DISTORTIONAL ANALYSIS OF LAMINATED COMPOSITE BOX GIRDERS

Abstract

The box girder is suitable for highway bridges because its high torsional stiffness can lead to a transversely uniform distribution of flange stresses for transversely non-uniform loading. Analysis for longitudinal bending and pure torsion can be made by means of elementary theories while distortional effects in the box girders cannot be predicted by these theories. The distortional action of the box girder consists of (a) transverse deformation and (b) longitudinal deformation (warping). Laminated composites, which are of orthotropic nature and earlier limited to aerospace applications, are gradually being applied in structural applications. Because of its orthotropic nature, study of distortional effect in laminated composite box beams assumes foremost importance. In the present work the effect of orthotropy due to fiber orientations is studied by changing the orthotropy ratio of different elements of the FRP single- cell box beam subjected to the distortional loading. Similarly, the effect of cross-sectional parameters on the distortional stresses is also studied. All these analyses are carried out by using the FEM package ANSYS 7.1. Then BEF charts are developed for 0, ± 45, 90 fiber orientations of the box beam and these charts are validated for different cross-sections as well as different geometrical properties. Numerical studies shows that top flange and web orthotropy have '.3ignificant influence on distortional stresses while bottom flange orthotropy has less impact. It is also observed that the distortional stresses are decreased for large span to depth ratio and for greater web thickness. The developed BEF charts are general in nature and provided upper and lower limits on 'w' and 'm' parameters and will be useful in the design of FRP box beam from distortional behaviour point of view.