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Compression Members

Compression Members. Compression Members. Compression Members. Compression Members. Stress:. Uniform over entire cross section. Compression Members. Compression Members: Structural elements subjected only to axial compressive forces.

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Compression Members

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  1. Compression Members

  2. Compression Members

  3. Compression Members

  4. Compression Members

  5. Stress: Uniform over entire cross section Compression Members Compression Members: Structural elements subjected only to axial compressive forces Loads are applied along a longitudinal axis through the centroid In reality: (a) Secondary Bending due to Load Eccentricities - Ignore (b) Computed Bending Moment - Treat as Beam Column

  6. Types of Compression Members Columns Vertical Members that support vertical loads Trusses and Bracing Systems Compressive Forces Struts Smaller compression members not classified as columns

  7. Compression Members • Compression members are susceptible to BUCKLING • BUCKLING – Loss of stability • Axial loads cause lateral deformations (bending-like deformations) P is applied slowly P increases Member becomes unstable - buckles

  8. Column Theory Axial force that causes Buckling is called Critical Load and is associated to the column strength • Pcr depends on • Length of member • Material Properties • Section Properties

  9. Let’s Have Some Fun

  10. Column Theory - Euler Buckling

  11. Elastic Buckling Column Theory - Euler Buckling

  12. Compression Members – Stress-Strain Behavior Tension Test Data

  13. Compression Members – Stress-Strain Behavior Coupon tests different than short column tests

  14. Compression Members – Stress-Strain Behavior Rolled Shapes

  15. Compression Members – Stress-Strain Behavior Rolled Shapes Tips of flanges and web cool down first and shorten Hot liquid areas follow

  16. Compression Members – Stress-Strain Behavior Rolled Shapes Tips of flanges and web have solidified Hot liquid areas cool down and shorten further Solidified flanges resist shortening Residual Compressive stresses in flanges Residual tensile stresses in remaining Residual stresses 10-15 ksi

  17. Compression Members – Stress-Strain Behavior

  18. Column Strength Consider a Long Slender Column Material Behavior ELASTIC BUCKLING

  19. Column Strength Consider a Shorter Column Material Behavior INELASTIC BUCKLING

  20. Column Theory - Very Short Columns Consider a Very Short Column PLASTIC BEHAVIOR Yielding takes place before any instabilities

  21. Column Theory - Column Strength Curve

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