Doka delivers cantilevering for super-slim piers at Lahntal Bridge
First publishedin World Highways
Pairs of super-slim circular reinforced columns carry the superstructure. The diameter is no more than 2.80m at the widest and the highest piers are 57.0m tall
Doka’s formwork expertise is currently in demand during the construction of one of the busiest motorway viaducts in Germany
The 400m six-lane Lahntal Bridge in Limburg dates from the early 1960s. Every day about 100,000 vehicles cross the bridge that spans the valley of the River Lahn. But traffic loads have increased sharply, so a new bridge is being built sited just a few metres west of the old viaduct.
The new Lahntal viaduct will measure a massive 43.5m in width, enabling eight lanes plus hard shoulders; the old motorway bridge had no hard shoulders.
Work started in September 2013, with the new bridge opening to traffic in Autumn 2016 and the final demolition work set for completion at the end of 2017. The project is funded by Germany's federal government at a cost of nearly €93 million. The old bridge will be fully demolished by autumn 2017.
The 450m-long beam bridge is a design by the joint venture of Bürogemeinschaft Konstruktionsgruppe Bauen from Kempten and Munich-based architects Architekturbüro Karl + Probst. The roadways are 62m above the lowest point of the valley floor and the seven spans range in length from 45-90m in length. No bridge pier has had to be situated in the waters of the River Lahn.
Haunched, twin-cell pre-stressed concrete box girders form the superstructures. Pairs of super-slim, circular reinforced concrete columns will transfer the loads of the bridge. Maximum pier diameter is a mere 2.8m and the tallest piers stand 57m. The cantilevering method is used to construct the superstructures. Secondary pier structures provide additional stability for the build phase. Lead contractor is Max Bögl Stiftung & Co. KG and Doka was awarded the contract for the extensive formwork.
Climbing-system technology Automatic climbing formwork Xclimb 60 is used to build the circular-section columns of the primary piers. The system climbs hydraulically and is anchored to the structure at all times by guiding shoes, meaning that it can climb even when wind speeds are as high as 72km/h.
A closed workspace flat measuring 340m² for the pier-head formwork is poised 50m above the valley floor. Doka's pre-assembly on site took care of the entire pre-assembly process
The formwork itself is made up of large-area formwork Top 50 planned specifically for this project. The panels consist of timber formwork beams H20 top and steel walings WU14. Maximum pouring height is 5.75m at a formwork height of up to 6m. Ladder systems XS with cages ensure safe up-and-down access between the three platform levels.
Workspace flat measuring 340m² Asymmetric pier heads are the springers for cantilever construction. The pier heads are constructed on top of each pair of primary piers and are anchored into the adjacent pair of secondary piers. There are 675m³ of concrete in each pier head. This corresponds to a concrete self-weight of just under 1,700tonnes. Plus the weight of the reinforcement and the weight of the formwork. The pier heads are poured in three casting steps. The heavy steel structure used is 90% Doka rental material. The entire formwork solution for the pier heads plus falsework came from Doka, so everything was from a single source.
Two Primary beams, HEB 1000 each 20m long, are the basis of each pier-head formwork structure. The secondary beams are 10 coupled anchoring cross beam CFT (concrete filled steel tube). Together they carry a closed workspace flat measuring 340m² poised at heights up to 50m above the valley floor.
Pre-assembly of the bottom formwork units and the all-round guardrail systems was handled by Doka’s pre-assembly service on site. The team also takes care of installation and removal of the eight steel-girder grilles.
Formwork for the circular-section primary piers climbs with automatic climbing formwork Xclimb 60. Guiding shoes hold the system locked against the structure at all times
The bottom slab is the first construction section of the pier head. It has a self-weight of 437.5tonnes and during its construction the steel-girder grilles slowly drop about 10cm. This had to be taken into account in planning and construction. The bottom slab subsequently carries the weight of the second and third construction sections.
The project owner had drawn up a set of detailed requirements for facing-board patterning, joins and visible finish of the pier heads. The facing boards for each of the eight pier heads were set by site. Doka supplied the necessary planning and the material for two formwork sets, each consisting of 950m² of project-specific Top 50 beam grills. Comprehensive fall-protection systems were also needed at the exposed platform ends for the second and third concreting sections.
Secondary piers for added stability The superstructures of the new Lahntal viaduct are constructed toward each other from pier head to pier head. The cantilever forming travellers work in pairs, so that the horizontal forces acting on the bridge piers are always in equilibrium. Each pair of primary piers has two adjacent secondary piers. They stabilise the pier head at all times while cantilevering is in progress. The secondary piers have a cross-section of 2mx2m and they are up to 50m high. Lead contractor Bögl used its own slipform formwork to erect these stabilising structures.
The monolithic pier heads of the secondary piers have an integral pier reinforcement consisting of steel beams. These pier heads were formed with two sets of framed formwork Framax Xlife. Eight sets of working platforms provided the all-important workplace safety. They are used as the work-deck level and as set-down areas for additional working scaffolds for the construction and subsequent dismantling of the secondary pier heads.
Cantilevering is the construction method for the haunched, twin-cell pre-stressed box girders of the superstructure
Cantilever forming travellers
The cantilever forming travellers on the Lahntal viaduct each have four longitudinal trusses. They can handle varying section lengths from 3.75-5m and concrete weights up to 250 tonnes. Complete with platforms the bottom grid is 9.5m wide and 25m long. With formwork and platforms, each of the four cantilever forming travellers weighs around 130tonnes. Initial assembly of all the cantilever forming travellers was by Doka’s on-site pre-assembly team.
A total of 12 complete repositionings of the cantilever forming travellers had to be handled as well. Doka designed and built a special strand-jack platform using the Bögl company's own materials for cantilevering. This platform was used to hoist the bottom grids straight off the ground without the assistance of heavy-duty truck-mounted cranes.
Through to the closing cycle, there is a 1.25m height variance at the bottom of the bridge's cross-section. So the bottom formwork telescopes in the area of the webs to allow for this difference. The inside formwork for the trough consists of a drawer structure for speedy repositioning. All the formwork elements come from the large-area formwork Top 50 modular 'building block' system. Fully integrated platform systems ensure safety at work.
When the cantilever forming traveller advances, an articulated carrier system automatically adjusts the bottom grid.
Unlike typical cycles, the closing cycle has to be cast in two concreting sections. The bottom and the web are cast first. The top-slab rails of the cantilever forming traveller are then extended without any prior dismantling. The concrete is then cast for the roadway slab.
When the closing cycle is completed, the cantilever forming carriage is brought back into position above the axis of the piers. Special retractors next come into play. With the carriage back at the piers, the bottom grid can be lowered. The carriage is then stripped down into big, largely undismantled repositioning units. Even the anchoring cross beams, more than 24m long, remain in place complete with the platform. At night, massive heavy-duty haulers manoeuvre the units into position for work on the other carriageway of the new bridge.
Who’s who at the Lahntal Bridge, Limburg
| PROJECT: |
| Lahntal bridge, Limburg, Germany |
| CONSTRUCTION START: |
| September 2013 |
| OPENING TO TRAFFIC: |
| Autumn 2016 |
| DESIGN: |
| Joint venture between Bürogemeinschaft Konstruktionsgruppe Bauen, Kempten and Architekturbüro Karl + Probst, Munich |
| CONSTRUCTION WORK BY: |
| Max Bögl Stiftung & Co. KG, Sengenthal |
| FORMWORK SYSTEMS: |
| Framed formwork Framax Xlife, Automatic climbing formwork Xclimb 60, Large-area formwork Top 50, Cantilever forming travellers, customised constructions |
| FORMWORK PLANNING: |
| Doka Applications Technology Department, Maisach (bridge piers, stair tower, pier heads, working platforms, cantilever forming travellers), Doka Competence Centre Bridges, Amstetten, Austria (Planning and statics Cantilever forming travellers) |
| FORMWORK PRE-ASSEMBLY: |
| Doka (initial assembly and repositioning of cantilever forming travellers, assembly and disassembly of the eight steel-girder grilles, pre-assembly of the bottom formwork units and the all-round guardrail systems) |
| STATICS, CLIMBING FORMWORK: |
| Suess Staller Schmitt Ingenieure, Gräfelfing |
| STATICS, STEEL-GIRDER GRILLES: |
| Ingenieurbüro für Bauwesen - Stefan Baur, Berlin |
| FORMWORK CO-ORDINATION: |
| Doka, Nuremberg Branch |