1Developed by Scott CivjanUniversity of Massachusetts, Amherst
Chapter I:
Composite Member Design
Composite Beam - AISC Manual 14th Ed 2
Slab effective width, be
Section I3.1aTo each side of the beam, be is limited by:
one-eighth beam spanone-half distance to adjacent beamdistance to edge of slab
Composite Beam - AISC Manual 14th Ed
distance to edge of slab
Lowest value controls.
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Metal Deck Slab Section I3.2c
tc 2
hr 3
1.5
0.5
Composite Beam - AISC Manual 14th Ed
wr 2
4
wr = average deck widthhr = height of decktc = thickness of concrete above the deck
steel beam
Fully Composite Beam: Bending Strength
Composite Beam - AISC Manual 14th Ed
Bending Strength
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b = 0.90 (b = 1.67)
Bending Strength
Composite Beam - AISC Manual 14th Ed 6
POSITIVE MOMENT
For h/tw
The strength is determined as the plastic stress distribution of the composite section.(*Note: All current ASTM A6 W, S and HP shapes satisfy this limit.)
yFE
.763
Bending Strength
Composite Beam - AISC Manual 14th Ed
(*Note: All current ASTM A6 W, S and HP shapes satisfy this limit.)
NEGATIVE MOMENT
It is typically assumed that the concrete carries no tensile forces and reinforcement is minimal, therefore strength is identical to a bare steel section.
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INSERT INFORMATION: STRENGTH OF FULLY COMPOSITE BEAM SECTION CALCULATIONS
Handout on Calculations:
Composite Beam - AISC Manual 14th Ed
Handout on Calculations: FullyCompositeCalcs.PDF
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Fully Composite Strength can be determined by using Table 3-19.
Y2 - Calculated per handout
Bending Strength
Composite Beam - AISC Manual 14th Ed
Y1 = 0 if PNA in the slab,Calculated per handout if PNA in the beam flange or web.
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Table 3-19 Nomenclature(page 3-14)
be
a
a/2 Location of effective concrete flange force (Qn)
4
E
q
.
s
p
a
c
e
s
12345
TFL
BFL
tf
Beam Flange Enlarged Detail
Composite Beam - AISC Manual 14th Ed
aYcon Y2 TFL(pt.1)BFL(pt.5)
67 Y1 = Distance from top of steel
flange to any of the seven tabulated PNA locations
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15
To reach fully composite strength,shear studs must transfer Qn for Y1 = 0 (maximum value) listed in Table 3-19.
This is equivalent to value C* in calculations (handout).
Bending Strength
Composite Beam - AISC Manual 14th Ed
This is equivalent to value C* in calculations (handout).
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Shear Stud Strength
Composite Beam - AISC Manual 14th Ed 12
Strength of each stud, QnEquation I8-10 5n sa c c g p sc uQ . A f 'E R R A F=
limits value to crushing of concrete around the shear stud.
ccsc 'EfA.50
Composite Beam - AISC Manual 14th Ed
limits value to strength of individual shear studs.
concrete around the shear stud.
uscpg FARR
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Asa = cross sectional area of shear studEc = modulus of elasticity of concreteFu = shear stud minimum tensile strength
(typically 65ksi)Rg accounts for number of studs welded in each deck rib and wr/hr.
uscpgccscn FARR'EfA.Q = 50
Composite Beam - AISC Manual 14th Ed
Rg accounts for number of studs welded in each deck rib and wr/hr.Values are 1.0, 0.85 or 0.7.
Rp accounts for deck rib orientation with respect to the beam, stud engagement in the concrete above the rib, and weak or strong stud location.Values are 0.75 or 0.6.
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Strength, Qn, for one shear studTable 3-21
Composite Beam - AISC Manual 14th Ed 15
Limitations on shear stud placementfor shear studs placed in metal decking:
Section I8.2dCenter-Center Spacing: > 4 times Diameter
8 times slab thickness 36 inches
Composite Beam - AISC Manual 14th Ed
36 inches
Section I3.2c and I8.1Shear Stud Diameter: 3/4
2.5 times flange thickness unless over web
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Composite strength requires that shear studs transfer Qn to each side of the maximum moment in the span.
Composite Beam - AISC Manual 14th Ed
If Qn strength of the shear studs is inadequate to provide fully composite action, the beam is partially composite.
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Partially Composite Beam: Bending Strength
Composite Beam - AISC Manual 14th Ed
b = 0.90 (b = 1.67)
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INSERT INFORMATION: STRENGTH OF PARTIALLY COMPOSITE BEAM SECTION CALCULATIONS
Handout on Calculations:
Composite Beam - AISC Manual 14th Ed
Handout on Calculations: PartiallyCompositeCalcs.PDF
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Partially Composite Strength can be determined by using Table 3-19.
Y2 - Calculated per handout
Composite Beam - AISC Manual 14th Ed
Y1 - Calculated per handout
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Partially Composite Action is limited by the total strength of shear studs.
Qn listed in Table 3-19.
This is equivalent to value C* in calculations (handout).
Composite Beam - AISC Manual 14th Ed
This is equivalent to value C* in calculations (handout).
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Composite Beam: Shear Strength
Composite Beam - AISC Manual 14th Ed 22
SHEAR STRENGTH
It typically is assumed that the slab carries no shear forces. Therefore, strength is identical to a bare steel section.
Composite Beam - AISC Manual 14th Ed 23
Composite Beam Deflection Calculations
Composite Beam - AISC Manual 14th Ed
Deflection Calculations
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Deflection CalculationsFully Composite
Itr = transformed section moment of inertia
Lower bound values of Itr are found in Table 3-20 (ILB).
Composite Beam - AISC Manual 14th Ed
Lower bound values of Itr are found in Table 3-20 (ILB).Values assume concrete area equal to Qn/Fy rather than actual area.
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Deflection Calculations Partially Composite
Equation C-I3-4( )strf
nsequiv IIC
QII +=
Composite Beam - AISC Manual 14th Ed
Iequiv = effective moment of inertiaIs = moment of inertia of steel section onlyItr = fully composite moment of inertiaSQn = partially composite shear transferCf = fully composite shear transfer
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Deflection Calculations Partially Composite
Equation C-I3-5( )strf
nseff SSC
QSS +=
Composite Beam - AISC Manual 14th Ed
Seff = effective elastic section modulusSs = elastic section modulus of steel section onlyStr = fully composite elastic section modulusQn = partially composite shear transferCf = fully composite shear transfer
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Deflection Calculations Partially Composite
Table 3-20 can be used for
Composite Beam - AISC Manual 14th Ed
Table 3-20 can be used for lower bound values of Iequiv.
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