68 thema 22 130 4440 4440 4440 4440 4440 25 637 500 500 5% 5% The strongest UHPC bridge in the Netherlands 1 Durable pedestrian bridges have become one of the most important applications of ultra-high performance concrete (UHPC) in the Netherlands. In 2015 FDN engineering designed and built an UHPC pedestrian bridge called 'Zwaaikom', over a water channel in the city of Eindhoven, The Netherlands. This project has shown that UHPC can be competitive with other materials such as timber or composite for this specific application. The proposed bridge won an open tender thanks to its exceptional durability and attractive architecture, which fits into the surrounding. 2 thema The strongest UHPC bridge in the Netherlands 3 2017 69 1000 3800 3500 80 100 150 400 445 30 800 stirrups 10 x Ø12 280 660 Ø12 x Ø10/100 x 100 Ø10 x Ø10/100 x100 prestressing tendon 13 x 0.6'-150 mm 2 / 1860 15 100 Ø10 x Ø10/100 x100 15 105 80 21 hollow body of the girder UHPFRC C170/200 + steel bres Design The bridge, fully made of ultra-high performance concrete (UHPC) C175/190 class, has a total length of 25.60 m, a clear span of 21.40 m and a total width of 3.80 m. The bridge deck is only 400 mm high. This corresponds with the slenderness of 1/55. The cross-section of the bridge with a hollow girder box can be seen in figure 2. The hollow part is filled with polystyrene, which was used as a lost formwork during the production process. The average thickness of the cross-sectional walls is around 100 mm. The rib in the middle of the cross-section does not have a structural function. It is just for better control of concrete pouring in the bottom slab. Apart from having compressive strength higher than 175 MPa, UHPC contained steel fibres which made it very ductile. In order to fully utilize advantages of its high compressive strength, beside traditional reinforcement, pre-stressing is applied. The bridge deck was post-tensioned with five tendons (photo 12), each with 13 strands. The cross-section is hence subjected to the relative large compressive force (around 13 500 kN) resulting in large stresses (around 17 MPa). In order to accommodate the anchor system and withstand large split- ting forces, a solid end beam was designed at both ends. Additional reinforcement was applied in the bottom slab to avoid pull out of the ducts from concrete since the cover of the duct was only 30 mm. The railing elements were also made from UHPC, with a cubic compressive strength of 150 MPa. The railing has a bionic form with randomly distributed struts. (fig. 6). The railing does not contribute to the general load bearing capacity of the bridge, but it must still withstand several loads. Thanks to the high strength of the concrete, the railing struts are only 50 mm thick. The anchor bolt rails have a zinc protection against the corrosion. Material The concrete mixture contains large amount of binder (white Portland cement 52.5 with a rapid hardening process) and a high-quality calcinated aggregate (bauxite), with a grain size 0-6 mm. The water-cement ratio was 0.17. The proper hydration and thixotropic behaviour in the fresh state was assured by additives such as super-plasticizer and un-hydrated micro-silica. The biggest challenge was to reach the required creamy-beige colour of the concrete, because the natural colour of the UHPC is dark grey. This was This was achieved by using a combination of white Portland cement, microsilica and a corresponding mixture of the pigments. Therefore, an additional experiment- Jan Falbr FDN Engineering + Construction 1 UHPC pedestrian bridge 'Zwaaikom' in Eindhoven 2 Side view of the bridge 3 Cross section of the bridge deck 4 Longitudinal cross section of the anchor head 4 3 The strongest UHPC bridge in the Netherlands 3 2017 70 60 70 mortar C110/130 Ø 8 mmepoxymortar anchor bolt M12/8.8-75 mm + ring 37/13/3 mm anchor rails 165 welding 110 railing element deck Ø 14 mm 455 455 70 4440 R = 213 220 m 4419 70 1000 89.4° 0 3 5 -3 -5 5 10 15 20 time [s] acceleration [m/s 2] excitation from joggers limit h Fcd F z I fctd = fctd = ct c