(h/tw ) 2 Fyw Flexure-Shear Interaction

Plate girders designed for tension field action must satisfy the flexure-shear interaction criterion in regions where 0.60f Vn < Vu < fVn and 0.75f Mn < Mu < f Mn Bearing Stiffeners

Bearing stiffeners must be provided for a plate girder at unframed girder ends and at points of concentrated loads where the web yielding or the web crippling criterion is violated (see Section Bearing stiffeners shall be provided in pairs and extend from the upper flange to the lower flange of the girder. Denoting bst as the width of one stiffener and tst as its thickness, bearing stiffeners shall be portioned to satisfy the following limit states:

For the limit state of local buckling:

For the limit state of compression: The design compressive strength, f cPn, must exceed the required compressive force acting on the stiffeners. f cPn is to be determined based on an effective length factor K of 0.75 and an effective area, Aeff, equal to the area of the bearing stiffeners plus portion of the web. For end bearing, this effective area is equal to 2(bsttst) + 12^; and for interior bearing, this effective area is equal to 2(bsttst) + 25^, where tw is the web thickness. The slenderness parameter, 1c, is to be calculated using a radius of gyration, r = ^J(I^/Af), where 1st = tst(2bst + tw )3/12.

For the limit state of bearing: The bearing strength, f Rn, must exceed the required compression force acting on the stiffeners. f Rn is given by fRn > 0.75[1.8FyApb] (4.98)

where Fy is the yield stress and Apb is the bearing area. Intermediate Stiffeners

Intermediate stiffeners shall be provided if

• The shear strength capacity is calculated based on tension field action.

• The shear criterion is violated (i.e., when the Vu exceeds fvVn).

Intermediate stiffeners can be provided in pairs or on one side of the web only in the form of plates or angles. They should be welded to the compression flange and the web but they may be stopped short of the tension flange. The following requirements apply to the design of intermediate stiffeners:

Local buckling: The width-thickness ratio of the stiffener must be proportioned so that Equation 4.97 is satisfied to prevent failure by local buckling. Stiffener area: The cross-section area of the stiffener must satisfy the following criterion:

where Fy is the yield stress of stiffeners, D = 1.0 for stiffeners in pairs, D = 1.8 for single angle stiffeners, and D = 2.4 for single plate stiffeners.

The other terms in Equation 4.99 are defined as before in Equations 4.94 and 4.95.

Stiffener moment of inertia: The moment of inertia for stiffener pairs taken about an axis in the web center or for single stiffeners taken about the face of contact with the web plate must satisfy the following criterion:

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