ADVANCEDBeam_ManualComposite

1Developed by Scott CivjanUniversity of Massachusetts, Amherst

Composite Beam - AISC Manual 14th Ed

Chapter I: Composite Member Design

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

Lowest value controls.

3


Metal Deck Slab Section I3.2c

wr 2

tc 2

hr 3

4

1.5

0.5

wr = average deck widthhr = height of decktc = thickness of concrete above the deck

steel beam


Fully Composite Beam: Bending Strength

5


b = 0.90 (b = 1.67)

6

Bending Strength


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

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.

7

Bending Strength


INSERT INFORMATION: STRENGTH OF FULLY COMPOSITE BEAM SECTION CALCULATIONS

Handout on Calculations: FullyCompositeCalcs.PDF

8


Fully Composite Strength can be determined by using Table 3-19.

Y2 - Calculated per handout

Y1 = 0 if PNA in the slab,Calculated per handout if PNA in the beam flange or web.

9

Bending Strength


Table 3-19 Nomenclature(page 3-14)

be

aYcon

a/2

Y2

Location of effective concrete flange force (Qn)

TFL(pt.1)BFL(pt.5)

67 Y1 = Distance from top of steel

flange to any of the seven tabulated PNA locations

4

E

q

.

s

p

a

c

e

s

12345

TFL

BFL

tf

10

Beam Flange Enlarged Detail

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).

11

Bending Strength


Shear Stud Strength

12


limits value to strength of individual shear studs.

Strength of each stud, Qn

Equation 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

uscpg FARR

13


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.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.

14

uscpgccscn FARR'EfA.Q 50


Strength, Qn, for one shear studTable 3-21

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

Section I3.2c and I8.1Shear Stud Diameter: 3/4

2.5 times flange thickness unless over web

16


Composite strength requires that shear studs transfer Qn to each side of the maximum moment in the span.

If Qn strength of the shear studs is inadequate to provide fully composite action, the beam is partially composite.

17


Partially Composite Beam: Bending Strength

b = 0.90 (b = 1.67)

18


INSERT INFORMATION: STRENGTH OF PARTIALLY COMPOSITE BEAM SECTION CALCULATIONS

Handout on Calculations: PartiallyCompositeCalcs.PDF

19


Partially Composite Strength can be determined by using Table 3-19.


20



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).

21


Composite Beam: Shear Strength

22


SHEAR STRENGTH

It typically is assumed that the slab carries no shear forces. Therefore, strength is identical to a bare steel section.

23


Composite Beam Deflection Calculations

24


Deflection CalculationsFully Composite

Itr = transformed section moment of inertia

Lower bound values of Itr are found in Table 3-20 (ILB).Values assume concrete area equal to Qn/Fy rather than actual area.

25


Deflection Calculations Partially Composite

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

26

Equation C-I3-4 strf

nsequiv IIC

QII



Equation C-I3-5 strf

nseff SSC

QSS

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

27



Table 3-20 can be used for lower bound values of Iequiv.

28

Date post:	14-Oct-2015
Category:	Documents
Upload:	saleem-malik
View:	10 times
Download:	0 times

ADVANCEDBeam_ManualComposite

Documents