PORR ProjectsWorld of PORR 160/2012

Stefan Plankensteiner

IntroductionThe “Ötztaler Achbrücke” is a single-track railway bridge inthe Austrian province of Tyrol. Owned by ÖBB, the AustrianFederal Rail System, it forms part of the rail connectionbetween the stations Ötztal and Imst, crossing the stream thatruns along the Ötz valley (Ötztaler Ache) close to where theAche flows into the river Inn. The first, 121 m-long bridge atthis site was built in 1883; in 1968, the original trussconstruction was replaced by a 280-t steel hollow box girder.The level three-span bridge crosses the valley floor at aheight of approx. 23 m. The first of the three spans isdesigned as a single-span girder. The other two spans arebridged by a through girder. The two piers are founded oneither side of the stream, outside its normal flow cross-section.

The steel structure of the bridge required a great deal ofmaintenance and, due to insufficient durability of the jointsand fastenings, major repair works were necessary on anongoing basis. Because of this situation, trains could onlypass the bridge at speeds of around 40 km/h, which in effectmeant that express trains regularly lost two minutes of traveltime on this part of the line. Moreover, the noise levels wereno longer acceptable.

Old “Ötztaler Achbrücke” bridge (2010)Image: PORR

ÖBB Infrastruktur AG, the rail infrastructure subsidiary ofÖBB, finally decided to hold a competition, inviting bidders tosubmit variant analyses with regard to different structuralsystem and architectural design options. As a result of thecompetition, ÖBB eventually decided not to rehabilitate theexisting structure, but to have a new bridge built, as this wasthe most economical solution for the single-track line. Thenew bridge, which boasts extraordinary design features, issited parallel to and 10 to 14 m away from the old one.

The projectThe new three-span bridge with span lengths of 42 m, 60.6 mand another 42 m has a composite structure with a steelhollow box girder and in-situ concrete deck. A special featureis that the steel box girder is rigid-jointed to the piers, so thatno bearings (which are high-maintenance, with frequent needfor inspections) were required on the pier heads. Acontinuous ballast bed was placed on top of the new load-bearing structure. This homogenous superstructure improvesthe track quality for driving, while at the same time reducingnoise emissions.

The variant analyses had shown that building a new bridgealongside the old one was a better solution, both technicallyand economically, than replacing the load-bearing structure ofthe existing one. Moving the track’s axis to the north had theadded advantage of widening the curve on the connectingline towards the city of Innsbruck, adding about 10 km/h topermissible train travel speed on this section of the line. Thelayout of the rail route was modified over a length of 700 mand sited so that it will be possible to build a second single-track bridge structure south of the existing one, should the railline be upgraded to twin-track operation at some point in thefuture.

The contractIn November 2010, the relevant ÖBB branch (ÖBB-Infrastruktur Aktiengesellschaft – GB Strecken- undBahnhofsmanagement Region West) awarded the contract forthe demolition of the “venerable” Ötztaler Achbrücke railwaybridge and construction of a 145 m-long and 16 m-wide steelbridge, plus all required groundwork, drainage and foundationworks, to the Tyrol branch of TEERAG-ASDAG AG. After athorough examination of the site and probing for potentiallydangerous war relics in the autumn of 2010, the demandingwork on this impressive project began in January 2011. Thenew bridge was opened for rail operation on time, on 21stAugust 2011. Over the following months, the old bridge wasdemolished, and the temporary bridge that had been usedduring construction was removed, as was the now redundantrailway embankment. After the necessary road construction,landscaping and other finishing works had been completed,the project was concluded in the spring of 2012.

Foundation and substructureAt the start of the works, a temporary bridge structure had tobe erected to provide access to all parts of the site, includingthe eastern abutment on the Innsbruck side, across theÖtztaler Ache. As soon as this and the necessary site accessroads were in place, groundwork started on the Innsbruckabutment to prepare the construction and assembly site. Thesite around the other abutment on the Bludenz side wasprepared at the same time, independently of the erection ofthe temporary bridge.

New construction replaces Achbrücke railwaybridge, TyrolElegant bridge design benefits rail passengers too

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PORR ProjectsWorld of PORR 160/2012

The foundation of the bridge consists of 24 large-diameterbored piles (diameter 120 cm), arranged in two rows. Thepiles are up to 20 m long and were placed at an angle, withthe pile heads bonded to massive reinforced concrete slabswhich are up to 2.5 m thick. To allow access for inspection ofthe hollow box girder in the course of future maintenanceworks, the abutment on the Innsbruck side was built with aninterior staircase. Both the Innsbruck and Bludenz abutmentsare founded on four slanted large-diameter piles. The twopiers are approximately 16 m high and located close to theriver banks. They are designed with hexagonal cross-sectionsabove the pile head slabs and rectangular cross-sections atthe lower end of the superstructure. Rising from the slabs inconical shape, the piers taper to an inflection point about 4.3m below the bottom of the superstructure. The architecturaldesign of the massive piers involved complex shuttering andreinforcement work, which together with sometimes freezingtemperatures posed a major challenge to the workers.

Driving of piles and formwork for pier concretingImage: PORR

Reinforcement and formwork for pier on Bludenz sideImage: PORR

Reinforcement and formwork for pier on Bludenz sideImage: PORR

Structural design – steel frame – steel-concretecomposite structureThe 145.6 m-long superstructure of the bridge was designed

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PORR ProjectsWorld of PORR 160/2012

as a three-span steel and concrete composite structure basedon a torsion-proof hollow box. The finished height of thestructure is 1.9 m at the abutments and about 3.1 m at thepier heads, plus up to 100 mm-thick metal plates (web andchord plates). The arched beams and narrow steel structure(lower chord: 2.6 m, upper chord: 3.8 m) lend the bridge anelegant, light-weight appearance. The steel structure is rigid-jointed to the pier heads by means of a “cappingconstruction”. This consists of two 40-mm vertical metalplates on the sides, which were welded onto the massive, 100mm-thick lower chord plate of the steel structure on the oneside; on the other side, they are fixed to the pier head usingsome 2,400 shear connectors. These steel elements wereembedded in the concrete when the piers were cast.

The hollow steel girder has a total weight of 510 tonnes. Itwas produced at the steel workshop in nine individualsegments which were delivered by heavy transport vehicles.An added difficulty was that access to the site was partly overunpaved roads. Having arrived at the prepared on-siteassembly areas, the segments were pre-assembled andwelded together to form six bridge sections, each of whichwas up to 34 m long and weighed up to 100 tonnes. The steelstructure sections were then lifted one by one onto the pierheads, abutments and temporary frames by one of thebiggest caterpillar cranes in Austria. With a maximum heightof 140 m and a weight of 960 tonnes, the lattice boom crane(Liebherr model LR 1600) can lift loads of up to 600 tonnes.Its imposing shape was visible from a considerable distancearound the construction site. The steelwork was completedwith the welding together of the girder sections. The entiresteel structure was put in place within an ambitiouslyscheduled period of only about three weeks.

Aerial view of the steel structure in April 2011Image: PORR

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PORR ProjectsWorld of PORR 160/2012

Positioning of the central section of the hollow steel boxImage: PORR

Meanwhile, erection of the complex falsework and formwork(travelling formwork) for the 6.5 m-wide reinforced in-situconcrete deck slab had already begun. Reinforcing andconcreting were carried out in five sections (26.5 – 31.2 m),applying a “step-and-backstep” process.

Preparing the steel-concrete composite structureImage: PORR

Travelling formwork for the composite structure, central section of thebridgeImage: PORR

Finishing worksThis was followed by the finishing works, including installationof the track transition sections and drainage outlets, sealingof the load-bearing structure and application of the protectiveasphalt cover, placement of the precast side beams withintegrated cable troughs, installation of the bridge railings,etc. During an operational shutdown from 5th to 21st August2011, which had been scheduled well ahead, groundworkand superstructure completion works (which lasted only 48hours) were carried out in the transition zones; the continuousballast bed and tracks were put in place, including additionalfinishing works (overhead contact line, etc.). After the workshad been duly completed as scheduled, the bridge was load-tested on 21st August 2011. Three ÖBB locomotives of the1044 series with a total weight of about 260 tonnes wereused in the trial. Immediately after the strain measurements,the first regular ÖBB Railjet train crossed the new bridge at aspeed of 80 km/h.

Completion of the new Ötztaler Achbrücke bridge in August 2011Image: PORR

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PORR ProjectsWorld of PORR 160/2012

Load-bearing structure and track deck, view towards westImage: PORR

Demolition of old bridge – final work stagesThe steel structure of the old bridge was removed on 8thNovember 2011. The method used was simple: on the pierheads and abutments, the 230-t steel structure was slowlypushed sideways in a controlled movement until it toppledover the edge and fell down in one piece, hitting the groundbelow after a 120-m fall. The steel structure was then dismantled in an orderly processand the scrap reclaimed for reuse. The piers and abutmentswere demolished by blasting as well as conventional cutting.In the autumn of 2011, the revetment of the banks wasreconstituted, the temporary bridge was dismantled, and theold railway embankments, which were no longer needed,were removed. Landscaping and replanting, road constructionand finishing works concluded the project in spring 2012.

ConclusionThe project posed major challenges for the constructioncompany TEERAG-ASDAG AG (Tyrol branch), the sub-contractor responsible for the steel structure, the designingengineers and the local construction supervisors. These weredue to the technical complexity of the construction anderection of the bridge, the short construction period of onlyeight months and the fact that rail traffic on the line had tocontinue nearly uninterrupted throughout the wholeconstruction period. Moreover, the local site conditions(access roads) were difficult, and special consideration had tobe given to the fact that the site is located in a natureconservation area (“Bergsturz Tschirgant” area). With thisproject, TEERAG-ASDAG AG, an important division of thePORR group, furnished ample proof of its ability tosuccessfully carry out complex infrastructure projects to shortdeadlines.

The hollow box girder and one pier seen from belowImage: PORR

With the new “Ötztaler Achbrücke” in place, the speedrestriction (40 km/h) has become a thing of the past. The newstructure has brought significant improvements for railpassengers. For them, it means less noise, punctual trainservices, a stable timetable and greater overall reliability ofthe local transport infrastructure. With its aestheticallypleasing, elegant design, the bridge is a railway engineeringlandmark. Positioned at the entry to the Ötztal valley, it is setin an impressive landscape and blends harmoniously into thesurrounding nature conservation zone.

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PORR ProjectsWorld of PORR 160/2012

Project data

Client ÖBB Infrastruktur AG,Innsbruck

Contractor TEERAG-ASDAG AGTyrol branch

Length of contractsection

800 m

Bridge length 145 m

Bridge width 7.06 m

Bridge surface 950 m²

Span widths 42 m – 60.6 m – 42 m

Pier height 16 m

Steel structure 510 t

Concrete 1,500 m³

Reinforcing steel 390 t

Bored piles 450 m

Embankment filling 12,000 m³

Start of construction January 2011

Start of rail operation 21st August 2011

Demolition of old bridge November 2011

Completion of project Spring 2012

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