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

5

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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