1

CSE 362 Design of Steel Structures Web crushing and web buckling

Professor K.F. ChungProfessor K.F. Chung

Department of Civil and Structural EngineeringThe Hong Kong Polytechnic UniversityHong Kong SAR, China

2

Web crushing and web bucklingBS5950: Part 1 (1990)

Both failure modes are critical in the section webs under concentrated loads.

Vertical stiffeners shall be provided whenever necessary.

b1

b1

3

Web crushing in a very short beam

Yielding in compression

Pwc = py x Awc

where Awc = b1 x t

Tr

b1

4

0.5n2 = 2.5(T + r)

Pwc = py x [b1 + 5(T + r)] t for internal condition

0.5n2

Conc. Load

0.5n2 b1

Fla

nge

thic

knes

s T

Roo

f ra

dius

r

1 : 2.5

Web crushing in normal situation

5

Pwb = pc x Awb

where pc is determined with λ (= 2.5 d / t), and use the column buckling curve ‘c’.

Awb = b1 x t

d

b1

Web buckling in a very short beam

6

45° 45°

0.5n1

Conc. Load

0.5n1 b1

D

0.5 n1 = 0.5D

Pwb = pc x Awb

where pc is determined with λ (= 2.5 d / t), and use the column buckling curve ‘c’.

Awb = (b1 + D) x t

Web buckling in normal situation

7

Web bearing and web bucklingBS5950: Part 1 (2000) and HKSC (2005)

Both failure modes are critical in the section webs under concentrated loads.

Web bearing (crushing) resistance, Pbw

Pbw = (b1 + n k) t pyw

where b1 is the stiff bearing lengthn = 5 in general except at the end of a member

= 2 + 0.6be/k at the end of member k = T + r for a rolled I- or H-section

= T for a welded I- or H-sectionbe is the distance to the nearer end of the member from the end

of the stiff bearing

8

Web buckling resistance, Px

bw1

ex P

d k)n (b

tε 25

d4.1

0.7d aP

+

+=

i) Near beam end where ae < 0.7 d

bw1

x Pd k)n (b

tε 25P

+=

ii) Away from beam end where ae ≥ 0.7 d

ae is the distance from the load or reaction to the nearer end of the member.

Web bearing and web bucklingBS5950: Part 1 (2000) and HKSC (2005)

Both failure modes are critical in the section webs under concentrated loads.