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ENCE 710 Design of Steel Structures

ENCE 710 Design of Steel Structures. IV. COMPOSITE STEEL-CONCRET CONSTRUCTION C. C. Fu, Ph.D., P.E. Civil and Environmental Engineering Department University of Maryland. Introduction. Following subjects are covered: Composite Action Effective Width Nominal Moment Strength

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ENCE 710 Design of Steel Structures

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  1. ENCE 710 Design of Steel Structures IV. COMPOSITE STEEL-CONCRET CONSTRUCTION C. C. Fu, Ph.D., P.E. Civil and Environmental Engineering Department University of Maryland

  2. Introduction Following subjects are covered: • Composite Action • Effective Width • Nominal Moment Strength • Shear Connectors, Strength and Fatigue • Formed Steel Deck Reading: • Chapters 16 of Salmon & Johnson • AISC LRFD Specification Chapters B (Design Requirements) and I (Design of Composite Members)

  3. Composite Action

  4. Effective Width • AISC-I3 • Interior • BE ≤ L/4 • BE ≤ b0 (for equal beam spacing) • 2. Exterior • BE ≤ L/8 + (dist from beam center to edge of slab • BE ≤ b0/2 + (dist from beam center to edge of slab)

  5. Nominal Moment Strength • Nominal Moment Strength of Fully Composite Section • (AISC 14th Edition Art. I3.2a) • 1. • Mn = based on plastic stress distribution • on the Composite Section; • Φb = 0.9 • 2. • Mn = based on superposition of elastic • stresses, considering the effect of shoring; • Φb = 0.9

  6. Plastic Stress Distribution Case 1 (if a ≤ ts): S & J Eq. (16.7.1 to 5) Case 2 (if a > ts): S & J Eq. (16.7.6 to 10)

  7. Shear Connectors

  8. Shear Variation V’ = Cmax = 0.85fc’bEts V’ = Tmax =AsFy N = Cmax/Qn or Tmax/Qn Whichever is smaller

  9. Nominal Strength Qn Qn = 1. Headed Steel Stud (AISC Eq. I8-1) 2. Channel Connectors (AISC Eq. I8-2)

  10. Nominal Strength Qn

  11. Connector Design – Fatigue Strength (AASHTO LRFD Eq. 6.10.7.4.1b-1) Zr = d 2 5.5 d 2/2; (AASHTO LRFD Eq. 6.10.7.4.2-1) where  = 34.5 – 4.28 log N (AASHTO LRFD Eq. 6.10.7.4.2-2) Example:

  12. Composite Column Section (rolled steel shape encased in concrete) AISC I2.1. Encased Composite Columns AISC I2.2. Filled Composite Columns (Ref: Separate handout with examples.)

  13. Composite Column Section (rolled steel shape encased in concrete) Using Effective Section Properties (I2-4, 5 & 6)

  14. Filled Composite Column Example • AISC I2-2b • Compact • Noncompact • Slender

  15. Filled Composite Column Example • For compact sections • Ac = bfhf+π(r-t)2+2bf(r-t)+2hf(r-t) • Ac = (8.5 in.)(4.5 in.) + π(0.375 in.)2 + (8.5 in.)(0.375 in.)+ 2(4.5 in.)(0.375 in.) = 48.4 in.2 • P0 = (10.4 in.2)(46ksi) + 0.85(48.4 in.2)(5 ksi) = 684kips • EIeff = (29,000 kis)(61.8 in.4) + (0.90)(3,900 ksi)(111 in.4) • = 2,180,000 kip-in.2

  16. Filled Composite Column Example • Pe = π2(2,180,000 kip-in.2)/(1.0(14 ft)(12 in./ft))2 = 762 kips • P0/Pe = 684 kips/762 kips = 0.898 ≤ 2.25 • φcPn = 0.75(470 kips) = 353 kips > 336 kips o.k.

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