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D5.C.5.3 Members Subject to Shear

The cross section capacity of a member subject to shear is checked as per Cl. 6.2.6 of the code. The condition to be satisfied is:

V E d V c , R d 1.0
the is the shear design resistance given by:
V c , R d = V p l , R d = A v ( f y / 3 ) γ M 0
the shear area and is worked out for the various section types as given in Cl. 6.2.6(3) of the code

Shear Buckling

For sections that are susceptible to shear buckling, the program will perform the shear buckling checks as given in Section 5 of EN 1993-1-5. The shear buckling checks will be done only for I –Sections and Channel sections. Shear stresses induced from torsional loads are taken into account while performing torsion checks.

Note: Web shear buckling is checked in STAAD.Pro V8i (SELECTseries 3) (release 20.07.08) and later.

The susceptibility of a section to shear buckling will be based on the criteria given in Cl 5.1(2) of EN 1993-1-5 as is as given as follows:

  1. For unstiffened webs, if h w / t > 72 × ε / η , the section must be checked for shear buckling.

    The design resistance is calculated as:

    V b , R d = V b w , R d η f y w h w t 3 γ M 1
    V b w , R d = χ w f y w h w t 3 γ M 1
    distance between flanges of an I Section (i.e., depth - 2x flange thickness)
    thickness of the web
    √(235/fy), where fy is the yield stress
    1.2 for steel grades up to and including S 460 and

    = 1.0 for other steel grades

    as defined in sections below
    the web contribution factor obtained from Table 5.1 of the EC3 code and is evaluated per the following table:
    Table 1. Evaluate of χw
    Slenderness Parameter Rigid End Post Non-rigid End Post
    λ ¯ w < 0.83 / η η η
    0.83 / η λ ¯ w < 1.08 0.83 / λ ¯ w 0.83 / λ ¯ w
    λ ¯ w 1.08 1.37 0.7 + λ ¯ w 0.83 / λ ¯ w
    λ ¯ w
    h w 86.4 × t × ε
  2. For stiffened webs, if h w / t > 31 × E k τ / η , the section must be checked for shear buckling.

    The design resistances considers tension field action of the web and flanges acting as struts in a truss model. This is calculated as:

    V b , R d = V b w , R d + V b f , R d η f y w h w t 3 γ M 1


    the flange resistance per Cl.5.4 for a flange not completely utilized by bending moment
    h f t f 2 f y f c γ M 1 [ 1 ( M E d M f , R d ) 2 ]
    the width of the flange which provides the least axial resistance, not to be taken greater than 15εtf on each side of the web
    the thickness of the flange which provides the least axial resistance
    Mf,kM0 , the moment of resistance of the cross section consisting of the effective area of the flanges only. For a typical I Section or PFD, this is evaluated as b·tf·hw . When an axial load, NEd, is present, the value of Mf,Rd is reduced by multiplying by the following factor:
    1 N E d [ ( A f 1 + A f 2 ) f y f γ M 0 ]
    Af1 ,Af2
    the areas of the top and bottom flanges, respectively
    a ( 0.25 + 1.6 b f t f 2 f y f t h w 2 f y w )
    transverse stiffener spacing. The equation of c is likewise used to solve for a sufficient stiffener spacing in the case of demand from loads exceeding the calculated capacity for a specified stiffener spacing

The following equation must be satisfied for the web shear buckling check to pass:

η 3 = V E d V b , R d 1.0
the design shear force
Note: The shear forces due to any applied torsion will not be accounted for if the TOR parameter has been specifically set to a value of 0 (i.e., ignore torsion option).

If the stiffener spacing has not been provided (using the STIFF parameter), then the program assumes that the member end forms a non-rigid post (case c) and proceeds to evaluate the minimum stiffener spacing required.