Optimised fibre reinforced polymer bridge design using variable angle tow composites

Fibre-reinforced polymers (FRP) are increasingly adopted in bridge structures to reduce their environmental impact, extend service life and save costs. These results are achieved thanks to the high stiffness and strength-to-weight ratios, the faster installation time and the superior resistance to environmental degradation of FRP composites compared to traditional building materials. In this work, we propose the use of composite laminates called Variable Angle Tow (VAT) in bridge structures. Unlike traditional laminates characterised by straight fibres, VAT laminates have fibre orientations that change pointwise across the structure, following curvilinear paths. This feature enhances the stiffness tailoring capabilities and allows for more optimised designs. In aerospace engineering, VAT composites have successfully tailored structural stiffness to improve linear elastic response, reduce buckling phenomena, and optimise postbuckling behaviour. However, VAT laminates have not yet been applied in civil structures. This work shows that using VAT composite laminates in a bridge girder improves buckling and postbuckling behaviours and increases overall stiffness. The benefits provided by VAT composite laminates to the structural performance of bridge girders are demonstrated through a parametric numerical study and a multi-objective optimisation. For different spans, results show that VAT laminates exhibit a buckling load up to 80% over traditional straight fibre laminates, with equal or lower deflections and without adding extra material, opening new design scenarios for bridge structures.