The geometries can be directly generated from the RIB FEM system
Dr. Mark Beckmann
The engineers of ahw GmbH feel comfortable when they have to solve challenging tasks. They are pioneers when it comes to technology and their finite element simulation makes a decisive contribution to more economic efficiency in construction projects. When working with particularly complex geometries, such as when planning the self-supporting corkscrew spiral staircase of the new photovoltaic research centre in the capital, they appreciate the structural analysis software of the Stuttgart construction software manufacturer RIB.
From solid masonry to steel and wood, high-strength concrete and shell structures to cable, membrane and composite construction: ahw Ingenieure GmbH have an exceptionally diverse portfolio in the field of structural planning. This structural engineering planning office, active worldwide and with a presence in Münster, Hamburg, Halle and Berlin, promises its client base more than just “business as usual.” 70 employees, of which 40 are structural engineers, bring more than just extensive knowledge encompassing all fields of structural planning. ahw’s specialist fields include, alongside finite element simulation, the use of technology from the aerospace aeronautics industry. This has been developed by the ahw engineers for the requirements of structural planning and make an essential contribution to cost-optimized construction.
ahw is the only engineering office in Germany to use the advantages of these innovative technologies to computer-simulate digital prototypes of large-scale projects. Here, the structure is fully simulated, making it possible to alter all geometric and physical parameters for any set of applied forces and temperatures. The advantage: The virtual prototype shows how to achieve economical solutions before they are built. Compared to traditional FE calculations, the engineers have been able to save 20 per cent on materials in previously realized projects by using these methods. Alongside structural engineering tools, software developed originally by the NASA for the automotive industry is used, for example for crash evaluation and optimization in vehicles. In addition to these innovative technologies in the field of finite elements, the engineering office also brings a great store of experience in large-scale projects and extensive competences to bear.
Among the most recent reference projects of the office is the new build of the Photovoltaic Research Center in Adlershof, Berlin, designed and planned by the HENN architectural office, Munich/Berlin. On a gross area of 13,000 square meters, a multi-functional building for companies in the photovoltaic sector and those engaged with renewable energies was built commissioned by the client WISTA Management, Berlin. The building was designed as a pentagon and consists of a first floor and three upper stories. In addition, there is a cellar area to provide technical spaces.
The new research center consists of a hall of around 2,000 square meters for pilot projects and other applications, a workshop with an area of around 500 square meters, a canteen with 75 seating spaces and a foyer on the first floor with a free-standing spiral staircase spanning three stories and connecting the upper floors with each other. A particularly energy-efficient building in design and usage, the research center has received the SILVER certificate from the German Society for Sustainable Construction (DGNB). A ground-level gas store supplies the tenants via subterranean pipelines with nitrogen and other gases that are required in the photovoltaic research laboratories. Employees can also charge their electric vehicles or e-bikes at a special charging station.
The site on Johann-Hittorf-Straße was redeveloped in the course of creating commercial spaces. The foundations of the areas not built over basements were designed as shallow foundations with strip and point foundations. For the areas with basements, an elastically bedded base plate was used. Ceilings/floors were essentially designed as flat slabs. They are borne by columns and edge beams. In the hall area, the ceilings are linearly supported on reinforced concrete beams. TT plates span the individual modules in the interior courtyards. Exterior walls and interior load-bearing walls were built in reinforced concrete. Non-bearing interior walls on the lower story were partly built in masonry. All bearing columns were in reinforced concrete. The basement was built in impermeable concrete. The stairways in the building were built as prefabricated elements with connecting reinforcements for the landings (which were cast on site), so that the reinforced steel stair treads and landings in the emergency exit stairwells are monolithically bound together. Stairwell 5 is a steel structure. Overall connection between the stories is made via the solid, free-standing spiral staircase in the foyer. The bracing of the entire building was realized by the engineers through the reinforced steel wall plates and ceiling plates.
The self-supporting spiral staircase is the most demanding construction in the entire building . The curved shell structure of reinforced steel, consisting of stairs, landings and parapets, bears loads predominantly through the self-supporting interior and exterior parapets and the star treads in the foundation. A proportion of the loads are transferred via the connection with the upper floors to the load-dissipating components in building axes 8 and 9.
The landings are monolithically bound to the story ceilings. On the first and second floors, the ceiling was modeled up to the neighboring wall. The fixtures of the ceiling to the neighboring ceiling panels and the wall are elastic. On the third floor, a different load-bearing system is present, where the landing is borne on an elastic bearing.
The experts from the ahw office undertook a detailed investigation of the statics of the spiral staircase with the FEM software TRIMAS by RIB. Dr. Mark Beckmann explains why the RIB software is particularly good for complex spatial structures such as these: “The geometries can be directly generated from the RIB FEM system. It is not necessary to transfer the individual points from the architectural CAD model.” In this way, the structural planners at ahw not only save processing time but are also able to work in a much more exact way.
Beckmann again: “When we work with points from CAD-specific dwg or dxf files, unexpected kinks in the surfaces can arise. With our working method in TRIMAS, we instead receive a flat geometry, just as the structure is to be executed later in practice. In this sort of shell calculation, such miniature details are exactly what it all comes down to,” the expert says. Where the double-curved stairs are concerned, suitable finite element methods are of particular relevance. Due to the quadratic approach functions, the mapping of the geometry and the mechanical support behavior via the use of the shell normals can also be detected correctly for this helical structure.
For the Photovoltaic Research Center, the engineers from ahw carried out calculations for a free-standing spiral staircase for the first time with TRIMAS. The engineers from ahw enjoy the challenges of new structural planning tasks. Here, they worked with so-called “isoparametrically networkable surfaces” for the generation of a doubly-curved FE network which was used for the inner and outer parapet of the stairwell and stairs. Here, TRIMAS offers the ability to make very individual graphical inputs. The isoparametric networks created with the aid of the RIB software are not – as in other programs – arbitrarily inserted in the stair area.
According to the engineering office, TRIMAS and other RIB programs are in all very well suited for statics calculation and assessment, especially when the geometries get more complex, as they offer the structural planner many degrees of freedom, especially in demanding models. For structural engineering tasks outside the sphere of the everyday this is always a great advantage, as Mark Beckmann and his colleagues confirm. The final crowning achievement of the engineering works was the transferal of the design of the spiral staircase into the reinforcement plan. Here, the determined reinforcements had to be inserted in such a way that the demanding geometry with all connections across the individual concrete sections could be flawlessly and efficiently laid out on site.