100 Bridges for 100 Years – City of Rotterdam Trusts New Technology for Infrastructure Investment
Text: Florian Maier
In June 2013, the city of Rotterdam has inaugurated the first of a a series of 34 fibre reinforced polymer (FRP) bridges for pedestrians and cyclists. The aim of the project is to make the city’s infrastructure durable and sustainable. It also marks a mental shift: while FRP-bridges previously were considered “special products”, with a technology called “InfraCore Inside” used to build them they have become viable. Furthermore, the project shows that the technology is proven, and ready to be implemented in architecturally designed bridges.
Lightweight, maintenance-free and mouldable
For the replacement of a range of dilapidated bridges, the city of Rotterdam specified FRP because of their low self weight, their resistance to corrosion and de-icing salts and environmental impacts, the very low maintenance-requirements, and the design life of 100 years. Since the bridges are lightweight, the foundation is kept simple. So, the bridges are both, of low initial cost and total cost of ownership. During their life span, the bridges can be easily moved when the urban infrastructure is revised, while at the end of the service life the bridges are fully recyclable.
The first bridge that has been installed in the Beverwaard-area of Rotterdam now is the first of a series more than 30 to be built in 2013. The bridges are designed by Olaf Gipser and Vista Landschapsarchitectuur en Stedenbouw (landscaping and urban design).
The bridges for Rotterdam together form a family. Their design is characterized by the facetted underside at non-orthogonal angles. These features also appear in the steel railings. Length and width of the bridges varies, as does the assembly of the inclined and flat parts.
A systematic build-up method enabled a rational construction method. It is an industrial, prefabricated system that can be scaled to the dimensions and shape requirements per bridge. InfraCore Inside consists of stacking custom-cut formwork elements combined with glass fibre mats, acting as reinforcement. As in beams of concrete and steel, the top and bottom are structurally most effective, and that is where the fibres are concentrated. This build-up can be scaled and shaped, while preserving InfraCore’s intrinsic properties of strength, durability, sustainability and safety.
FRP – stronger than steel
The bridge for Rotterdam is made of FRP. Comprising both fibres and resin, it is a composite material where the combined material outperforms that of its constituents: loose fibres can only take tensile forces but no compression. When surrounded by cured resin, the fibres can take compression, tension and shear forces, while also giving bending strength.
The fibres used are continuous and tens of meters long and thinner than stitching yarn. The fibres are incredibly strong: at least ten times stronger than steel. Note that fibres used in concrete are only up to 10cm long. The fibres are mostly glass fibres for their favourable ratio between properties and cost, but also stronger and stiffer carbon fibres may be used.
This is however not as simple as it may appear to be as mixing materials of different stiffnesses affects the distribution of forces. Such design considerations require specialist knowledge and an in-depth understanding of the underlying material sciences. Finally, also an understanding of the processing is essential. Design & build is thus the best model for successful building in FRP.
Advantages of constructing in FRP
FRP is emerging as the material of choice for civil engineering structures: infrastructure managers are loving it because it offers peace of mind without the strain of maintenance budges, designers see opportunities to break free from conventional structural shapes imposed by standardization of the construction industry. Instead they can now do justice to the urban context specific. Last but not least, clients appreciate the fast construction and short time on-site.
InfraCore Inside was developed for traffic loading (Eurocode), as well as the concentrated loadings, impact and load cycles that go with it. Other than in bridges InfraCore Inside is already used in heavy-loaded traffic decks and lock gates.
Olaf Gipser Architects, in collaboration with Vista Landschapsarchitectuur en Stedenbouw, Architect, Landscape Architect
FiberCore Europe, bridge development
Aannemersbedrijf Wallaard Noordeloos B.V., main contractor, abutments and installation