will identify and examine the forces and loads acting upon structural elements. Forces and Loads Objectives Students will: 2424. 7. 1 Differentiate between the forces that act on structures (tension, compression, shear, and torsion), and determine which forces are present in various structural elements. 2424. 7. 2 Differentiate between static, continuous dynamic, and impact dynamic loads, and give examples of each.
Lesson Title Forces and Loads George Washington Bridge, NYC
Objectives After performing several small activities and studying with the handouts the students will be able to distinguish between different forces that are present in various structural elements and will have basic knowledge of different loads that act on structures.
Guiding Questions • Which forces have you already heard of? • Where do loads on structures come from? • Why is it important that Engineers understand the basic principles of physics? • Can you think of a simple, every day example where we can find tension and compression? • Do you know of any structures that have collapsed?
Materials • Rubber band for each student • Marshmallow for each student • Handouts – (alternatively the applicable slides can be presented in form of a Power. Point presentation)
Activities • Tension: – Students are to link their hands together and pull. They will feel tension. – Let students stretch a rubber band. They see tension in action. The rubber stretches, and the band gets longer. It's in tension. • Compression: – Have students put their hands together and push hard. They will feel tension – Give each student a marshmallow to put on the table in front of them. As they push it down with their hand, the marshmallow gets shorter because it is in compression.
References – http: //www. adl. gatech. edu/classes/dci/structur/dci 08. html – http: //www. answers. com/topic/shear-stress? cat=technology – http: //wwwgeology. ucdavis. edu/~GEL 1/W 03_verosub/G 1 Hwebsite/buildinggroup/ Andrews/challenges. html – http: //www. enm. bris. ac. uk/research/nonlinear/tacoma. html
Forces and Loads George Washington Bridge, NYC
Forces and Loads • Forces that act on structures are called loads • Loads on structures come from three main sources: – Structure weight – Occupants or users – Natural elements
Loads • Two main categories: – Static Loads • The effect of the load on a structure – Dynamic Loads • The permanence of the load
Static Loads – Static loads change slowly or are motionless – Static loads can include: • The weight of the structure • The weight of its occupants • Any furniture or machinery
Dynamic Loads • Change rapidly or move unpredictably • Dynamic loads can include: – Wind – Waves – Earthquakes – Traffic over a bridge
Live Loads • Anything not permanently attached to the structure • Can be moved or changed over time • Live loads from natural elements: – Snow, Winds, earthquakes, water • Live occupant loads: – People, Furniture, Machines
Dead Loads • Weight of the structure itself • Includes all structural elements and components, such as – Roof – Walls – Floors – Foundation
TENSION- The Pulling Force • Stretches materials apart • Look for materials in tension in: – – Rope and suspension bridges Telephone wires Tents Steel cables supporting a full elevator
COMPRESSION - The Pushing Force • Compression pushes materials • Look for materials in compression in: – Pyramids – Telephone poles – Arch bridges
Tension and Compression
SHEAR – The Sliding Force • Shear causes parts of a material to slide past one another in opposite directions
A road destroyed by shear
TORSION – The Twisting Force • Torsion is the force that twists a material
Tacoma, Washington, 1940 Torsion movement, twisting motion