SHEAR LAG AND DISTORTIONAL BEHAVIOUR OF LAMINATED COMPOSITE BOX BEAMS

Abstract

Box girders, often used as basic components in modem bridge structures made of steel or Prestressed concrete or of Composites, have gained wide acceptance in freeway and bridge systems due to their structural efficiency, better stability, serviceability, economy of construction and pleasing aesthetics. More over it has got some other features such as high torsional rigidity, high bending stiffness, high transverse strength & economy due to hollow section. Composite materials are ideal for structural applications where high strength to weight ratio and stiffness to weight ratios are required as compared to conventional structural materials like steel, aluminium and other types of metals. In recent years, fast growing interest in composite materials for infrastructure rehabilitation and new construction provides opportunity for the development of FRP bridge decks. But high degree of orthotropy and anisotropy in the beam panels causes unexpected enhancement in non classical effects like shear lag, distorsion etc. So the design is complex with Composites as compared to traditional engineering materials, which are isotropic in nature. Hence understanding these non classical effects such as shear lag and distorsion are very much needed in this case. Various studies are reported in the shear lag and distorsional behaviour in isotropic steel sections, where as more studies are required for these phenomenon in the case of laminated composites. In the present work shear lag and distorsional behaviour of laminated composite box beams are studied in detail. FEM modelling of laminated composite box made using ANSYS 11.0 package. The various factors that affect the shear lag such as the effect of various kinds of loadings, the effect of variation of cross sectional parameters, the effect of various support conditions, the effect of fibre orientations and the effect of different cell types on shear lag of laminated composites are studied using effective width concept. The results obtained can predict the phenomenon in the case of laminated composites of various types. For distorsional behaviour in laminated composites certain key parameters are identified and defined. Graphs showing the variation of distorsional and warping parameters are developed for FRP box beam. Variation of these distorsional and warping parameters are studied for various fibre orientations. Various methods to reduce the distorsion are also studied in this which includes the effect of different cell types and the effect of intermediate diaphragms.