The hybrid FRP and glass bridge

Abstract

This thesis focuses on the collaboration of two innovative materials - Fibre Reinforced Polymers (FRP) and structural glass – in the design of a (hybrid) footbridge with a 30 meter span. The choice of subject is led by a rising popularity of these materials in bridge design and strengthened by positive recent developments in conceptual small-scale FRP & glass hybrid structures. This research will try to take previous research one step further and will combine the advantages of both materials to reach a structurally efficient bridge design. The research question is as follows: “Can a hybrid pedestrian bridge with a loadbearing structure of FRP and structural glass be designed while making optimal use of the material properties of both materials?”.
The design by research process is divided in multiple steps. First of all a theoretical framework is created, with state-of-the-art information about the material properties of glass and FRP. This theoretical framework resulted - via design rules - in several preliminary design variants of which the structurally most efficient, most transparent and safest variant is chosen and subsequently elaborated on. The chosen variant is optimized by using a form-finding and geometric optimization process powered by the Grasshopper plugin Kangaroo and Finite Element software DIANA.
The research shows - via its design rules – that a hybrid facetted shell bridge, consisting of glass facets and FRP joints is the most efficient variant. A concave shape is chosen for its “natural” parapet and relatively low share of bending stress in the total stress, while still measuring up to the bridges’ requirements. The concave shape is tessellated with triangular panels due to problems with the – in theory – more efficient hexagonal panels. By shortening the length of connections along each side of a triangular panel, the behavior of hexagonal panels is approximated. Several topologically different triangular tessellation variants have been analyzed using DIANA. The topological variant based on a combination of the equilateral and isosceles triangle proved to result in the lowest stress and deformation values under NEN-based loads and is therefore the most efficient variant. By adding more curvature to the base of the bridge, better shell behavior is achieved, resulting in even lower stress and deformation values.
The connection between the panels is made using an FRP embedded sheet, which results in a higher axial stiffness and ultimately also a higher critical load of the bridge. The ideal thickness of this sheet is determined with FEM analysis. A clamped double-pin joint is chosen for its uniformity and adaptability. Finally, an uncertainty analysis is performed to investigate the influence of tolerance related production flaws on stress levels in the joint, which resulted in no issues.