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Truss Design Project

Truss Design Project. Kevin LaBeau Thao Lai EGR 209 Dr. Reffeor October 27, 2003. Problem Statement. Apply Math and Science skills to: Create a 24m bridge in West Point Bridge Designer (WPBD) Costs around $1500-$2500 Compute tensile and compressive strengths

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Truss Design Project

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  1. Truss Design Project Kevin LaBeau Thao Lai EGR 209 Dr. Reffeor October 27, 2003

  2. Problem Statement • Apply Math and Science skills to: • Create a 24m bridge in West Point Bridge Designer (WPBD) • Costs around $1500-$2500 • Compute tensile and compressive strengths • Calculate internal forces for the bridge • Calculate the factors of safety • Find a standard hex bolt to withstand the forces

  3. Final Truss Bridge Design Results and Analysis • Bridge Cost: $2169.51

  4. Tensile and Compressive Strengths • Strengths related to • Material – High-Strength Low-Alloy Steel • Size of member • Solid Bars Vs. Hollow Tubes

  5. Tensile and Compressive Strengths

  6. Self-weight of truss members W = γs Am L where, γs= the density of the material Am= the cross-sectional area of the member L = the length of the member

  7. Self-Weight of Members

  8. Self weight on any joint • Total factored dead load on any joint Load factor = 1.25 for self weight given by WPBD

  9. Sample Calculations for Joint A Member identification

  10. Dead load diagram

  11. Situation 1 • Live load over Joint B.

  12. Situation 2 • Live load over Joint C.

  13. Situation 3 • Live load over Joint D.

  14. Member Forces • (T): Tension (C): Compression• All forces in kN

  15. Strength Force • Factor of Safety = Structural Adequacy • Average Factor of Safety • 4.122

  16. Bolt Size • Bolt grade = 10.9 • Tensile strength = 1040 MPa • Shear stress = .5*tensile strength • 520MPa • minimum bolt diameter = 55mm • standard bolt diameter = 56mm where, V = the shear force A = the cross-sectional area of the bolt

  17. Bridge Costs (minus cost of bolts)

  18. F F Ffelt Ffelt Ffelt Ffelt Discussion Geometric Stability • Triangle: most stable truss formation • evenly distributes forces through members • vertical forces unevenly distributed on the square. • squares can also pivot and collapse

  19. Geometric Stability • Arches • High resistance to the forces that will put stress on the bridge • The force will act in the direction of the member and on the joint itself • Stronger bridge structure = smaller members = lower costs

  20. Conclusion • Designs based on mathematical and physical concepts • Triangles are stronger than squares. • Arches evenly distribute forces for more stability. • Real life issues: costs & materials account for the design process • Important to keep costs at a minimum, but essential to never compromise safety • Engineers apply physical and mathematical models to design and build projects suitable for lives to use. • While working on this project, Kevin understands why SHEER STRESS = Thao

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