Steel Design BCN 3431

Steel Design BCN 3431

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

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