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Lab 8 Predicting Strength of Trusses Approximate Running Time – 20 minutes

Learn how to predict the strength of trusses using ModelSmart software. This online instructional presentation covers topics such as tensile strength, compressive strength, shear strength of glue, and analyzing truss bridges.

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Lab 8 Predicting Strength of Trusses Approximate Running Time – 20 minutes

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  1. Lab 8 • Predicting Strength of Trusses • Approximate Running Time – 20 minutes • Distance Learning / Online Instructional Presentation • Presented by • Department of Mechanical Engineering • Baylor University • Procedures: • Select “Slide Show” with the menu: Slide Show|View Show (F5 key), and hit “Enter” • You will hear “CHIMES” at the completion of the audio portion of each slide; hit the “Enter” key, or the “Page Down” key, or “Left Click” • You may exit the slide show at any time with the “Esc” key; and you may select and replay any slide, by navigating with the “Page Up/Down” keys, and then hitting “Shift+F5”.

  2. Introduction Dr. Carolyn Skurla Speaking

  3. Tensile Strength Material property Measure cross-sectional area Load to failure in tension Calculate tensile strength Notes on Tensile Strength F F t w

  4. Notes on Compressive Strength • Long, thin members • Buckling will occur • Member fails in bending instead of in compression

  5. F Notes on Shear Strengthof Glue • Standard method for testing adhesive strength • Shear the glue joint y x F

  6. How to Use ModelSmart • Add Joints • On Menu, select “Joints” and make sure that “Add” has a next to it (i.e., Add is selected). • Place your truss joints on the grid.

  7. How to Use ModelSmart • Add Joints • The cursor will point to a red dot as you move it around. • When you click to place the joint, a blue dot will appear.

  8. How to Use ModelSmart • Select Size/Grade of Wood • On Menu, select “Members” / “Default Material Type” / “Balsa Wood” / “1/4” Balsa – BAL8D3”

  9. How to Use ModelSmart • Add Members • On Menu, select “Members” and make sure that “Add” has a next to it (i.e., Add is selected). • Place your truss joints on the grid by clicking on one joint and dragging to the other joint.

  10. How to Use ModelSmart • Add Members • Construct your truss bridge by adding all the truss members.

  11. How to Use ModelSmart • Add Supports • On Menu, select “Supports” and select the fixed support. Place a fixed support on one end of the truss. • On Menu, select “Supports” and select and place a horizontal rolling support.

  12. How to Use ModelSmart • Add Loads • On Menu, select “Loads” and select “Vertical Down.” • The cursor will change to a down-pointing arrow.

  13. How to Use ModelSmart • Add Loads • Place a “Vertical Down” load on the joints at each end of the top horizontal member.

  14. How to Use ModelSmart • Analyze your truss. • On Menu, select “Analysis” / “Analysis Options”. • Select “Show Displacements”, “Show Broken Members”, and “Show Stress Levels.”

  15. How to Use ModelSmart • Understanding analysis results • Red  Broken • Blue  Compression • Green  Tension

  16. How to Use ModelSmart • Understanding analysis results • On Menu, select “Member” / “Show Member Numbers” to see the assigned member number for each truss member.

  17. How to Use ModelSmart • Understanding analysis results • On Menu, select “Analysis” / “Show Results” to see the loading, strength, and efficiency ratio data for each truss member.

  18. How to Use ModelSmart • To Change Material Type • On Menu, select “Members” / “Default Material Type” / “Balsa Wood” / new grade & size of wood • On Menu, select “Members” / “Change Material Type”

  19. How to Use ModelSmart • To Change Material Type • Click on the truss member that you want to change • The changed truss member will change in size and/or color, depending on the size and class of balsa wood chosen

  20. How to Use ModelSmart • To Double Truss Members • On Menu, select “Members” / “Double Members” • Click on truss members that you want to double • The truss member number background for doubled members is blue

  21. This Concludes the Lab 4 Lecture

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