INFLUENCE OF FLANGE STIFFNESS ON DUCTILITY BEHAVIOUR OF PLATE GIRDER: INTRODUCTION(1)

INTRODUCTION(1)

Rockey and Skaloud (1968, 1972) showed that for plate girders having proportions similar to those employed in civil engineering, the ultimate load capacity is greatly influenced by the flexural rigidity of the flanges. They showed that the collapse mode of the plate girders involve development of plastic hinges in tension and compression flanges. Rockey and Skaloud conducted ultimate load tests on three series of plate girders in each of which only the size of the flanges, and therefore their flexural rigidity, was varied. The position of the internal hinges was found to vary with flange stiffness, the value ā€˜cā€™, which defines the position of plastic hinge, increasing from near zero in the case of flexible flanges to approximately 0.5b when the flanges are strong. It is also proved experimentally that it is possible to increase the ultimate shear strength of the web to the extent of 60% by simply increasing the flexural rigidity of the flange.

Porter et al (1975) presented an equilibrium solution to calculate the ultimate strength of plate girders. It is assumed that the web panels are simply supported along its boundaries; this assumption obviously leads to lower limit. Fujii (1968), Chern and Ostapenko (1969) and Komatsu (1971), on the other hand assumed that the flanges provide a fully clamped condition and the vertical stiffeners providing a simple edge support. The correct buckling solution lies somewhere between these two extreme solutions. Porter et al, also assumed that the effect of bending stresses on the shear buckling stress of the web and the variation of over the web panel could be ignored.

Based on their experimental observation and equilibrium approach, Porter et al (Ref) proposed the expression shown in Eqn. 1 to calculate the ultimate shear carrying capacity of steel plate girders.

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