||Tekla Oy is developing a software package called Xbuild for the design and detailing of steel and concrete structures. The development focuses on two main areas: steel structure design and design of reinforced concrete structures. Accordingly, Xbuild consists of two main parts: Xsteel and Xconcrete software modules. The basic idea behind the Xbuild is to build a logical product model of the steel concrete structure. This product model is stored in a relational database and it is created by using sophisticated interactive 3D-modelling tools. All documentation needed for the manufacture and construction of the structure - drawings, material lists, NC-preprocessor files - can then be produced from the product model. Xsteel includes modelling tools for beams, columns, connections, plates, weldings, bolts and other components of a steel structure. Most of the standard components used in Finland and other European countries are stored in component libraries such as profile, connection and bolt libraries. The modelling is object-oriented, which makes the model "intelligent". Every component in the structure is an object in the product model database and objects can be connected to each other by certain rules. In practise this means that for instance when a beam is being moved, the adjoining joints will follow. Every object is stored in the database only once, which ensures the coherency of the database in all situations. The 3D-model, drawings and lists are just "views" to the database - all design modifications can only be made in the model. This way the user can be sure that all documentation of the model is always up to date. Xconcrete is based on the same principles as Xsteel. The main difference is that Xconcrete can also handle the reinforcement bars in an intelligent way by utilizing object-oriented techniques. The database structure of Xsteel and Xconcrete is relational. The contents of the database can be written out in any format specified by the user. This enables data transfer between Xbuild and any other product model based software. It is also possible to link other applications, such as strength analysis and dimensioning, production planning and cost calculation, to Xsteel by using an open linking inter- face. In addition to this, the Xbuild software modules include tools for creating user specified macros - a feature that enables users to develop own Xbuild "applications". Today Xsteel is used by several engineering and steelwork companies in Finland as well as abroad. Xconcrete is still partially under development and will be completed in the near future. As the construction process, codes of praxis etc. differ a lot in different countries, the requirements set on the software vary quite much from one country to another. Therefore the software has to be easy to adapt into different design environments. The results gained by the users show that the product model based approach is radically improving the productivity and quality of the design work. On the other hand it is clear that using a sophisticated product model based design software sets new requirements for the designers and manufacturers of structures.