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Fiber-reinforced polymers find increasing application in bridges

Fiber-reinforced polymers find increasing application in bridges

28-Apr-16

Fiber-reinforced polymer (FRP) has the potential to fulfil all needs. However, since the key to FRP’s structural properties comes from the fibers (stronger than steel) inside it, their orientation plays a major role. Unlike steel, which is homogenous, FRP is an engineered material. It always consists of structural fibers fixed in a matrix of thermoset resin. The material properties are a result of the type, amount and orientation of the fibers inside it. The fibers can be compared to the steel reinforcement in concrete: the reinforced bars are placed where they are most effective, and always come in multiple directions to ensure integrity. Safety is paramount, also in the case of unforeseen loading. By their nature, loading on infrastructural works is demanding: heavy loads and impacts, in many load-cycles. The impact not only comes from vibrations of the vehicles, but also from little stones stuck in the profiling of the tyres, and any unforeseen accidents that may occur. While FRP potentially has high capacity, it is the fiber-layout inside it, together with the fabrication method, that sets the real qualities. FRP is the material of choice to realise integrated detailing and architectural geometries. This was recently demonstrated in a series of projects, and for a very modest budget. In the infusion-technique that traffic-resistant InfraCore is based on, there is maximum freedom to shape the structure to the specific needs. This is different to construction based on standardised elements such as profiles. InfraCore was designed to combine resistance to heavy loading with full integrity against impacts. This technology was developed by FiberCore Europe over the course of 15 years, and has meanwhile been tested and applied in panel-like form in bridges, bridge decks and lock gates. At the heart is a three dimensionally designed fiber-layout. These fibers run not only in the longitudinal direction (as standard elements tend to do), but also in orthogonal- and transverse direction. This gives InfraCore its resistance, coherence and integrity in all directions. Coming back to the comparison with the reinforcement-layout in concrete: InfraCore is exactly that, but at a much more refined level, and at a much lower weight.
In the construction phase of the structure, many layers of glassfiber fabrics are shaped on a mould and around foam blocks. These blocks act as lost formwork only, but are the key to the shaping potential of creating special shapes. These could be curves and folds, varying cambers and non-constant cross-sections. For its new range of bridges, the city of Rotterdam choose for long-lasting FRP, all built with the InfraCore-technology.  The design potential of FRP and the infusion technique came to full strength here. The geometrical variations could be handled within the system’s variables without requiring costly interventions. In another project, the traditional camber of a bridge was replaced by a sine-shaped wave.  Rotterdam  in The Netherlands has an extensive network of ageing wooden pedestrian and cyclist bridges. Instead of traditional wood or concrete and steel when erecting replacement bridges, plastic has become the preferred material. Since a plastic bridge can be installed in just a single day, it minimizes detours and other disruptions while saving time, money and resources. Plastic composite-based bridges offer exceptional longevity and are relatively low-maintenance compared to conventional building materials. Repairs and routine upkeep are rather easy while the need for total replacement every couple of decades is almost null, as FRP bridges last for almost a 100 years. 

An ageing bridge over River Thames has been replaced with bridge made with Fiber Reinforced Polymer. The UK Environment Agency commissioned ECS Engineering Services to replace its ageing bridge at its site at Mapledurham on the River Thames, and design, supply and install a new bridge. To ensure the new bridge would last decades with minimal maintenance, ECS used Infracore. Although Fibrecore has built more than 450 bridges installed across mainland Europe, an FRP approach to bridge building is relatively new in the UK. ECS had two major goals for the project: to improve the capacity of the local access routes to the Mapledurham weir and upgrade the size and strength of the existing bridge structure. To accomplish both, ECS needed a material that would help it combat the challenges involved in replacing the bridge – such as the remote site location, limited vehicle access and short time frames required for installation. The FRP technology, combined with an off-site manufacturing approach, allowed for the composite bridge deck to be constructed and delivered in a short period of time. The use of a lightweight Infracore FRP deck meant that ECS was able to deliver the bridge to site by floating it on a barge down the Thames. The installation itself was relatively straightforward, with site preparation taking up a majority of the build time. Once the foundation preparation was completed and the new bridge was craned off the water, the actual installation was completed within a day – a key advantage in utilizing a pre-built bridge solution. According to ECS, the bridge deck itself is molded in a single piece, with an integrated bonded anti slip wearing surface. The FRP deck is custom manufactured to have the most efficient combination of strength and stiffness for the particular bridge span and loading required, which results in bridge decks that are around one-third the weight of steel or concrete equivalents. With no physical joints, and no exterior paint finish required, the bridge decks are maintenance free and are expected to have a service life in excess of 100 years.

A new bridge deck in Ohio has been made with fiber-reinforced polymer. Rotting timbers and corroding steel forced the National Park Service to close the Hillside Pedestrian Bridge in Ohio’s Cuyahoga Valley National Park. The Federal Highway Administration specified that fiber-reinforced polymer (FRP) material be used in the new deck. Composite Advantage won the bid to replace the structure with its FiberSPAN bridge deck system. Weathering steel, a new surface wear product and different color choices were some of the features that attracted the National Park Service to its FRP product says Composite Advantage President Scott Reeve. “We worked with the Federal Highway Administration in 2013 on the installation of a FiberSPAN bridge deck for a 3-span steel superstructure at Wolf Creek National Park near Vienna, Virginia,” he says. “Their experience with the product on that job influenced their decision to include FRP in the design for the Hillside Pedestrian Bridge project.” The FiberSPAN bridge deck with attached curbs was installed in March 2016 on a new substructure comprised of weathering steel stringers. Ten FRP panels were attached with stainless steel connection clips. With a live load rating of 90 psf and a maintenance vehicle loading of H-5, the large prefabricated panels eliminated the man-hours typically associated with assembly of multiple smaller components and tasks such as pouring concrete. The deck with its Matacryl quartz aggregate wear surface weighs 7 lbs per square inch. To address the corrosion issues previously associated with Hillside’s steel superstructure, high elongation sealant was applied to panel-to-panel joints. Drainage scuppers were also added to select deck panels. The color teak was chosen for deck and wear surface to match the color of the weathering steel and make rust stains from the steel less noticeable over time.

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