5003 Lectures - Faculty of Engineering and Applied Science

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E5003 - Ship Structures I 212 © C.G. Daley are implicitly assuming that the flange is uniformly compressed (or stretched), and that the compressive or tensile stresses are uniform in the flanges. Recall that ‘standard’ formula;
E5003 - Ship Structures I 213 © C.G. Daley When we a lateral load (a bending load) to a beam or ship frame, the web carries the load and tends to bend. The flange is attached at the edges of the web and as the web bends, its edge shortens (or lengthens) and tends to pull the flange with it. To pull on the flange, a shear stress of applied to the edge of the flange. As shown in the sketch, the flange is acted upon along its edge. Its as if the flange is pinched along its edge, causing the flange to compress more near the web and less away from the web. Unfortunately there are no general analytical solutions for shear lag and effective width. Certain approximate solutions have been postulated (see PNA, VI, pp 247-250) Shear lag and diminished effective width are most important in cases of ; • wide flanges (large b) • short frames (small L/b) • proximity to free ends • proximity to concentrated loads Finite element programs, when shell or brick elements are used to model the frames, will naturally show the shear lag effects. There have been experiments on hull girder models that have shown not only a variation in deck stresses, but actual stress reversals. This means that even when the average deck stress is compressive, there may be a part of the deck (at center) where the stresses are tensile, with the
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5003 Lectures - Faculty of Engineering and Applied Science

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