04 - design of steel flexural members

7/27/2019 04 - Design of Steel Flexural Members

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Design of Steel Flexural Members

Design for :

Economy choose lightest beam that can

carry the load

Serviceability May need deeper beam to

prevent serviceability problems such asdeflection or vibrations


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Design of Steel Flexural Members

Bending about strong

axis (x-axis):

Bending about weak

axis

X X

w

Y Y

w


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Stress and Strain in the Cross-section

Strain

Stress

N.A.

small =y plastic

E = F/ E F/

N.A.

small =y plastic

N.A.

small F Fy Fy Fy


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LRFD Equation

nii RQ

nu MM

Load Effect Factored Resistance


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Specification for Flexural Members

p. 16.1-207


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Part 5 Design of Flexural Members

Beam Tables Table 5-3, p. 5-42 5-48

Beam Charts Table 5-5, p. 5-71 5-102

Beam Diagrams Table 5-17, p. 5-162 5-177


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Flexural Design Example p. 27 notes

You are to select the lightest A992 steel

beam that can carry a live load of 1.9 k/ft

and a dead load of 1.4 k/ft for a span of 33

feet. Assume first continuous lateralsupport, and then lateral support 10 ft from

each end only.


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Flexural Design Example p. 27 notes

Select an A36 channel to carry a

500 lb/ft live load and a 300 lb/ft

dead load for a simply supportedspan of 15 ft. Lateral support will

be continuous for both flanges.


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Deflections

Serviceability (not strength) Chapter L

Calculated for service live load only

KBC: max = L/360 floor members

max = L/240 roof members

where max = maximum deflection

L = span length


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Deflections

p.5-11 LRFD

Can also be written

xIC

ML

1

2

xIC

ML

L1

12


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Check deflection of beams chosen in

previous examples


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Beam Shear

Maximum moment:

Also an internal shear:

8

2

max

wLM

w

V

M

w

R

2max

wLV


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Beam Shear


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Beam Shear


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Shear Strength of Beams

p. 16.1-35 LRFD (with no holes in web)

if,

where,

Fyw = yield strength web = Fy for steel shapes

Aw = area of web = d x tw

p. 16.1 67 At connection where holes are in web:

wywnv AFV )6.0(9.0yww F

E

t

h45.2

true for steel shapes

nvunn AFRV )6.0(75.0


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Check Shear Strength of beams

previously designed


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Floor Systems for Steel Frame Structures

Typical floor systems consist of steel

decking filled with concrete

Figures of steel decking p. 16.1- 223

(Commentary to chapterI)


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Example

Data Sheet

for Steel Decking


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Construction Details


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Design Example with Floor Systemp. 33 notes

Design the floor system for an office building

using the KBC minimum distributed live

load for corridors (to allow flexibility of

office space). The depth of the floorbeams is limited to 24.5 to allow space for

mechanical systems. Use EC366 steel

decking and lightweight concrete withoutshoring.


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30

45

30

30 30

24.5


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KBC Minimum Distributed Live Loads


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KBC Minimum Concentrated Load


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Composite Construction

Detail of shear connectors


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PNA in steel

PNA in concrete

b

Ycon

b

Ycon

bb

Ycon

a

a

C = Ccon+Cst

Tst

C=T

C con

Tst


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Ccon= 0.85fcbaT = FyAs

C and T can not exceed force carried by studs, Qn

Qn=0.85 fcba

bf

Qac

n

'85.0

Depth of compressionblock


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Composite Construction p.5-33

Y1 Distance from PNA to beam top

flange

Y2 Distance from concrete flange force

to beam top flange

b effective width of concrete slab flange

a effective concrete flange thickness

04 - design of steel flexural members

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