ENCE 710 Design of Steel Structures

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)

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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
Fb 0.9 2. Mn based on
superposition of elastic stresses,
considering the effect of shoring Fb
0.9
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Plastic Stress Distribution
Case 1 (if a ts) S J Eq. (16.7.1 to 5) Case
2 (if a gt ts) S J Eq. (16.7.6 to 10)
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Shear Connectors
8
Shear Variation
V Cmax 0.85fcbEts
V Tmax AsFy
N Cmax/Qn or Tmax/Qn Whichever is smaller
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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
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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.)
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Composite Column Section (rolled steel shape
encased in concrete)
Using Effective Section Properties (I2-4, 5 6)
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Filled Composite Column Example

• AISC I2-2b
• Compact
• Noncompact
• Slender

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Filled Composite Column Example

• For compact sections
• Ac bfhfp(r-t)22bf(r-t)2hf(r-t)
• Ac (8.5 in.)(4.5 in.) p(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

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Filled Composite Column Example

• Pe p2(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
• fcPn 0.75(470 kips) 353 kips gt 336 kips
  o.k.