Keywords: IFC, product model, steel construction, Produktschnittstelle Stahlbau.

The AEC-Domain is stamped by the necessary cooperation between numerous partners from diverse fields of activity, with different terminologies, software tools and work methods. Furthermore, the design of a building is a dynamic process requiring concurrent planning steps. Those characteristics exacerbate the exchange of information and finally result in losses. In the current economic situation the reduction of the costs due to those inefficiencies, i.e. the optimisation of the communication processes within the project is a crucial factor, especially for the steel construction domain because of very high commodity prices. But the latter has also some great potential, as a result of the rational production processes and the high degree of prefabrication in the factory.

Among other things, the situation can be improved by allowing the direct exchange of data between the planners, and thus avoiding multiple acquisition of information, reducing possible sources of error during and allowing better control processes. This is the purpose of product models, which are neutral standards defining the shared objects of a given domain: e.g. the Produktschnittstelle Stahlbau (PSS) [1] is a product model for the German steel construction domain. Obviously the larger the domain covered, the more efficient the interface becomes. The aim of the Industry Foundation Classes (IFC) product model [2] is to model the whole AEC industry, but does not provide any objects for steel construction detailing yet. This paper presents the main investigation steps and the results of a research project to define an appropriate extension to the base of the PSS, as well as the benefits of this extension.

The first step for the definition of the product model extension is the determination of exchange scenarios, i.e. which planners share what information. The relevant use cases for the steel construction domain are listed in this paper. Attention should be paid to the degree of detailing of the exchanged information, which is low in the vertical direction between different domains, and high in the horizontal direction within one domain. This will allow a useful implementation of the new objects in the model architecture ensuring data consistency and model integrity.

After the analysis of the exchange scenarios, the information contents, i.e. the required objects and their properties were determined. The properties are differentiated with regard to the explained distinction between horizontal and vertical data sharing. In the first case detailed manufacturing information should be transferred, in the second at least the 3-D geometry of an object. The steel construction detailing extension requires four categories of objects: basic language resources, building elements for the rough design, processing features machined on building elements and connection elements. The two first already existed in the IFC, the two last were to define. The model must provide a terminology for cutouts, holes and recesses, marks and tags on building elements, curved or bended members and treated member surfaces concerning the processing features and for welded, bolted or glued connections.

Finally the IFC model architecture was analysed to ensure a compatible extension. More information about the architecture can be found in the paper and in [2]. From there on, the requirements to the steel construction extension of the IFC were investigated and the corresponding IFC objects as well as their attributes were defined.

The developed steel construction extension allows the extensive description of all domain specific construction details. It enlarges the applications of the IFC and provides great advantages for the steel construction industry. The IFC are an international standard, and thus the ideal tool for the processing of cross national projects, which becomes accessible to this AEC branch. Due to the actual economic situation, numerous steel construction companies enlarged their activity to "turnkey" constructions, and often operate as general contractors. Thus they have to work in different areas of activity and handle data from it. They may also be responsible for the project coordination. Therefore it is obvious that the availability of a product model which extends over a lot of domains is particularly useful, e.g. it simplifies the detection of planning inconsistencies in the overall building model. All semantic resources of the model extension are now available. The final task is to implement them in the diverse software applications.

1

Deutscher Stahlbauverband, "Standard description for the product interface steel constructions", Part 1-3, http://www.stahlbauverband.de, 2002.

2

International Alliance for Interoperability, "Industry Foundation Classes IFC 2x Edition 2 Addendum 1", http://www.iai-international.org/Model/R2x2_add1/index.html, 2004.

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