Contribution of longitudinal stiffener rigidity and position to bridge girder integrity

To increase the elastic critical load of a plate, such as I-shaped cross-welded section of bridge girders and upgrade bending and torsional stiffnesses, slenderness is usually reduced by dividing the web into subpanels, by means of transversal stiffeners and a longitudinal stiffener. The optimal solution is defined when the stiffener maximizes the buckling coefficient, with a minimal cross-section area. For this purpose, seven shapes of open and closed sections of longitudinal stiffeners, with different second moment of area, are examined in terms of buckling coefficients by theoretical solution and numerical computation, to compare their contribution in terms of weight per linear meter of beam. The optimum value of flexural stiffness is defined and a useful practical law is given to correlate the best position of a conventional flat stiffener with respect to variations of the stress gradient, from pure bending to pure compression, to maximize the benefits of its action and increase the stability of bridge girders.