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Fundamentals for the Up-and-Coming Bridge Engineer

Fundamentals for the Up-and-Coming Bridge Engineer. Forces on Beams and Material Properties. OSU College of Engineering Summer Institute - Robotics. Outline. Beam Strength and Deflection Moment of Inertia Types of Forces Applied Young’s Modulus (stress and strain) Optimization.

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Fundamentals for the Up-and-Coming Bridge Engineer

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  1. Fundamentals for theUp-and-Coming Bridge Engineer Forces on Beams and Material Properties OSU College of Engineering Summer Institute - Robotics

  2. Outline • Beam Strength and Deflection • Moment of Inertia • Types of Forces Applied • Young’s Modulus (stress and strain) • Optimization

  3. Beam Deflection • Every object acts as a spring – it will deflect when a force is applied • Extent of deflection depends on force applied, material properties and object shape

  4. I = Area Moments of Inertia (depends on object shape) h b Moments of Inertia • A measure of resistance to deflection • A larger moment of inertia means that the beam will be more resistant to deflection

  5. To Increase the Moment of Inertia • Increase the size: • But as you increase the size, you increase the weight and cost • Change the cross-sectional shape: • A hollow cross-section is stronger for the amount of material used

  6. The beams have the same cross-sectional area, but the shapes and moments of inertia are different With the same volume of material, the hollow beam is stronger (higher moment of inertia). Differences in Deflection

  7. Types of Forces on a Bending Beam Top of beam – under tension Bottom of beam – under compression

  8. Compression, Tension, and Torsion Reference: http://www.diydoctor.org.uk

  9. Stress and Strain of Different Materials Different materials have different strain responses to the same stress. Choose a material that suits your needs Stress vs. Strain Curves: Linear Portion (Hooke’s Law): Young’sModulus (slope of curve or material stiffness)

  10. Design Optimization • Engineering is not about building the strongest possible bridge • Engineering is about building a bridge that is strong enough and balances cost, strength, time required to build, etc • Engineering is about trade-offs and meeting design specifications

  11. Summary • Beam strength depends on force applied, material properties and object shape • Important material properties include moment of inertia and Young’s Modulus (stress and strain) • Three types of forces are compression, tension, and torsion • These concepts will be helpful in the West Point Bridge Designer

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