1. Anatomy of A Bridge Atin Sinha, Ph.D., P.E. Albany State University Anatomy of A Bridge Atin Sinha, Ph.D., P.E. Albany State University

2. Different Types of Bridges  Truss Bridge  Suspension Bridge  Cable Stayed Bridge

3. Truss Bridge

5. Suspension Bridge

7. Cable Stayed Bridge

9. Loads Experienced by A Bridge  Static (Structural)  Variable (Vehicular Traffic, Pedestrian)  Environmental (Wind, Earthquake)

10. Forces that Act on Bridges Forces that Act on Bridges  Tension  Compression  Torsion  Shear

11. Suspension vs. Cable Stayed

12. Common Trusses Used in Engineering: WarrenPratt HoweK Truss

13. Red represents tension, blue represents compression, and green is no load Now examine the same Warren truss, but with added vertical members

14. Model Bridge Building Steps  Learn the Rules of the Competition  Design the Bridge  Get the Supplies  Build the Bridge  Test the Bridge  Analyze the Failure  Improve Your Design

15. Southwest Georgia Regional Model Bridge Building Contest Design Specifications for the Model Bridge Span 22 in. Maximum Allowable Weight 28.3 g Maximum Allowable Height (Overall) 10 in 10 in Max Superstructure Height 6 in 6 in Max Substructure Height 4 in Minimum vertical clearance through the bridge 2 in Minimum horizontal clearance through the bridge 2 in No height restriction for Middle Schools

16. Design the Bridge  Center the design around the loading point Provide extra bracing around the loading point Provide extra bracing around the loading point  Choose a truss Warren, Pratt or design your own  Draw the bridge to scale on graph paper  Create a list of all the pieces  Cut the pieces to exact size  Label and weight every piece  Allow 10% weight for glue  If you exceed the weight limit, modify the design

17. Preparation for Building the Bridge  Get the wood Hobby stores Hobby stores Specialized Balsa.com Specialized Balsa.com Specialized Balsa.com Specialized Balsa.com Pick out the “good” wood Pick out the “good” wood  Tools Glue Glue Saw/Exacto knife Saw/Exacto knife Gram scale Gram scale Clamps/clothespins Clamps/clothespins Foam Board (optional) Foam Board (optional)  Workspace Good lighting Good lighting Good ventilation Good ventilation

18. Build the Bridge  Tape the top and bottom beams to the design on the graph paper  Glue the remaining pieces and cure overnight holding firmly using pins.  After both trusses are completed, tape them to two fixed boxes spaced correctly apart  Glue bracing on top and bottom  Make sure the bridge is not leaning on one side  Weigh the bridge and record including the specs

19. Test the Bridge  Test before competition if: You have time to build another bridge You have time to build another bridge You are only testing your bridge to a certain point You are only testing your bridge to a certain point  Testing equipment Bathroom scale (top loaded only) Bathroom scale (top loaded only) Bucket and sand (top or bottom) Bucket and sand (top or bottom)  Testing procedure Pour the sand slowly but steadily Pour the sand slowly but steadily Watch for deflection ( 2” is considered failure) Watch for deflection ( 2” is considered failure)

20. Evaluation of the Bridge  Efficiency = mass that bridge held divided by mass of bridge In order to win typically score need to be well above 250 In order to win typically score need to be well above 250  What failed ( Broken member / joints unglued) ? Video taping Video taping Careful examination of broken pieces Careful examination of broken pieces  Improving Design (Add a piece where it failed) Design (Add a piece where it failed) Construction (add notched joint / gusset plate) Construction (add notched joint / gusset plate)

21. Winners From the Past Years Year Bridge Weight (gm) Breaking Load (gm) Structural Efficiency 200328.110276365.7 200425.65789226.1 200522.810197447 200617.59488542 200723.713253559 200828.111114396 200922.75930261