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Physical Science Applications in Agriculture

Physical Science Applications in Agriculture. Unit Physical Science Systems. Problem Area. Agricultural Structural Systems. Loads and Loading: Designing a Free Span Structure. Lesson. Why do buildings fail?. Discuss causes of building failures.

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Physical Science Applications in Agriculture

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  1. Physical Science Applications in Agriculture Unit Physical Science Systems

  2. Problem Area Agricultural Structural Systems

  3. Loads and Loading:Designing a Free Span Structure Lesson

  4. Why do buildings fail? • Discuss causes of building failures. • Describe failed buildings they have seen and to speculate on possible causes of the failures. • Prepare a list of loads buildings are designed to withstand.

  5. Learning Objectives • Define loads. • Describe dead load, live load, snow, and wind loads. • Locate tension, compression, shear, and torsion forces in a free span structure, and determine how these correlate with the identified failure points.

  6. Terms • Dead load • Live load • Load • Snow load • Wind load photos.wholesomebalance.com/a-Winter.html

  7. What are loads? • Webster defines “load” as “an amount carried at one time.” • For these applications within this lesson “load” will be defined as the forces that act upon the structural members of a building.

  8. What are loads? • Loads create a force on a structure. • The total load on a building is made up of dead load and live load. www.rwdiwest.com/aspx/pub/Misc/MiscPage.aspx?pg=118

  9. What are loads? • Have students look around the room and make a list of as many different loads affecting the room as they can. • Do all loads act as forces to the room? • Explain why or why not?

  10. TENSION, COMPRESSION, SHEAR, AND TORSION IN A BEAM

  11. What are dead loads, live loads, and snow and wind loads? • Loads can create forces onto a structure. • Four basic types of loads act on structures. www.disaster-management.net/flood.htm

  12. What are dead loads, live loads, and snow and wind loads? • Dead load of a structure is the weight of the materials used to construct it. In a given structure the dead load is constant in amount, and it acts vertically downward. www.americansteelsystems.../hayphotos.htm

  13. What are dead loads, live loads, and snow and wind loads? • Live load consists of snow, wind, and stored materials. Loads from stored products such as grain, hay, equipment, and livestock always act downward on the various parts of a building. • The load depends on the unit weight of the material.

  14. What are dead loads, live loads, and snow and wind loads? • Snow load acts vertically downward on the roof of a building. Its intensity varies with the geographical location and the slope of the roof. www.crrel.usace.army.mil/.../roofd.html

  15. What are dead loads, live loads, and snow and wind loads? • Wind load always acts perpendicularly to the earth’s surface, perpendicularly to the side surfaces of buildings. • The load depends on many factors, such as wind velocity, height, slope of the building, and orientation of the building with respect to the wind

  16. What is the load?

  17. How can we design structures to balance and/or control forces (tension, compression, shear, and torsion) imposed by loads? www.vanerp.net/peter/.../sierpe_suspension.htm

  18. Designing Structures • In addition to the strengths of various building components (trussed rafters, pole embedment, and bracing), weaknesses or strengths also result from materials used, construction practices, or misuse of known design recommendations. • Building failures caused by large snow and wind loads generally result from inadequate design or carelessness in construction.

  19. Designing Structures • One obvious cause of failure is wide spacing of trusses. • Raising the lower chord in trusses to gain another foot of head room is usually a mistake. • The strength of the roof is limited to the strength of the upper chord from the plate up to the lower chord.

  20. Wind Loads • An 80 mph wind causes a net uplift load on each truss: about 1200 lbs. on 50' trusses 4‘ o.c. trusses must be securely anchored. • A study of storm-damaged farm buildings had not considered fastenings such as adequate roof anchoring. • Good fasteners properly applied add little to the cost of a building but can prevent complete building failure or at least reduce the damage.

  21. Wind Loads

  22. Wind Loads

  23. Building joints are often particularly weak. • Splices and joints often fail from inadequate fasteners. • Initial failure in trusses from snow load is often in the bottom chord. Excess tension causes joints to fail or the member to fail at a knot or split. • Use 2 high quality lumber in the bottom chords. Do not splice chord members at the panel points. • Lower grades of lumber than recommended are noted in many failed buildings. Knots and splits can cause main members to fail.

  24. Review/Summary • What are loads? • What are dead loads, live loads, and snow and wind loads? • How can we design structures to balance and/or control forces (tension, compression, shear, and torsion) imposed by loads?

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