STUTTGART 21: DIGITAL WORKFLOW ON THE PROJECT OF THE CENTURY

It is the largest German expansion project in rail transport since the 19th century.

Allplan in practice

As part of the Stuttgart-Ulm rail project, four new stations, 120 kilometres of new railways, over 10,000 new jobs and two completely new quarters are being built. But it‘s not just the size that makes this project of the century so impressive. On top of this, engineering history is currently being written here - both in terms of design and technology. Special attention will be paid to the station concourse of the new underground station in Stuttgart, designed by ingenhoven architects. An architecturally highly sophisticated shell roof, supported by 28 geometrically highly complex goblet supports, qualifies this as a masterpiece of modern architecture that the world has never seen before.

Without the use of powerful BIM software and production processes specially developed for the project, the implementation of the building would be impossible. The engineering firm Werner Sobek AG, which was responsible for the structural, shell and reinforcement design of the station concourse, therefore relied largely on 3D for the design. On the basis of this 3D planning, the company Ed. Züblin AG is now fully exploiting the advantages of BIM during implementation thanks to Allplan Bimplus. A prime example of a digital workflow in construction.

PROJECT INFORMATION AT A GLANCE

>Focus: Engineering
>Software reinforcement design: Allplan Engineering, Allplan Bimplus
>Client: DB Projektbau GmbH, Stuttgart/Germany
>Design: ingenhoven architects
>Structural, shell and reinforcement design: façade design: Werner Sobek AG
>Execution: Ed. Züblin AG
>Planning period: 2010 – 2020; remaining work until spring 2021
>Execution time: 2011 – 2025


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Demanding form

The station hall for the new underground station in Stuttgart is to be approximately 420 metres long and 80 metres wide. The associated shell roof - a highly complex structure of anticlastic curved surfaces - can be mathematically described as free-form, since there are no mathematical regularities that describe it. Despite all apparent freedom, however, this shape is by no means arbitrary, but rather follows the course of forces in a highly efficient manner and implements the requirements of a wide-span and light-flooded station concourse in a material-optimized way. It is supported by 28 goblet supports, which can be divided into 23 standard supports with edge-reinforcing cover (scoop) on the upper side, four flat goblets without edge-reinforcement and a larger special goblet, which opens as an access area to the city centre.

Due to its enormous geometric complexity, the shell roof had to be planned completely in 3D. In collaboration with Werner Sobek AG, ingenhoven architects generated a 3D model in Rhinoceros. In addition to the pure surface geometry, the model also contains further information such as formlining joints and the coordinates of installation parts. It served as a planning basis for the object planning of ingenhoven architects, the shell and reinforcement planning of Werner Sobek AG as well as for the development of a formwork construction by ZÜBLIN. the reinforcement design proved to be very complex due to three boundary conditions: Firstly, the geometry with constantly varying component thicknesses, synclastic and anticlastic curved areas as well as a combination of circular and orthogonal reinforcement systems led to complex transition and overlapping areas with multiple crankings and bends. Secondly, high demands on the visible surface required small deviations in the concrete cover and extremely precise bending forms. Thirdly, the accuracy in the manufacture of the complex bending shapes of the reinforcing bars was limited.

12,000 reinforcement drawings for one roof

Based on these boundary conditions, Werner Sobek‘s engineers created socalled tracks (reinforcement axes) with Rhinoceros in combination with Grasshopper and C# for the reinforcement of the free-form geometry using the 3D model next to the surface. Since these tracks consisted of splines and could therefore not have been produced economically, the geometry had to be simplified in a first step. This could be solved by means of specially developed scripts, which were used for parameterized simplification and grouping of bar shapes. In this way, bending forms coordinated with Ed. Züblin AG were achieved as curved trains with up to three arcs and polygons.

The engineers in Allplan Engineering produced those bars that did not have a free-form geometry. The previously mentioned final traces were then also transferred to Allplan and, together with the reinforcement already generated there, processed into an overall reinforcement model including all bar properties, reinforcement-relevant inserts as well as concreting and vibrating coils. On the basis of this 3D reinforcement model, a collision check was first carried out and then the reinforcement drawings were generated. A few figures reveal the enormous complexity: 350 DIN-A0 drawings include the reinforcement design of a typical inner cup with a reinforcement mass of about 300 tons. Approximately 1,500 different positions occur per calyx. A typical rim cup, with around 350 tons of reinforcement steel, has 400 drawings. The total shell roof is shown on 12,000 reinforcement drawings.

Optimized design thanks to Allplan Bimplus

The reinforcing bars are bent in a bending shop specially set up for the project, mainly by means of an interface between the bending machine and the reinforcement model, and checked by means of true-to-scale laser projection. 11,000 different, partly three-dimensionally curved bar shapes, including many unique specimens, have to be placed per calyx on the construction site. In order to ensure exact positioning, each component of the shell roof is provided with a coordinate list with Gauss-Krüger coordinates in addition to the reinforcement drawings. With the help of a surveyor, the guide bars can be precisely measured and further bars can be placed between them. For the correct assignment of the bars, the beginning and end of the bars are defined in the reinforcement drawings, which in turn are taken over by the bending company by means of a colored marking in addition to the position number on the bar.

However, the 3D reinforcement design also improves the execution by providing further assistance: With the help of Allplan Bimplus, the 3D model is used directly on site to provide support and the installation of the irons is coordinated. ZÜBLIN uses both a large screen in the container and a mobile solution for direct access at the installation site. This makes the highly demanding production of reinforcement much clearer and much easier, which illustrates the enormous benefits of a digital workflow in this masterpiece of civil engineering - from design to execution.

„Allplan Bimplus is an essential component of the newly developed digital work processes, without which it would not be possible to produce the architecturally very sophisticated roof construction.“

Bernd Mehlig, overall project manager Ingenieurbau Stuttgart 21 at the Ed. Züblin AG

Werner Sobek AG

The architect, consulting engineer and test engineer for structural engineering of all disciplines, Prof. Dr. Dr. E.h. D. h.c., founded the Werner Sobek Group in 1992. This group stands worldwide for engineering, Design and sustainability. It has more than 350 employees and operates worldwide. Werner Sobek works on all types of buildings and materials. Special emphasis is placed on building construction and façade planning. The work is characterized by high-class design based on outstanding engineering and integral concepts for minimizing energy and material consumption.

Züblin AG

Founded in 1898 by the Swiss engineer Eduard Züblin, Ed. Züblin AG is today the number one in the German building and civil engineering industry thanks to its innovative strength, which is reflected in intelligent designs, new building materials and advanced manufacturing methods. Last but not least, the member of the globally active STRABAG SE owes its success to the wealth of ideas and commitment of its 14,000 employees who, as a large team, are able to realize even complex construction projects on time and at the best price thanks to perfect processes.

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