The PreCoBeam solution
This economical construction method consisted of two rolled sections separated along their web, which were connected via composite dowels to a concrete deck of varying height. When the height of the prefabricated steel section is higher than the concrete deck, it is called a T-shaped external reinforcement – this was used in the construction of the bridge. The superstructure consisted of two prefabricated steel beams with external reinforcement that were complemented with an in situ concrete deck after assembly.
Placed next to each other, the beams allow for a deck width of 3.5 m with caps on both sides measuring 0.75 m. The construction height in the centre of bridge is 0.7 m and 1.4 m at the bearings. The abutment foundations were realised as deep foundations with five bored piles each with a diameter of 90 cm and a length of 7.5 m. The construction was carried out in accordance with the German technical regulation DIBt Z-26.4-56, which applies specifically to this type of construction.The construction work connected with implementing the first phase of the investment commenced in March 2011. The section of road being reconstructed and expanded is around 890 metres in length.
In order to minimise damage to the steel beams’ corrosion protection, a resistant hot-dip galvanising process was utilised instead of an organic coating. Current research has shown that this will ensure that the corrosion protection will last for the whole service life of the bridge, which is designed to be 100 years.
In order to avoid maintenance and repair costs at a later stage, the aim was to use hot-dip galvanised steel beams for the PreCoBeam construction. The external reinforcement was made of two rolled sections of HD320x300 in steel grade S355 ML with a length of 20.38 m each.
When selecting the steel, the option to galvanise was key. Commonly, this is done by complying with the following specifications for silicon and phosphorous content: 0.14% ≤ Si ≤ 0.35% and P ≤ 0.035%. Additionally, the aluminium content should be limited to under 0.03%. Rolled sections from ArcelorMittal Europe – Long Products most commonly fulfil these requirements.