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Rolled HISTAR® beams instead of welded girders: structural optimisation for a road bridge project in Poland
The construction of the Sucharski Route was part of the creation and modernisation of Gdańsk’s road system in 2007-2013 in order to connect the city with the national road network (A1 and S7) and part of the project of the European E75 and E77 routes in Poland. Optimisation of the steel structure solution involved collaboration between the general contractor SKANSKA S.A., the design agency EUROPROJEKT Gdańsk S.A, and the steel structure supplier ArcelorMittal. 2040 tonnes of ArcelorMittal's HISTAR® 460 steel was used.
The WD8 consists of two independent constructions (one for each carriageway) of 10.6 m wide and around 390 m long. It has 11 spans, the central span measuring 40 m and the lateral ones 25 m. The WD7 is shorter, with a length of about 170 m, but the structure is wider - 11.2 m across. It is a 5-span bridge with span lengths of 30-40 m. The height of the deck above the ground surface is approximately 12 m in the centre of viaduct WD7. Both objects are built with continuous beams and have foundations in the form of poles of a diameter of 1.5 m and lengths of 22-32 m.
The bridges take the road over railway lines and local roads and were designed as plain girder VFT (Prefabricated Composite Construction Method) objects in S355 steel grade with slenderness ratios 25-28. With the surface covering over a hectare, the choice of technology was of key importance from a technical and economic point of view. Due to the ground conditions and obstacles in the form of railway lines, a central span of approximately 40 m was decided upon along with a complex transversal structure made from prefabricated elements as being a more effective solution than pre-stressed.
Replacement project: HISTAR® rolled beams instead of S355 steel welded girders
Instead of the S355 steel welded girders, it was decided to use HISTAR® 460 rolled steel beams, which led to the creation of Poland’s first objects using VFT technology with rolled sections in this steel grade. At the same time the WD8, with nearly 400 m of length, is the longest VFT object in the country.
There were several factors suggesting it would be more beneficial to use HISTAR® 460 rolled sections rather than welded S355 steel girders. Rolled beams enable tonnage reduction by around 10% or even more when optimisation of the finishing of individual beams is envisaged in an object.
The sections delivered to the construction site were 41 m long, eliminating the need for any welding on site. The total amount of welding was reduced by 80%. Using rolled beams ensures a long fatigue life for an object, which is why static schemes in the form of frames or beams from continuous S460 steel is justified from a technical and economic point of view. The rolled sections are characterised by a smaller surface than welded plate girders – the surface for anti-corrosion protection divided by the mass of the structure is usually around 15-30% compared to welded plate girders (an advantage as far as maintenance is concerned).
For the requirements of this project, in June 2011 the Differdange plant in Luxembourg produced 137 beams of lengths between 25 and 41 m. These were HL1100 beams (the type of sections used for the construction of bridges). After adding the pre-cambering, the finishing involving welding the necessary reinforcing plates to the lower flange in the support area. The end plates, shear studs, and painting were also completed at the plant. This efficient action resulted in the first fully finished beams of the WD7 viaduct being delivered to Gdańsk in August 2011 (by rail to Gdańsk and then by road to the construction site).
The concrete transom solution
In the case of the WD7 and WD8, as with most VFT beam structures in Poland, the contractor decided to construct a prefabricated C40/50 concrete deck onto the steel beams before positioning them in the structure. The innovation of the WD7 and WD8 was the introduction of a staged process of completing the transoms, making assembly towers unnecessary at the supports.
Once the beams are positioned correctly, with the prefabricated deck forming a lost formwork for the in-situ deck, the concrete for the deck was poured on the slab. This way, the construction of the bridge deck was a simple process completed in three stages. First, the assembly of the prefabricated slab on top of the beam, which covers around a third of the concrete deck's total height and acts like a formwork for the concrete poured in the second stage. In the third stage, the finishing of the bridge deck was completed in the traditional manner.
The complex prefabricated structures were placed in their intended location using a crane, and their mass reached 50 tonnes. The individual spans were completed in one week on average.
The bridge deck and transoms are made of C35/45 concrete. The span structure was completed in June 2013, and the objects were opened to traffic in October 2013.
- 2007 - 2013
- Engineering office:
EUROPROJEKT Gdańsk S.A.
Spółka Gdańskie Inwestycje Komunalne Sp. z o.o.
SKANSKA S.A. (general contractor)
ArcelorMittal (steel structure)
mat. Gdańskie Inwestycje Komunalne, ArcelorMittal
Riccardo ZANON, Oliver HECHLER, Wojciech OCHOJSKI– ArcelorMittal Long Carbon Europe
Paweł Klimaszewski - EUROPROJEKT
Wojciech Lorenc – Politechnika Wrocławska