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

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