Improving strength and ductility of continuous composite plate girder bridges

The ultimate load carrying capacity of continuous composite plate girder bridges is usually limited by the local buckling failure of steel girders at interior supports. This paper presents a simple reinforcement method which changes the failure mechanism of the continuous girder from local buckling to formation of plastic hinges at the interior supports and mid-span. Such a change in failure mechanism greatly improves the strength and ductility of the superstructure. In this method the compressive portion of the web near the interior support is braced against local buckling by bolting pairs of stiff bracing elements on opposite sides of the web. The bracing elements prevent local buckling failure of the support section and create a section which can rotate inelastically at plastic moment allowing the second hinge to form at mid-span. The bracing elements may be plates or longitudinal stiffeners which should be designed to remain elastic while the section undergoes plastic deformation. The behavior of plate girders which are reinforced by such bracing elements is studied using nonlinear finite element analyses.