Shear capacity (Beams: EC3 Eurocode)

Major and minor axis shear

Checks are performed according to clause 6.2.6 (1) for the absolute value of shear force normal to each axis at the point under consideration.The following points should be noted:

No account is taken of fastener holes in the flange or web - see 6.2.6 (7)
Shear is not combined with torsion and thus the resistance is not reduced as per 6.2.6 (8)

Web Shear buckling

Shear web buckling design applies to rolled and plated I/H sections only.

National Annex dependency

Plates with unstiffened webs are checked for shear web buckling where:

h_w / t_w > 72 ε / η

where

ε = √ (235 / f_w

η is NA dependant and is defined in the table below:


National Annex	η	Applicable to
Eurocode value	1.20	Up to and including S460, else use η = 1.00
UK	1.00	All steel grades
Irish	1.00	All steel grades
Malaysia	1.00	All steel grades
Singapore	1.00	All steel grades

Contribution from flanges

When the flange resistance is not fully utilized in resisting the bending moment (M_Ed <M_f,Rd), the contribution from the flanges is taken as:

V_bf,Rd = (b_f t²_f f_yf) / (c γ_M1) * (1 - (M_Ed/M_f,Rd)²)

where

b_f and t_f are taken for the flange which provides the least axial resistance
b_f is not taken as larger than 15εt_f on each side of the web
M_f,Rd is the moment of resistance of the cross section consisting of the effective area of the flanges only
c = a (0.25 + 1.6b_f t_f² f_yf / t h_w² f_yf_w)
a is the distance between stiffeners

As we are only designing for the case where no stiffeners are being used, a → ∞ therefore c → ∞ so V_bf,Rd→ 0.

Contribution from the web

The contribution from the web is taken as:

V_bw,Rd = (x_w f_yw h_w t) / (√3γ_M1)

x_w ≤ η

Design resistance

The design resistance for shear is taken as:

V_b,Rd = V_bw,Rd + V_bf,Rd ≤ η (f_yw h_w t) / (√3γ_M1)

Influence of shear

According to 7.1 of EN 1993-1-5 provided V_Ed ≤ 0.5 V_bw,Rd the design resistance to bending moment and axial force does not need to be reduced to allow for shear force.

In Tekla Structural Designer V_Ed is restricted to 0.5 V_bw,Rd, values above this are deemed beyond scope.

This restriction is only applicable if h_w / t_w > 72 ε / η

Assumptions

The following points should be noted:

Non-rigid end post is a more conservative approach than a rigid end post.
Physical support conditions can be taken as equivalent to "transverse stiffeners at supports only".
It is assumed there is negligible contribution to the design shear force VEd from shear from torque
All hole cut outs are small in accordance to section EN 1993-1-5:2006 2.3
As the case being designed for is where no stiffeners are being used, a → ∞ therefore c → ∞ so V_bf,Rd→ 0.
If a grade of steel is used other than S335, S355 and S460, η will be taken as 1.00 regardless of National Annex.