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With pre-cast concrete girders in composite construction, we are able to build the structure in a short window of time at consistent top quality, something which is also an important cost factor in the end
Commissioned by Hessen Mobil, Kassel, the Kleffel engineering office for structural design is currently planning the replacement of a road bridge on the federal highway A7 between Flensburg and Füssen. The engineering office, from Rippershausen, Thuringia, specializes in demanding tasks as a structural planner in bridge construction – whether for steel, pre-stressed concrete, concrete composite or steel composite bridges. A wide range of engineering services is on offer: The portfolio runs from feasibility studies through pre-planning, design planning and structural planning to statics testing by Mr Kleffel Dipl.-Ing., tendering, site management and health and safety coordination.
For the creation of the concept for the replacement bridge, Hessen Mobil, responsible for the construction, contracted the HIG engineering office (Hensel Ingenieur GmbH) from Kassel. Here, the official design and demanding transport concept for the new building of a 6-lane bridge, was developed. Stefan Kleffel Dipl.-Ing. was glad to take on the special challenge of implementing the designed solution within the framework of detailed planning. The company Adolf Lupp GmbH & Co. KG from Nidda was tasked with the execution of the new construction and dismantling of the old.
Peter Strauß Dipl.-Ing. from the HIG engineering office was commissioned with the statics testing by the client.
As shown in figure 1, the new construction was already defined in the official design as being an integral, pre-stressed composite concrete bridge with a girder span of 27.61 meters and a width of 40.50 meters, to be built in 5 construction phases. The construction phases in this regard considered the need to demolish the existing rigid-frame bridge and build the new one (figure 2). It was not just the realization of the replacement bridge that took place during running operations: By requirement of the client, the traffic on the A7 was to run continuously and as far as possible unhindered during the demolition works.
The spatial model created for the bridge records the oblique-angled rigid-frame bridge as a folded plate structure on pile foundations (figure 3), representing the different construction phases with in total 13 static states of construction and 145 load states. Because of the ground conditions, the pile foundations beneath both abutments are asymmetrically arranged. The superstructure is formed of 2 x 8 pre-cast girders, manufactured by the construction company Adolf Lupp and pre-tensioned in pre-casting beds.
Here, the entire bridge is recorded in an integral overall model as 2 mutually independent partial structures with beams arranged lengthwise and an orthotropic, load-spreading carriageway running transversely. The pre-cast girders are elastically clamped in the bearing walls via the steel rod reinforcements.
The use of pre-cast girders in this task turns out not only to be technically sensible but also economic: It allows the avoidance of expensive support and protective structures. As the pre-fabrication of the superstructure and the on-site creation of the substructure could be realized in parallel, the total building time could be notably shortened. The use of pre-cast girders also ensured effective quality assurance at the factory – a solid basis for high and consistent quality in execution. It is not for no reason that only in rare cases the transport routes passing underneath needed to be blocked. “With pre-cast concrete girders in composite construction, we were able to realize the structure in a short window of time at consistent top quality, something which was also an important cost factor in the end,” explains Stefan Kleffel, Dipl.-Ing.
Sub-components of the bridge are exposed to extreme stresses that are only present for a specific period in individual construction phases. This is particularly the case for the bored piles