Compression members - The Behaviour and Design of Steel Structures to EC3 - page 92

Bucklingwilloccuraboutthemajor( y )axis.ForarolledUCsection(with h / b ≤
1.2 and t f ≤ 100 mm), buckling about the y -axis, use buckling curve (b) with
α = 0.34 T6.2,T6.1

Φ y = 0.5 [ 1 + 0.34 ( 2.322 − 0.2 ) + 2.322 2 ]= 3.558

6.3.1.2(1)

1

χ y = √

3.558 2 − 2.322 2 = 0.160

6.3.1.2(1)

3.558 +

which is much less than the guessed value of 0.5.
Second section choice .

Guess χ = ( 0.5 + 0.160 )/ 2 = 0.33
A ≥ 561 × 10 3 /( 0.33 × 355 ) = 4789 mm 2

Try a 203 × 203 UC 52, with A = 66.3 cm 2 , i y = 8.91 cm, t f = 12.5 mm.
For S355 steel with t f = 12.5 mm, f y = 355 N/mm 2

EN 10025-2

ε = ( 235 / 355 ) 0.5 = 0.814 T5.2
c f /( t f ε) =[ ( 204.3 − 7.9 − 2 × 10.2 )/ 2 ] ( 12.5 × 0.814 ) = 8.65 < 14 T5.2
c w /( t w ε) = ( 206.2 − 2 × 12.5 − 2 × 10.2 )/( 7.9 × 0.814 ) = 25.0 < 42

T5.2

and so the cross-section is fully effective.

N cr , y = L cr , y

Af y 1

λ 1 =

12000
( 8.91 × 10 )

1
93.9 × 0.814 = 1.763 6.3.1.3(1)

λ y =

i y

For a rolled UC section (with h / b ≤ 1.2 and t f ≤ 100 mm), buckling about the
y -axis, use buckling curve (b) with α = 0.34 T6.2,T6.1

Φ y = 0.5 [ 1 + 0.34 ( 1.763 − 0.2 ) + 1.763 2 ]= 2.320 6.3.1.2(1)

1

χ y = √

2.320 2 − 1.763 2 = 0.261

6.3.1.2(1)

2.320 +

γ M 1 = 0.261 × 66.3 × 10 2 × 355

N b , y , Rd = χ Af y = 615 kN > 561 kN = N Ed

6.3.1.1(3)

1.0

and so the 203 × 203 UC 52 is satisfactory.

3.12.3 Example 3 - designing an RHS compression member

Problem. Designasuitablehot-finishedRHSofS355steeltoresisttheloadingof
example 1 in Section 3.12.1.