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Exposed to increasing loads and rising traffic volumes, the condition of many bridges in Germany is currently undergoing review and recalculation, with assessments often revealing load deficits. In comparison to smaller structures, the replacement of large-scale bridges across the Rhine has proved to be very costly and raises questions regarding the economic and carbon costs of preserving listed assets.
Arup is using innovative digital tools to analyse a range of scenarios and details individually in order to safeguard the existing structure. Digitalisation can help future-proof historical infrastructure and balance the CO2 costs, while remaining a cost-effective solution for local government and highway agencies.
Take for example the Friedrich Ebert Bridge in Duisburg. The four-lane, cable-stayed bridge over the Rhine connects the districts of Ruhrort and Homberg. Originally built in 1956 as a self-anchored suspension bridge with a main span of 285m, it was initially strengthed in 1999. To ensure long-term safety, the city of Duisburg commissioned Arup to understand the load-bearing capacity of this imposing structure.
“On projects like this, conventional structural analysis do not provide sufficiently accurate data and would consequently favour a new replacement construction. The use of digital tools enables a more targeted analysis and thus economic strengthening measures in order to preserve the bridge. ”
Guillermo Munoz-Cobo Cique Senior Engineer at Arup
For example, the distribution of stresses in the main girders of the Friedrich Ebert Bridge depends directly on the considered cross-section, which in turn relies on the effective width taken into account. For cable-stayed bridges, where steel orthotropic plates are typically used, the effective width under permanent loads differs from that under live loads. In the past, grillage models were used, where the effective width was calculated based on the permanent loads condition. However this does not necessarily correspond to the reality. Only a detailed modelling of the deck by means of shell elements can provide realistic results.
As a result, we decided to develop a comprehensive, detailed analysis model making use of both bars and shell elements. Bars were used for the main girders, transverse beams and longitudinal stiffeners in the deck, whereas the top plate was modelled as shell elements. Relative stiffness between elements was captured by assigning them true properties. The digital automation of the 46 cross-sections used for the main girders, for instance, enabled high-quality outcomes. Accurate levels of utilization could thus be assigned to each element, enabling us identify where exactly the structure lacked capacity and thus, what measures needed to be applied and where. This is crucial for planning next steps to preserve this emblematic structure.
As well as providing an in-depth assessment of an asset’s load bearing capacity, Arup’s model can also be used for key planning aspects as the project progresses, including construction scheduling, cost control and as-built documentation.
