INFLUENCE OF FLANGE STIFFNESS ON DUCTILITY BEHAVIOUR OF PLATE GIRDER: INTRODUCTION(2)

Influence Of Flange Stiffness_decrypted
This expression has been shown as more effective and further reduced to extreme cases such as girders with weak flanges, strong flanges and thick web. In the case of weak flanges, the value of flange strength becomes very small and it is neglected from the equation. When the flanges are very strong, it was assumed that the distance of the plastic hinge, c, away from the end of the panel increases and becomes equal to the panel width, b, the hinges formed at four corners of the panel to form a ‘picture frame’ mechanism. The tension field was assumed to act at an angle of 45o and the value of ‘ c’ was considered as equal to ‘b’ to obtain the limiting value of shear capacity. In the case of a girder with thick web, they assumed that the web may yield before it buckles so that no tension field action would develop. The theory proposed by Porter et al has been validated by checking with experimental results reported by a number of researchers.

The development of tension field and collapse mechanism of shear panels isolated from plate girders were studied using the finite element method by Kuranishi et al (1988). Special attention was paid to the influence of the rigidity of flanges and the boundary conditions of web panel. It was found that no plastic hinge appeared in flanges ever in the ultimate state, and that a collapse mechanism was formed when the yielded zones propagate completely in the diagonal direction of the panel. Kuranishi et al (1988) considered four different panel aspect ratios viz. 0.5, 0.75, 1.0 and 1.5 and three different web slenderness ratios such as 152, 180 and 250 in their numerical study. Shanmugam and Baskar (2003), vice-verse, have carried out experimental and numerical investigation on steel-concrete composite plate girders. Two bare steel plate girders and ten steel-concrete composite plate girders with two different d/t ratios of web plate and varying Mp/M ratio of flanges were considered in the investigation. It was noticed from these experimental and numerical studies that the stiffness of the flanges greatly influences the post yield behaviour of the plate girders. Further numerical investigation is made in this present study using four different bare steel plate girders with d/t ratios of 250, 150, 125 and 94 which are named as SPG1, SPG2, SPG3 and SPG4, respectively. A constant panel aspect ratio 1.5 is considered for all the girders.

The previously tested girders (Baskar & Shanmugam, 2003), SPG1 and SPG2 are considered as reference girders and the numerical investigation is made by varying the flange stiffness over the girders. SPG3 and SPG4 are subjected to only numerical study and the results obtained from the studies are presented herein.

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