Nemetschek Structural User Contest 2013

136 X2 Category 2: Civil Structures The footbridge is composed of three different structural materials. The main bearing structure and secondary bearing structure are designed as glue-laminated timber beams. Connecting members, anchoring seats and stability bracings are designed with structural steel. The complete supporting structure with foundations and pilots are designed as massive concrete structures. Architectural design The architectural design is based on a smooth curved structure with a natural look to fit in a natural environment. Terrain at each end will be raised to prevent the flooding of the cycling track and pedestrian walkway. Both end foundation blocks will be partially filled with earth to form a new embankment raised to a new flood protection height. The main span is divided into three smaller spans with two middle support pillars. These pillars will be placed beyond the main river stream on dry river bed. The bridge structure is designed as a U-type channel with two large main beams connected with smaller cross beams at the bottom and longitudinal secondary beams for attaching walking boards. Design of the structure and technical data Timber bearing structure Two main beams are used to bridge across all three spans. The cross-section dimensions of these beams are 24 x 160 cm. The middle span beams are curved beams because of the curved bridge design. Span sections are connected together with steel plates and a large number of bolts to assure a rigid connection. Hinge connections are used to attach the beams to concrete supports and steel sockets will be used because of the large height of the cross-sections, in order to gain stability and prevent overturning. The main beams are connected with smaller cross-beam dimensions of 20 x 22 cm and are placed approximately every 5.0 m. The connections of these beams are rigid. This is achieved with the usage of steel plates and a large number of bolts in each connection. These beams also provide stability that counters overturning. Secondary beams with dimensions of 16 x 16 cm are then placed on top of the cross beams at an 83 - 84 cm distance to ensure the bearing of the final walking surface. The secondary beams are attached with hinge connections. All the beams are made as glue-laminated beams with Gl28h grade quality. Steel elements of the structure Besides the steel plates for all the connections and anchoring seats, steel bracing diagonals were used to achieve the global stability of the structure. These diagonal bracings are placed in intersections of cross beams and main beams and are attached through steel plates on the socket connections of the cross beams. All the diagonals have a strain link to gain the correct tension of the elements. Some diagonal bracing elements must be anchored to concrete supports to assure the global stability of the structure. Concrete foundations and pillars Both end foundation blocks are designed as concrete U-wall element blocks on strip foundations. The walls of the foundation blocks are 50 - 60 cm thick. On each front wall there are two raised concrete seats for the timber beams of the main bearing structure. Both rebar and mesh reinforcement were used for the adequate reinforcement of cross-sections. The middle pillars are slightly different, being made as walls with two inclined arms. Each inclined arm has a seat for the main timber beam on top. The walls of the middle pillars are anchored to a massive concrete girder on two pilots, which are drilled 5 - 6 m deep in bedrock. Software and calculation model Scia Engineer 2012 was chosen for the complete 3D-Modeling and for the calculation because there were three different structural materials in interaction. Some calculations were also “handmade”, such as for the timber section design because of complex vertical and horizontal frequencies that had to be calculated to prevent uncomfortable vibrations. The concrete design and reinforcement was carried out in cooperation with another engineering bureau with Nemetschek Allplan software. Some details for connections were also “handmade” and transferred into the computer design. Software: Allplan Engineering, Scia Engineer Wooden Footbridge with a Cycling Track Across the River “Sava” - Bohinjska Bistrica, Slovenia