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Short Paper Proc. of Int. Conf. on Structural and Civil Engineering 2011

Shear Behaviour of Stiffened Plate Girders Ajeesh S S1 and Sreekumar S2 1

College of Engineering, Trivandrum Email: ss_ajeesh@yahoo.co.in 2 College of Engineering, Trivandrum Email: sks101y@yahoo.com usually slender in cross section and are susceptible to buckling phenomenon. The elastic buckling stress (ôcr) of a rectangular web plate (width c, depth d and thickness tw) was given [5] as

Abstract—This paper deals with the shear behaviour of steel plate girders under varying parameters such as aspect ratio, web slenderness ratio, ratio of flange to web thickness and the position of longitudinal stiffener. The effect of these parameters on critical shear strength was compared analytically using finite element analysis. It was numerically demonstrated that the shear resistance of plate girder decreases with increase in aspect ratio and web slenderness ratio. The presence of thick flange improves the shear buckling strength of plate girder. The effective position of longitudinal stiffener is at mid height of the web panel so that maximum shear resistance can be achieved.

Where E=Young’s modulus of elasticity, µ=Poisson’s ratio and k=web shear buckling coefficient. The web shear buckling coefficient ‘k’ is a key factor influencing the shear strength of plate girder. The boundary of web panel was assumed to be simply supported in order to find the value of shear buckling coefficient in theoretical formulations. The shear buckling coefficient for simply supported edge condition is given by

Index Terms—Girder; Shear resistance; Steel

I. INTRODUCTION Plate girder is a deep flexural member fabricated using steel plates by riveting, bolting or welding. The primary functions of the web plate in a plate girder are to maintain the relative distance between the top and bottom flanges and to resist the introduced shear forces. In most practical ranges of span lengths for which a plate girder is designed, the induced shear force is relatively low as compared with the axial forces in the flanges resulting from flexure. As a result, the thickness of the web plate is much smaller than that of the flanges. Consequently, the web panel buckles at a relatively low value of the applied shear loading. The web of plate girder is often reinforced with transverse and longitudinal stiffeners to increase their buckling strength, and the web design involves finding a combination of optimum plate thickness and stiffener spacing that renders economy in terms of material and fabrication cost. Finite element analysis of longitudinally stiffened plates subjected to shear loading was discussed in the literature [1 and 4]. Experimental and numerical investigation was conducted to study the shear response of stainless steel plate girders [2]. Nonlinear finite element analysis on three dimensional models of transversely stiffened plate girder models subjected to pure shear was reported [3]. The present analytical study is mainly concentrated on the shear resisting parameters of the plate girder namely aspect ratio of the web panel, web slenderness ratio, ratio of flange to web thickness and the position of longitudinal stiffener.

The shear stress (τ) acting on the web panel of plate girder is resisted by the principal compressive stress and tensile stress (σ) in the elastic range. This mechanism continues till shear buckling stress (τcr) of material is reached. Once buckling occurs, the web panel has no more compression capacity and it remains equal to critical shear stress. Therefore further increase in load is resisted by an increase in the principal tensile stress and the web panel behaviour is governed by a tension field due to the formation of plastic hinges (Fig. 1). The nonlinear shear stress and normal stress interaction that takes place from the onset of elastic shear buckling to the ultimate strength state (Vu) is known as postbuckling shear strength. The ultimate failure of the girder is due to yielding of the web panel and it is governed by von Mises yield criterion. The von Mises yield stress (fvn) for pure shear condition depends on the yield stress of web panel (fyw) and it is given by

II. SHEAR RESISTANCE OF PLATE GIRDER The shear design methods of plate girder web panel was divided into two categories: (1) allowable stress design based on elastic buckling as a limiting criterion; and (2) strength design based on ultimate strength, including postbuckling shear strength as a limit state. The web panel of plate girder is © 2011 ACEE DOI: 02.SCE.2011.01. 3

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