Tension members - The Behaviour and Design of Steel Structures to EC3 - page 45

minor ( z ) axis, EC3 allows

2

N t , Ed / N pl , Rd − a
1 − a

M z , Ed ≤ M N , z , Rd = M pl , z , Rd 1 − ≤ M pl , z , Rd , (2.24)

where M N , z , Rd isthereducedplasticdesignmomentresistanceabouttheminor( z )
axis.
EC3 also provides an alternative to equation 2.21 for the section resistance to
axial tension and bending about both principal axes of Class 1 or Class 2 cross-
sections.This is the more accurate interaction equation (see Section 7.4.2)
M y , Ed
M N , y , Rd

α β

M z , Ed
M N , z , Rd

+ ≤ 1,

(2.25)

where the values of α and β depend on the cross-section type (e.g. α = 2.0 and
β = 5 N t , Ed / N pl , Rd for I-sections and α = β = 2 for circular hollow sections).
A worked example of a tension member with bending actions is given in
Section 2.7.5.

2.6.4.2 Member resistance

EC3 does not provide any specific rules for determining the influence of lateral
buckling on the member resistance of tension members with bending. This may
be accounted for conservatively by using

M y , Ed ≤ M b , Rd (2.26)

in equation 2.21, in which M b , Rd is the design buckling moment resistance of the
member (see Section 6.5). This equation conservatively omits the strengthening
effect of tension on lateral buckling. A less conservative method is provided by
equations 2.14-2.17.

2.7 Worked examples

2.7.1 Example 1 - net area of a bolted universal column
section member

Problem. Both flanges of a universal column section member have 22 mm diam-
eter holes arranged as shown in Figure 2.11a. If the gross area of the section is
201 × 10 2 mm 2 and the flange thickness is 25mm, determine the net area A net of
the member which is effective in tension.

Solution. Using equation 2.6, the minimum stagger is s m = √ ( 4 × 60 × 22 ) =
72.7mm > 30mm = s . The failure path through each flange is therefore stag-
gered,andbyinspection,itincludesfourholesandtwostaggers.Thenetareacan