© 2006 Baylor University EGR 1301 Slide 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: 1.Select “Slide Show” with the menu: Slide Show|View Show (F5 key), and hit “Enter” 2.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” 3.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”.

© 2006 Baylor University EGR 1301 Slide 2 Introduction Dr. Carolyn Skurla Speaking

© 2006 Baylor University EGR 1301 Slide 3 F Notes on Tensile Strength F t w Tensile Strength –Material property –Measure cross- sectional area –Load to failure in tension –Calculate tensile strength

© 2006 Baylor University EGR 1301 Slide 4 Notes on Compressive Strength Long, thin members –Buckling will occur –Member fails in bending instead of in compression

© 2006 Baylor University EGR 1301 Slide 5 Notes on Shear Strength of Glue Standard method for testing adhesive strength –Shear the glue joint x y F F

© 2006 Baylor University EGR 1301 Slide 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.

© 2006 Baylor University EGR 1301 Slide 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.

© 2006 Baylor University EGR 1301 Slide 8 How to Use ModelSmart Select Size/Grade of Wood –On Menu, select “Members” / “Default Material Type” / “Balsa Wood” / “1/4” Balsa – BAL8D3”

© 2006 Baylor University EGR 1301 Slide 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.

© 2006 Baylor University EGR 1301 Slide 10 How to Use ModelSmart Add Members –Construct your truss bridge by adding all the truss members.

© 2006 Baylor University EGR 1301 Slide 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.

© 2006 Baylor University EGR 1301 Slide 12 How to Use ModelSmart Add Loads –On Menu, select “Loads” and select “Vertical Down.” –The cursor will change to a down-pointing arrow.

© 2006 Baylor University EGR 1301 Slide 13 How to Use ModelSmart Add Loads –Place a “Vertical Down” load on the joints at each end of the top horizontal member.

© 2006 Baylor University EGR 1301 Slide 14 How to Use ModelSmart Analyze your truss. –On Menu, select “Analysis” / “Analysis Options”. –Select “Show Displacements”, “Show Broken Members”, and “Show Stress Levels.”

© 2006 Baylor University EGR 1301 Slide 15 How to Use ModelSmart Understanding analysis results –Red  Broken –Blue  Compression –Green  Tension

© 2006 Baylor University EGR 1301 Slide 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.

© 2006 Baylor University EGR 1301 Slide 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.

© 2006 Baylor University EGR 1301 Slide 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”

© 2006 Baylor University EGR 1301 Slide 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

© 2006 Baylor University EGR 1301 Slide 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

© 2006 Baylor University EGR 1301 Slide 21 This Concludes the Lab 4 Lecture