Structural Design and Connection Design for 74 Recycling Material Silos under Extreme Loads
At the core of the project were 74 new recycling material silos with structural heights of up to 35 m. The facility was complemented by pipe bridges, maintenance platforms, walkways, and escape stair towers. With approximately 800 t of installed steel, the project developed into one of the most challenging industrial projects undertaken by the company. The combination of high vertical loads, complex connection details, and increased seismic requirements necessitated precise digital planning as well as transparent and verifiable structural design checks.
Project Overview
The new silo facility was conceived as a central component of the plant expansion. It serves the storage of large quantities of recyclable materials for industrial processing. The installation comprises several silo clusters of different sizes, which are interconnected by a complex system of pipelines, maintenance walkways, and steel structures.
The geometric range of the silos was exceptional. The diameters range from 2.5 m to 4.5 m, and the storage volumes vary between 125 m³ and 400 m³. In the filled condition, each individual silo reaches an operational weight of up to 350 t. In addition, pipe bridges, platforms, and escape stair systems had to be integrated into the global structural system to ensure safe operation as well as maintenance access and escape routes at heights of up to 35 m.
Engineering Challenges
A key challenge already arose during the conceptual design of the silo substructures. The containers, with heights of up to 35 m, are supported on circular ring beams, through which the high vertical loads must be uniformly transmitted into the steel substructure. Even minor geometric deviations may result in undesirable eccentricities and additional stresses in the silo shell.
To reduce these risks, essential structural components were preassembled in the fabrication workshops of Stahlbau Süssen. This fit-up and quality control ensured that ring beams, platform elements, and connection details could be erected on site with high accuracy.
Further complexity resulted from the interaction of various structural components. Main columns, ring beams, bracing systems, pipe bridges, and platforms had to be coordinated within a three-dimensional global structural system. At the same time, significant actions from self-weight, imposed loads, operational conditions, and dynamic effects had to be considered.
Seismic Design under High Actions
A particular challenge resulted from the project location in Rheinfelden within the Upper Rhine Graben. The site is located in a region with increased seismic activity. In combination with the considerable structural heights and large moving masses, this results in significant horizontal actions and correspondingly high internal forces.
The entire structure was modelled in Dlubal RSTAB. The detailed global model enabled the precise determination of support reactions and internal forces for subsequent design. However, the highly loaded joints as well as the massive base connections required advanced analysis beyond conventional simplified verification methods (Figures 5a, 5b).
Conventional verification procedures would have resulted in considerable manual effort due to the large number of connections and the complexity of load combinations. At the same time, there was a risk that overly simplified assumptions could lead to unnecessarily heavy structures.
Solution Using IDEA StatiCa
For the verification of the governing connections, the team used IDEA StatiCa Connection in combination with IDEA StatiCa Checkbot. Due to the direct interface to RSTAB, the calculated internal forces could be transferred to the connection design without manual intermediate steps.
This enabled a continuous digital workflow between the global structural model and the detailed design. The engineers were thus able to analyse highly stressed joints and assess stress distributions as well as plastic strains in a transparent and reliable manner.
Particularly for base plates and main column connections, the CBFEM technology provided valuable insight into the load-bearing behaviour of the connection zones. Local stress peaks were identified and reduced by targeted measures, such as the addition of stiffeners. At the same time, it was verified that all connections satisfy the required safety levels even under exceptional loading conditions.
Results
By combining global modelling in RSTAB with connection design in IDEA StatiCa, Stahlbau Süssen was able to carry out the preliminary and detailed structural design for the 74 silos and the associated ancillary structures efficiently and transparently.
The digital consistency between global structural analysis and local connection design significantly reduced manual effort and minimized potential transfer errors. At the same time, the detailed analysis of the joints enabled targeted optimization of the structure without compromising the required safety margins.
The result is a high-performance steel structure with a total weight of approximately 800 t, which meets both the exceptional operational actions and the increased seismic requirements at the site. The close integration of structural design, detailing, and fabrication enabled the safe realization of one of the largest silo projects in the company’s portfolio.
About the Structural Engineer
Bilal Al Dukhan is a civil engineer and structural engineer at Stahlbau Süssen GmbH. Within the project, he was responsible for essential parts of the preliminary and detailed structural design, as well as for the design of steel connections. His focus lies on economical and practical solutions for complex structures in industrial and steel construction.
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