Tutorial 1- Properties and Section Classification

8/12/2019 Tutorial 1- Properties and Section Classification

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Tutorial 1

June 4 2013

Properties

Section Classification


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EXAMPLE 1Determine the shape factor for the I-section :

610 x 229 x 125 UB S 275

Section properties can be readily obtained from

tables for Universal beams (refer tables)

Wel,yy = 3220 cm3 Wpl,yy= 3680 cm3 Shape factor = Wpl,yy / Wel,yy= 3680/3220= 1.143 The value of shape factor for most I sections is

about 1.15

SECTIONS CLASSIFICATIONClassification of Steel Cross Sections is Based on :Eurocode 1993- 1-1 : Table 3.1 , Clause 5.5 and Table 5.2


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EXAMPLE 2 A rectangular section shown.

Assumefy=275 N/mm2. Find the following:

20 mm

150 mm


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Elastic section modulusWel= bd2/6= 20 x 1502/6 =75000mm3

Elastic Moment capacityMe = Welx = 75000 x 275 =20625000Nmm = 20.6kNm Plastic section modulus

Wpl = bd2/4=112500mm3 Plastic Moment capacity

Mp = Wplx = 112500 x 275 = 30937500 Nmm= 30.94kNm. Shape factor for section

Shape factor = Wpl / Wel= 112500/75000=1.5


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EXAMPLE 3Section 610 x 229 x 125 UB S 275 subject to pure bending

Section properties can be taken from published tables tf=19.6 mm tw = 11.9 mm B=229 mm r=12.7 mm

Table 3.1 : since tw=11.9 mm fyw=275 N/mm2

Since tf =19.6 mm fyf= 275 N/mm2

Therefore fyis taken as 275 N/mm2 ; the lower value

c = 229/211.9/212.7= 95.85

c/tf=95.85/19.6=4.89 d/tw= 46.0

Since the section is symmetrical about the major axis i.e the axis ofbending and consequently the neutral axis is atmid-height

92.0275

235

f

235 5.05.0

y

For flange;

For web; =0.92


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Outstand

compression

element

Actual

c/tf = 4.89 =0.92

Limits

9=9x0.92=8.28

10=10x0.92=9.214=14x0.92=12.88

Flange

outstand is

plastic orclass 1

Web

Since purebending;

neutral axis is

at mid depth

Actual

d/tw =46=0.92

Limits

72=72x0.92=66.2483=83x0.92=76.36

124=124x0.92=114.1

Since

d/t


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The cross section is plastic since all elements are

plastic

Note: if one element is having a different classification;then the section will take the lower one

Example: if flange is compact and web plastic ; thensection will be compact

Example: if flange is semi-compact and web plastic;then section is semi-compact


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EXAMPLE 4Section 610x229x125 UB S275 under pure compression load of

3200 kN

Section Properties: Take from tables

Design strength Py:

tw=11.9 mm therefore fyw=275 N/mm2using table 3.1

tf =19.6 mm Therefore fyf=275 N/mm2using table 3.1

Classifying flange

92.0275235

f235

5.05.0

yf

c/tf = 4.89

Since B/T


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Classifying the web

The limiting value of d/t is 33, 38 and 42 Actual d/t=46.0 Therefore the web is Slender

The section takes the lowest classification for flange andweb So the section is slender

92.0

275

235

f

235 5.05.0

yw


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EXAMPLE 5

Double angle strut composed of two 100 x 75 x 10 S 355 angles

connected to gusset plates by the long legs back to back and

subject to axial compression

10

0mm

b

75 mm

Connected leg

Outstand leg

d

t , thickness

See figure 5.2 sheet 3 of the codeDimensions and Properties of the section are availableB=75 mm; d = 100 mm; t=10 mmb/t=75/10=7.5; d/t=100/10=10; (b+d)/10=17.5


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Table 9: Since t=10 mm (< 40 mm) therefore py=355 N/mm2

Table 5.2 sheet 3of3): For double angles with components separated underaxial compression :Class 1 and 2 are not applicable; For class 3 threecriteria must be satisfied to comply with a semi-compact classificationnamely d/t


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Outstand b/t=7.5 Limit values15 =15x0.81=12.15 satisfied

Connected leg d/t=10 Limit values

15 =15x0.81=12.15

satisfied

Combined (b+d)/2t=8.75 Limit value

11.5=11.5x0.81=9.315 satisfied

Since all three criteria are satisfied; section is class 3


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EXAMPLE 6

Determine the classification for section 356 x 127 UB 33 Grade 275

subject bending

Wpl,yy = 539.8 cm3 ; Iyy= 8200 cm4; B = 125.4 mm ; D = 348.5 mm ;

t = 5.9 mm ; T = 8.5mm ; r = 10.2 mm (figure next slide)

Table 5.2 is to be used.

92.0275

235

f

235 5.05.0

y

CompressionFlange Actualb/T= 5.82 Limits : 9, 10 149x0.92=8.28Flangeis plastic

Web: subjectto bending d/t =52.7


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EXAMPLE 7

Determine the classification for the welded section of steelgrade 355 used as compression member, shown below

400

T=10mm

D=420

t=10

Flange classification:

81.0355

235

9.1810

62/102002/2/

T

stBw

Limits are 9, 10and 14for welded sections

(same as for rolled sections)

Since 14


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EXAMPLE 8

Classify a hot rolled circular section 273.0 x 6.3 CHS S275 subject to

compression due to bending.

CHS =circular hollow section

6.3 mm

273 mm

D/t = 273/6.3 = 43.33

Table 3.1: since t = 6.3 mm ; fy = 275 N/mm2

92.0

275

235

f

235 5.05.0

y

Therefore:


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EN 1993 1-1 Table 5.2: The limiting values of D/t

Limiting

value

Actual D/t

Class 1

Plastic

502 50x0.922= 42.32 43.33

Class 2

Compact

702 70x0.922= 59.25

Class 3

Semi

compact

902 140x0.922=118.496

Since 42.32< actual D/t < 59.25; the section is

classified as compact

EXAMPLE 9


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EXAMPLE 9

The figure below shows a hot formed rectangular hollow section.

500mm

300 mm

The properties of the section are:

t=10 mm,

A = 155 cm2,

d/t = 47.0,

b/t = 27.

Determine the following:

A - Classification for section under flexure

ANSWER: Assuming S275 steel

92.0

275

235

f

235 5.05.0

y


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FLANGE:

c/tf={300- 2x10}/10=28 Compression flange /internal element :

choose part subject to compression whose limit for plastic section is

33=33 x0.92=30.36.flange is plasticuse table 5.2

Also -d/t=80x 147 =33 ..since. b/T


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STEP 1

Assuming S275 steel

Thickness of flange = 10 mm < 40 mm.fyf= 275 N/mm2

Thickness of web = 10mm < 40mm.fyw=275 N/mm2

STEP 2

= (235/275)0.5= 0.92

STEP 3Flange aspect ratio , b/T = 27

Compression flange /internal element : choose part subject to

compression whose limit for plastic section is

33=33 x0.92=30.36.flange is plasticuse table 5.2

B- The axial compressive load below which the section is non-slender


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Web aspect ratio , d/t = 47

For web in compression, the limiting value

of d/t is 33, 38and 42

Actual d/t=47.0 Therefore the web is

Slender.

The section takes the lowest classification

for flange and web

So the section is slender.

Documents

Tutorial 1- Properties and Section Classification