Explain web bucking and web crippling in a beam
1 Answer

Web Buckling and Web Crippling

  • A heavy concentrated load or end reaction produces a region of high compressive stresses in the web either at support or under the load.

  • This causes the web either to buckle or to cripple (or local bending).


(a) Web Buckling


(b) Web Crippling


  • Web buckling occurs when intensity of compressive stress near the center of the section exceeds the critical buckling stress of web acting as a strut.

  • At supports and under a concentrated load, certain portion of the beam acts as a column to transfer the load.

  • Under this compressive force the web of the beam section may buckle.

  • The load dispersion angle may be taken as 45 degrees.

  • Hence the section should be checked for web buckling.

  • The rolled sections are provided with suitable thickness for web so that web buckling is avoided.

  • The probability of web buckling is more in the case of built- up sections having greater ratio of depth to thickness of the web.

  • At the point of concentrated load web may be considered as a strut between the beam flanges.

  • The load is assumed to disperse over the length of (b,+n,)., where (b,) is the stiff bearing length and (n,) is the dispersion of the load through the web at 45 degrees, to the level of half the depth of cross-section

  • In case of built-up sections, it is necessary to check for buckling of web and provide web stiffeners.

  • Effective web buckling strength is to be found based on the cross-section of web [(b,+n,)tw].

  • Fcdw = [(b,+n,)t,]f.

  • Fcdw = Web buckling strength

  • f. = allowable compressive strength corresponding to the assumed web column corresponding to its slenderness ratio and effective length

  • Effective length= 0.7d

  • d= depth of the strut between the flanges= =[Total depth- 2*(tr + R1)]

  • radius of gyration = r, = S(l,/A) = t/(2/3)

  • slenderness ratio = 0.7d/r, = 2.42d/tw


  • Concentrated loads and reactions are resisted by compressive stresses in the web of steel beams.
  • Therefore web is acted upon by large amount of stresses at these locations.

  • Stress concentration occurs at the junction of the web and the flange, as a result large bearing stresses are developed. At these locations, web tends to fold over the flange.

  • This type of local buckling is called as web crippling.

  • Web crippling is the buckling of the web due to the compressive force delivered through the flange.

  • So, the concentrated load should be transferred from flanges to the web on sufficiently large bearing areas.

  • The root of the fillet is the most critical location for failure.

  • In the case of web crippling at a support, the crippling strength of the web is given by: Fw = (b1+n2)twfyw/Tm0

  • Where b1= stiff bearing length; fyw = yield strength of web

  • n2 = dispersion length through the flange to the web junction at a slope of 1:2.5 to the plane of flange.

  • At the point of application of a concentrated load,

    Fw = (b1+2n:)twfyw/Tmo

  • Since the dispersion of the load takes place on either side.

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