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Structural Engineering

Structural Engineering. Outline. Introduction to Structural Engineering Design Process Forces in Structures Structural Systems Materials Definitions of Important Structural Properties Triangles UNITS (Dimensional Analysis). Structural Engineering. What does a Structural Engineer do?

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Structural Engineering

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  1. Structural Engineering

  2. Outline • Introduction to Structural Engineering • Design Process • Forces in Structures • Structural Systems • Materials • Definitions of Important Structural Properties • Triangles • UNITS (Dimensional Analysis)

  3. Structural Engineering • What does a Structural Engineer do? • A Structural Engineer designs the structural systems and structural elements in buildings, bridges, stadiums, tunnels, and other civil engineering works (bones) • Design: process of determining location, material, and size of structural elements to resist forces acting in a structure

  4. Design Process

  5. Engineering Design Process • Identify the problem (challenge) • Explore alternative solutions • Research past experience • Brainstorm • Preliminary design of most promising solutions • Analyze and design one or more viable solutions • Testing and evaluation of solution • Experimental testing (prototype) or field tests • Peer evaluation • Build solution using available resources (materials, equipment, labor, cost)

  6. Design Process in Structural Engineering • Select material for construction • Determine appropriate structural system for a particular case. Justify (tell me why) you used these particular structural systems. • Determine forces acting on a structure • Calculate size of members and connections to avoid failure (collapse) or excessive deformation

  7. Forces in Structures

  8. Forces Acting in Structures • Force induced by gravity (F=ma) • Dead Loads (permanent): self-weight of structure and attachments • Mass Vs. Weight • Compression, Tension, bending, torsion

  9. Forces Acting in Structures Vertical: Gravity Lateral: Wind, Earthquake

  10. 100 lb Compression Forces in Structural Elements 100 lb Tension

  11. 100 lb Bending Forces in Structural Elements Torsion

  12. Structural Systems

  13. Arch Typical Structural Systems

  14. C T C C T Forces in Truss Members Typical Structural Systems Truss

  15. Frame Typical Structural Systems

  16. Typical Structural Systems Flat Plate

  17. Typical Structural Systems Folded Plate

  18. Typical Structural Systems Shells

  19. Racking Failure of Pinned Frame Infilled Frame Rigid Joints Braced Frame Providing Stability for Lateral Loads

  20. Materials Used in Civil Engineering Metals • Cast Iron • Steel • Aluminum • Concrete • Wood • Fiber-Reinforced Plastics

  21. Engineering Properties of Materials • Steel • Maximum stress: 40,000 – 120,000 lb/in2 • Maximum strain: 0.2 – 0.4 • Modulus of elasticity: 29,000,000 lb/in2 • Concrete • Maximum stress: 4,000 – 12,000 lb/in2 • Maximum strain: 0.004 • Modulus of elasticity: 3,600,000 – 6,200,000 lb/in2 • Wood Values depend on wood grade. Below are some samples • Tension stress: 1300 lb/in2 • Compression stress: 1500 lb/in2 • Modulus of elasticity: 1,600,000 lb/in2

  22. Concrete Components • Sand (Fine Aggregate) • Gravel (Coarse Aggregate) • Cement (Binder) • Water • Air

  23. Fiber-Reinforced Composites Composite Laminate Polyester Polymer Matrix Epoxy Vinylester Glass • Functions of matrix: • Force transfer to fibers • Compressive strength • Chemical protection Fiber Materials Aramid (Kevlar) Carbon • Function of fibers: • Provide stiffness • Tensile strength

  24. Properties of Materials(Why are they used)

  25. T Example (English Units): T = 1,000 lb (1 kip) A = 10 in2. Stress = 1,000/10 = 100 lb/in2 Stress = Force/Area Section X Example (SI Units): 1 lb = 4.448 N (Newton) 1 in = 25.4 mm T = 1,000 lb x 4.448 N/lb = 4448 N A = 10 in2 x (25.4 mm)2 = 6450 mm2 (1 in)2 Stress = 4448/6450 = 0.69 N/mm2 (MPa) Section X T T Definition of Stress

  26. T DL Lo T Definition of Strain Strain = DL / Lo Example: Lo = 10 in. DL = 0.12 in. Strain = 0.12 / 10 = 0.012 in./in. Strain is dimensionless!! (same in English or SI units)

  27. Compressive Failure Tensile Failure Engineering Properties of Structural Elements • Strength • Ability to withstand a given stress without failure • Depends on type of material and type of force (tension or compression)

  28. Engineering Properties of Structural Elements • Stiffness (Rigidity) • Property related to deformation • Stiffer structural elements deform less under the same applied load • Stiffness depends on type of material (E), structural shape, and structural configuration • Two main types • Axial stiffness • Bending stiffness

  29. T DL Lo T Axial Stiffness Stiffness = T / DL Example: T = 100 lb DL = 0.12 in. Stiffness = 100 lb / 0.12 in. = 833 lb/in.

  30. Bending Stiffness Displacement Force Stiffness = Force / Displacement Example: Force = 1,000 lb Displacement = 0.5 in. Stiffness = 1,000 lb / 0.5 in. = 2,000 lb/in.

  31. Stiffest Stiffness of Different Structural Shapes Stiff Stiffer

  32. Types of Structural Elements – Bars and Cables Bars can carry either tension or compression Cables can only carry tension

  33. Loads Compression Tension Types of Structural Elements – Beams

  34. Triangles

  35. Formulas • SOH, CAH, TOA • c2 = a2 + b2 H O A

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