ENCE 710 Design of Steel Structures IV. COMPOSITE STEELCONCRET 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 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) 2 Composite Action 3 Effective Width AISC-I3 1. 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) 4 Nominal Moment Strength Nominal Moment Strength of Fully Composite Section (AISC 14th Edition Art. I3.2a) 1.
hc / t w p 3.76 / E F yf Mn = based on plastic stress distribution on the Composite Section; b = 0.9 2. hc / t w p 3.76 / E
F yf Mn = based on superposition of elastic stresses, considering the effect of shoring; = 0.9 5 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)
6 Shear Connectors 7 Shear Variation V = Cmax = 0.85fcbEts V = Tmax =AsFy N = Cmax/Qn or Tmax/Qn Whichever is smaller 8 Nominal Strength Qn
Qn = 1. Headed Steel Stud (AISC Eq. I8-1) Qn 0.5 Aw 2. Connectors 2) f c ' E c Rg R p Asc Fu Channel
(AISC Eq. I8- Qn 0.3(t f 0.5t w ) Lc f c ' Ec 9 Nominal Strength Qn 10 Connector Design Fatigue Strength nZ r I 6.10.7.4.1b-1)
Vsr Q (AASHTO LRFD Eq. Zr = d 1) (AASHTO LRFD Eq. 6.10.7.4.2- p 2 5.5 d 2/2; where = 34.5 4.28 log N (AASHTO LRFD Eq. 6.10.7.4.22)
Exampl e: 11 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.) 12 Composite Column Section (rolled steel shape encased in
concrete) Using Effective Section Properties (I2-4, 5 & 6) P0 As Fy Asr Fyr 0.85 Ac f ' c Pe1 2 EI eff K1 L 2 EI eff E s I s 0.5 E s I se C1 E c I c 13 Filled Composite Column Example
AISC I2-2b (a)Compact (b)Noncompa ct (c)Slender 14 Filled Composite Column Example For compact sections Ac = bfhf+(r-t)r-t)2+2bf(r-t)r-t)+2hf(r-t)r-t) Ac = (r-t)8.5 in.)(r-t)4.5 in.) + (r-t)0.375 in.)2 + (r-t)8.5 in.)(r-t)0.375 in.) +
2(r-t)4.5 in.)(r-t)0.375 in.) = 48.4 in.2 b1h12 2(b2 )(h22 ) 8 (r t ) 2 h2 4(r t ) 2 Ic 2(r t )( ) 2( )( ) 111in.4 12 12 8 9 2 2
3 P0 As Fy Asr Fyr 0.85 Ac f ' c P0 = (r-t)10.4 in.2)(r-t)46ksi) + 0.85(r-t)48.4 in.2)(r-t)5 ksi) = 684kips EI eff E s I s 0.5 Es I se C 3 Ec I c EIeff = (r-t)29,000 kis)(r-t)61.8 in.4) + (r-t)0.90)(r-t)3,900 ksi)(r-t)111 in.4) = 2,180,000 kip-in.2 15 Filled Composite Column Example Pe1 2 EI eff
K1 L 2 Pe = 2(r-t)2,180,000 kip-in.2)/(r-t)1.0(r-t)14 ft)(r-t)12 in./ft))2 = 762 kips kips = 0.898 2.25 P0/Pe = 684 kips/762 p0 / Pe 0.898 Pn P0 0.658 (684kips) 0.658 470kips
cPn = 0.75(r-t)470 kips) = 353 kips > 336 kips o.k. 16