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

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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

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

  3. 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 Beam Deflection

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

  5. 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 To Increase the Moment of Inertia

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

  8. Compression, Tension, and Torsion

  9. 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) Stress and Strain of Different Materials

  10. 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 Design Optimization

  11. 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 Summary

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