Construction of New Bridge in Mutters — World of PORR
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World of PORR 171/2017 PORR Projects Construction of new bridge in Mutters Railway bridge over the Mühlbachgraben Daniel Sebö new Mutters bridge over the Mühlbachgraben. Narrow access roads and very little space were among the biggest Project data challenges of the project. The location of the construction site in a stream bed did not make matters easier for the PORR Client Innsbrucker Verkehrsbetriebe und Stubaitalbahn GmbH specialists. Contractors PORR Bau GmbH Background Project type Infrastructure . Bridge construction The Stubaitalbahn railway was opened in 1904 and leads Project Construction of the new steel composite from Innsbruck to Fulpmes. The single-track branch line with scope bridge including renewal of the entire track a gauge of 1,000 mm has a total length of 18 km and runs superstructure and track substructure in the construction project along a gravel bed with wooden sleepers. The maximum longitudinal inclination of the track is 55 ‰, the smallest arc Construction September 2016 radius is 35 m. start The client decided on the construction of a new Construction November 2017 Mühlbachgraben bridge in Mutters, because refurbishment of end the area in the immediate vicinity of the 100-year-old listed Country Austria bridge and the pending refurbishment of the Mutter tunnel immediately adjacent to the bridge would have been just as expensive but less efficient. The new bridge is approximately 153 m long and 43 m high and passes across the Mühlbachgraben in front of the Mutters Tunnel with a slight left turn. The old bridge will be preserved and used in future as a pedestrian and bicycle bridge. The project The new construction also changes the course of the Stubaitalbahn railway. The new route is straightened and shortened, it deviates from the existing route at the 7,927 km route mark and returns to the existing track route at the 8,151 km route mark. Subsequently, the track will be adapted over a length of about 261 m. The narrow existing radii of the left Visualisation of the new bridge across the Mühlbachgraben in Tyrol. and the right arc in the track section will both be widened, Image: IVB Innsbruck resulting in a slight deviation from the existing track. The height progression of the new railway track is designed with a constant gradient of 50.03 ‰. This necessitated cutting through existing terrain for the Fulpmes-side abutment. The new track in this area passes over a reinforced concrete tub construction, which merges with a supporting construction to the right and left of the track. Foundation work and substructure For the deep foundation of the bridge piers, an incision had to be made into the steep terrain and secured with jetcrete and IBO anchors. Due to the spatial circumstances, the erected jetcrete shell was up to 10.0 m high. Aerial photo of the bridge construction shortly before completion in the middle of the image. Behind it is the old bridge, which will still be used by pedestrians and cyclists. Image: PORR AG General information In the autumn of 2016, following a public tender by the Innsbrucker Verkehrsbetriebe und Stubaitalbahn GmbH, PORR Bau GmbH was awarded the contract as general contractor for the construction of the Page 1 World of PORR 171/2017 PORR Projects and delivered to the construction site via special transports. The unique features of the bridge superstructure are the longitudinal gradient of 5 % and the radius of 88.0 m. The spans are 41.10 m, 48.50 m and 63.05 m. The superstructure also has a super-elevation of 150 mm at the centre of the main field. The steel pile sections were assembled using a 750 metric tonne crawler crane, which was transported to the construction site in pieces in a total of 52 lorry journeys. This 100 m high Liebherr LR 1750 lattice boom crane has a maximum lifting capacity of 600 metric tonnes and was an imposing presence on the site. To create a sufficiently large footprint for the crawler crane, the Mühlgrabenbach was provisionally filled in here too. Bored pile foundation, pier 2 Image: PORR AG Beneath the bridge, three steel piles were always pre- The foundations of the bridge structure were formed using 36 assembled, combined and then moved by the crawler crane. large bored piles with a diameter of 1.2 m and a length of 25.0 The entire superstructure was then lifted up to 35 m in five m, which were anchored up to 2.0 m deep into the rock. The hoists. The lifting weight varied from 77 metric tonnes with a bored piles were incorporated into two pile caps with a total payload length of 73.5 m to 183 metric tonnes with a payload cubage of 681 m³. The larger of the two pier foundations is length of 40.0 m. 14.0 m long, 11.0 m wide, and 2.45 m high. The 31 m piers are a special feature of the steel composite bridge. Their elliptical shape made the production of the formwork a special challenge. In order to produce the formwork with the tie hole layout in accordance with the tendering conditions, PORR, in cooperation with Doka, developed a special formwork solution with matrix formwork in exposed concrete grade SB3. Each pier was built in six concrete sections at a height of 5.40 m. Only the last pier section is 2.70 m high. In this section, the insert for the rigid connection was installed in the steel superstructure. Due to the height of the piers, a 250 metric tonne crane was deployed to move the 11 metric tonne insert. Due to the forces of the bridge acting on the insert, the reinforcement content was greatest in the last section, at Hoist no. 3 with steel construction piles 3, 4 and 5 at 182.6 metric tonnes. about 260 kg/m³. For this reason, in the connection area of Image: PORR AG the insert, the reinforcement was guided in two rows with a double layer of reinforcing steel with a diameter of 26 mm. As a result, placing the steel insert with 1,200 shear studs was a big challenge for the fitters. Abutment For the foundation of the bridge's bearing bank, GEWI anchors with a diameter of 63 mm were used for the deep foundations. The topographically difficult terrain placed severe limits on accessibility, so provisional earth deposits had to be made on the existing steep forest floor. This was the only way that the required construction equipment could be delivered and access the site for production of the Innsbruck abutment. Construction – steel bridge construction – composite Hoist no. 3 with steel construction piles 3, 4 and 5 at 182.6 metric tonnes. panel Image: PORR AG The 152.6 m steel superstructure is a three-layer composite construction in the shape of a torsionally rigid hollow box and consists of twelve individual pile sections and two end cross girders. These were manufactured in Carinthia Page 2 World of PORR 171/2017 PORR Projects Hoist no. 4 with steel construction pile 6 and 7 at 63 metric tonnes. The Steel superstructure before production of the composite panel. steel piles were assembled using a 100 m high lattice boom crane. Image: PORR AG Image: PORR AG Only 10 % of the individual lifting loads were diverted to the connecting structures (piles and abutments). The superstructure was only welded after it had been assembled with down-to-the-millimetre accuracy. The steel construction work was completed with the welding of the construction site joints of the steel box, especially the technically-demanding gap closure between the two piers. It was possible to start the formwork and reinforcement work while the last steel segments of the superstructure were being combined. The formwork system "ParaTopsystem" from Doka was used for this task. The 7.0 m-wide composite in-situ concrete slab was produced in five concrete sections with a total cubage of 374 m³. Production of the composite panel of the bridge superstructure. Image: PORR AG Hoist no. 4 with steel construction piles 6 and 7 at 63 metric tonnes. Image: PORR AG Page 3 World of PORR 171/2017 PORR Projects Construction progress of bridge and trough in September 2017. Image: PORR AG Aerial image of bridge and trough in September 2017. Image: PORR AG Production of the composite panel of the bridge superstructure. Facts and figures Image: PORR AG Project length 575.6 m A window of eight weeks Bridge surface 1,100 m² All work on the open track and the completion / finishing work Bridge length 153 m on the bridge superstructure and the trough structure Steel construction 510 metric tonnes connecting to the Fulpmes-side abutment had to be carried out over the course of an eight-week track possession period. Concrete cubage 4,106 m³ In addition, a retaining wall was erected with a length of 67.50 Reinforced concrete 515 metric tonnes m and a mean height of 3.50 m in exposed concrete grade Large bored piles dm 120 cm 925 m SB2 with formwork matrices in a natural stone look and the entire substructure and the track itself were renewed in the Jetcrete surface 1,011 m² construction project. The track construction work was carried IBO anchors 4,505 m out within the group by the Bahnbau/Gleisbau (railway Micro-piles 1,160 m construction/track construction) department. Earth excavated/moved 8,750 m³ Summary This project enabled PORR to demonstrate its impressive experience and competence in infrastructure and bridge construction. The biggest challenges in the construction of the new bridge were the confined space, the topographical location of the construction site in a stream gulley and the difficult access.