AISC LRFD 1.pdf

72 FLANGES AND WEBS WITH CONCENTRATED FORCES [Sect. K1.When the concentrated force to be resisted is applied at a distance from the memberend that is less than 10t f , R n shall be reduced by 50 percent.When transverse stiffeners are required, they shall be welded to the loaded flange todevelop the welded portion of the stiffener. The weld connecting transverse stiffenersto the web shall be sized to transmit the unbalanced force in the stiffener to theweb. Also, see Section K1.9.3. Web Local YieldingThis Section applies to single-concentrated forces and both components ofdouble-concentrated forces.Either a pair of transverse stiffeners or a doubler plate, extending at least one-halfthe depth of the web, shall be provided adjacent to a concentrated tensile or compressiveforce when the required strength of the web at the toe of the fillet exceedsR n ,where = 1.0and R n is determined as follows:(a) When the concentrated force to be resisted is applied at a distance from themember end that is greater than the depth of the member d,R n = (5k + N)F yw t w(K1-2)(b) When the concentrated force to be resisted is applied at a distance from themember end that is less than or equal to the depth of the member d,R n = (2.5k + N)F yw t w(K1-3)In Equations K1-2 and K1-3, the following definitions apply:F yw = specified minimum yield stress of the web, ksi (MPa)N = length of bearing (not less than k for end beam reactions), in. (mm)k = distance from outer face of the flange to the web toe of the fillet, in. (mm)t w = web thickness, in. (mm)When required, for a tensile force normal to the flange, transverse stiffeners shall bewelded to the loaded flange to develop the connected portion of the stiffener. Whenrequired for a compressive force normal to the flange, transverse stiffeners shalleither bear on or be welded to the loaded flange to develop the force transmitted tothe stiffener. The weld connecting transverse stiffeners to the web shall be sized totransmit the unbalanced force in the stiffener to the web. Also, see Section K1.9.Alternatively, when doubler plates are required, see Section K1.10.4. Web CripplingThis Section applies to both compressive single-concentrated forces and the compressivecomponent of double-concentrated forces.Either a transverse stiffener, a pair of transverse stiffeners, or a doubler plate,extending at least one-half the depth of the web, shall be provided adjacent to a concentratedcompressive force when the required strength of the web exceeds R n ,LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION