Distortional response of doubly symmetric laminated composite box girder

Abstract

Analysis for longitudinal bending and pure torsion of box girder can be made by means of elementary theories while distortional effects in the box girder cannot be predicted by these theories. Due to thinness of the laminated composite box walls, generalized loads applied to this structure give rise to warping and distortion of the cross-section. The phenomenon distortion is undesirable as it alters the geometry of the box cross-section and generates some additional stresses thereby reducing the bearing capability of the box girder. The objective of this paper is to understand distortional response of doubly symmetric i.e. rectangular laminated composite box girder for various geometrical parameters. In this study, distortional performance of a single span single cell simply supported laminated composite FRP rectangular straight box girder section is studied for 0°, ±45°, 90° fiber orientations using BEF analogy method for different geometrical parameters. A procedure is derived for warping and distortion of FRP box-girder using BEF analogy method considering a 4th order differential equation. The orthotropic nature of FRP has to be taken into consideration in this analysis. It is observed that from distortional considerations, the box girder section should be proportioned to have large span to depth ratio and increase in the web thickness, the distortion stresses will decreases. There is not significant increase in the distortional stresses and warping stresses with increment of length of side cantilever for lower span to depth ratios. It is also be observed that the distortion stress increases and warping stresses decreases with span for same span to depth ratio.