Campus Arlesheim
A Competence Centre for Industry 4.0
On the former factory site of Stamm Bau AG, the Schorenareal in Arlesheim, uptownBasel AG is developing and realising a modern campus in the immediate vicinity of the economic centre of Basel. The aim is to establish a leading location for Industry 4.0 in Switzerland on the new campus. The shell of the first of several buildings is currently nearing completion. The future-oriented building will be available for tenants with automated work and production processes and will be as flexible and modular as possible. The ground floor is largely column-free - the three storeys above are supported with the help of lattice girders. The parts of the two upper storeys that protrude on all sides are supported by external trusses. Without the use of steel as a key design factor for the supporting structure, none of this would be possible in its present form.
Idea of the campus and the first building
UptownBasel AG is currently developing and realising a new, future-oriented campus specifically for Industry 4.0 on the former factory site of Stamm Bau AG, the Schorenareal in Arlesheim (Fig. 1). The first building is nearing completion and is set to become a centre of excellence for Industry 4.0 (Fig. 2). With this in mind, the planning of the new building is focussed on ensuring that it can be used extremely flexibly. The production areas are to be largely column-free so that they can be customised for the respective tenants with automated work and production processes.
The use of sustainable building materials is also an important aspect with high priority - sustainability is considered through the selective use of recycled concrete in reinforced concrete components and the targeted use of steel as a building material. In line with Industry 4.0, the planning process will also be digitalised - this will be implemented specifically in the structural calculations and the creation of all necessary plans and planning documents.
Campus for Industry 4.0 (Fig. 1)
Copetence Centre for Industry 4.0 (Fig. 2)
Structural concept and construction of the building
The building has a length of around 100m, a width of around 60m and a height of around 24m. It consists of a basement with a parking lot, an overhigh unsupported ground floor as well as three upper floors (Fig. 3). The two uppermost storeys are overhanging on all four sides of the building. The ground floor is intended as an industrial production area, above that is a technical storey. In the two upper storeys, office space will be installed.
In order to guarantee column clearance in the over-height ground floor, the entire storey above is designed as an interception level with storey-high lattice girders. The truss girders run in the longitudinal direction of the building (marked in orange in Fig. 3) and transfer the loads from the floor slab (marked in yellow in Fig. 3), which is constructed using prestressed Pi slabs with in-situ concrete additions, and the floors above directly or via additional truss structures running in the transverse direction of the building to the reinforced concrete cores and a series of precast columns on the ground floor. This way, the support-free room on the ground floor can be enabled. In order to fulfil the requirements for structural fire protection, the steel structure of the interception level is either protected using drywall construction or coated with fire protection spray plaster. The building services are arranged in the storey that acts as an interception level. Building service pipes can run between the supports and diagonals of the trusses. The support structure is designed to absorb the loads from a further mezzanine floor below, which is suspended from the steel structure - this can be realised as part of a later building extension and is already being built in parts at present.
In the two upper office storeys, a column grid of up to 7.50 m with reinforced concrete ceilings is used, some of which are designed as hollow-core slabs to reduce weight. There are no further supporting structures on the office floors. The overhanging areas of the floor slabs are supported on truss structures running along the façade level (marked in green in Fig. 3). The base points of the inclined columns and their respective load transfer are located either directly on the reinforced concrete cores of the short sides of the building or on the longitudinal sides of the building on the trusses of the intercepting storey in the immediate vicinity of their supports. Steel structures are generally only used to transfer the vertical building loads. The steel trusses are described in detail again in sections four and five and their special features are shown. A total of approx. 1200 tons of structural steel is used for all steel structures.
The building is braced for seismic loads via the ceilings as horizontal slabs and the six reinforced concrete cores running across all floors. The foundation is a shallow foundation with an elastically bedded reinforced concrete floor slab with individual piles in the area of concentrated support loads.
Cross section Competence Centre 4.0 (Fig. 3)
Digital planning in the sense of Industry 4.0
During planning, a high level of consistency should be ensured with the digital tools used. With this in mind, an overall model is used in the Revit software (Fig. 4).
The model is the basis for project planning and tendering as well as for the entire formwork and reinforcement planning and the steel construction overview plans for the project. All plans are generated from the building model. Thanks to specific component information in the sense of BIM planning, quantity and cost information as well as component lists are also derived from the model. In addition, the Revit model is the basis for the computerised static calculation of the steel and reinforced concrete structure. The model can be used to generate static models in the SOFiSTiK and RStab software packages. The design of structural elements such as reinforced concrete floors, walls and internal and external steel trusses is primarily carried out using sub-models, so-called subsystems. To calculate the behaviour of the building under seismic loading and to check the plausibility of the load flow in the numerous interception areas and the interaction between the reinforced concrete structure and the façade trusses, an overall model is generated from the Revit model in SOFiSTiK and calculated there (Fig. 5).
Overall model using the software Revit (Fig. 4)
Overall model using the software SOFiSTiK (Fig. 5)
Overhangning storeys through external façade trusses
To transfer the vertical loads from the overhanging ceiling areas on the four sides of the building, the truss constructions running over the height of the two upper storeys at façade level are used (highlighted in the Revit model in Fig. 6, shown as a static partial model in RStab in Fig. 7). The ceiling loads are transferred via the façade trusses to the inclined columns arranged on the longitudinal and transverse sides. These rest directly on the walls of the reinforced concrete cores on the transverse sides and on the inner trusses of the technical floor on the longitudinal sides. The further transfer of loads from the façade trusses then takes place there. The ceiling loads are transferred to the external trusses in the three affected storeys via steel brackets inserted into the reinforced concrete ceilings. In the centre of the three storeys, the ceiling loads are transferred to the truss diagonals via the brackets, which means that the diagonals are not only stressed by the normal forces resulting from the truss effect, but also by bending. Strictly speaking, the façade trusses are therefore no longer a pure truss system, but the truss effect clearly dominates in comparison to the bending load-bearing behaviour.
One of the special features of the façade truss construction is that it is located outside the insulated building envelope and is therefore exposed to climatic temperature fluctuations. The steel structure is designed to be able to absorb temperature fluctuations of up to +/- 30°C in theory. This results in normal forces of up to approx. 4 MN with alternating signs in the upper and lower chords. The support brackets at the slab edges are therefore not only designed to transfer the vertical loads from the reinforced concrete slabs, but also to transfer the horizontal constraining forces from the temperature differences into the reinforced concrete slabs - in the brackets as horizontal shear forces. In addition to the shear forces, high normal forces from temperature differences occur in the brackets of the building corners arranged at 45°. The nominal forces are restrained in the floor slabs by the reinforcement connected to the brackets.
The upper and lower chords of the façade trusses generally consist of hot-rolled square tube profiles 400 x 400 x 20. Greater wall thicknesses are required in the node areas (up to 30 mm) in order to be able to absorb the node stress. Standard hollow sections are no longer available with these sheet thicknesses as standard. For this reason, as well as in order to be able to produce the complex node geometry, hollow profiles welded from individual sheets are used here. The joints to the adjoining rolled hollow sections are partially welded or generally bolted. The screws are partly external and partly concealed in the hollow box. Assembly takes place at the installation site; after bolting in the box girder, it is tightly sealed with welded covers. The diagonal braces are designed as H-profiles. Their connections to the top and bottom chords are made using stubs welded to the node area, the actual diagonal is then connected with a bolted end plate joint.
Due to the special geometry, a finite element model with shell elements in the SOFiSTiK software is used to assess the load-bearing behaviour of the upper node between the inclined columns, upper chord and subsequent diagonals of the truss (Fig. 8). At these nodes, the calculation using a pure beam model supplemented by manual calculations is not considered to be sufficiently meaningful, so the finite element model is used.
The calculation of the finite element model is geometrically and materially non-linear, considering the plastic redistribution possibilities in the material. The evaluation is therefore strain-based, and the structure is designed in such a way that the strains caused by the redistribution are well below the limit values. By transferring the vertical loads from the upper chord of the truss via the gusset into the inclined column, horizontal deflection forces are generated at the column head. These are suspended back into the reinforced concrete ceiling via the ceiling bracket and the reinforcement connected to its end.
Figure 9 gives an impression of the design and assembly of the steel structure of the façade trusses. The individual parts of the steel structure are assembled and bolted together directly at the installation site.
Façade level in Revit-model (Fig. 6)
Structural partial model using RStab (Fig. 7)
Finite-Element-Model with shell elements in the SOFiSTiK software (Fig. 8)
Design and assembly of the steel structure of the façade trusses (Fig 9)
Column clearance due to wide-span truss girders
The storey above the over-height ground floor serves as an interception level to ensure that the ground floor is free of supports. On this level, storey-high trusses are arranged in the longitudinal direction of the building and bracing in the transverse direction (highlighted in the Revit model in Fig. 10, shown in the as-built state in Fig. 11).
The upper and lower chords of the truss structures are each embedded in the reinforced concrete ceiling above and below the interception floor in beams. The tractive forces in the bottom chords are only absorbed by the steel profiles. The upper chords are designed as horizontal composite columns, and the surrounding in-situ concrete downstand beam is also used to absorb the compressive forces. To transfer compressive forces from the compression areas of the steel chords to the reinforced concrete beams, shear stud dowels are arranged at the force transfer points (nodes of the truss top chords with normal force jumps). This achieves local activation of the bond between the steel girder and the reinforced concrete cross-section in order to optimise the steel cross-sections and transfer some of the compressive forces via the reinforced concrete structure. The structural analysis of the internal trusses is carried out in the SOFiSTiK software using the bond between the steel components and the reinforced concrete floor (Fig. 12). In the structural model, all prestressed and unprestressed states with and without bonding with the reinforced concrete structure during the construction period are also modelled and taken into consideration.
The inner trusses bear the loads from the columns of the office storeys above. These stand on the truss nodes of the upper chords. The inclined supports of the façade trusses are located close to the supports of the inner trusses, which means that the loads from these are not absorbed by the trusses but are transferred directly into the reinforced concrete structure or into the transversely running trusses. To be able to realise access routes as passages through the inner trusses on the technical floor, which acts as an interception level, the middle bay of the truss girders is designed as a Vierendeel frame without diagonals. This means that in addition to the normal forces typical of a truss, the truss also receives bending loads at this point, which must be absorbed by the frames. The inner trusses are made of H-sections and are welded together in close proximity and then lifted to their installation location in one piece and installed there.
The inner trusses are supported either directly on reinforced concrete cores on steel inserts or indirectly by means of transverse trusses. The trusses are also supported on steel inserts. The steel inserts are each storey high and are installed as a fully reinforced component. To transfer the high bearing forces of up to approx. 9 MN centrally into the reinforced concrete structure, centring sides are welded onto the steel inserts.
The bracing structures form the connection between reinforced concrete cores or rest on prefabricated columns on the ground floor and transfer the loads from the trusses to them. In some cases, the bracing is integrated into the reinforced concrete walls, whereby the inclined columns in the walls are also designed as composite columns.
Frameworks in the longitudinal direction of the building and blasting structures in the transverse direction (Fig. 10)
Construction status (Fig. 11)
Structural calculations of the trusses using the software SOFiSTiK (Fig. 12)
Current status of design and outlook
Currently the shell construction of the building is near termination. All reinforced concrete ceilings up to the roof have been put in place, the steel construction assembly of the inner and outer trusses is complete (Fig. 13). The supporting structure is completely activated since the temporary injections have all been removed. Currently the assembly of the façade is being worked on, simultaneously an intermediate level suspended from the inner trusses is already being installed in steel construction with a composite sheet metal ceiling.
The handover of the fully functional building is set for the end of 2021. The second building should be finished by the end of 2022, the first work on this building are currently starting.
Steel construction assembly of the inner and outer trusses (Fig. 13)