With coal-fired power plants, the conveyor belts which carry the coal normally end at a great height in what is known as the intermediate structure of the turbine building, which for this reason must be considerably higher than the remainder of the turbine building area.

Nuclear power plant turbine buildings do not need such a high intermediate structure, so a continuous turbine floor level and hence a level turbine building roof can be made.

In structural engineering terms, this means that the turbine building roof must span more than 40 m, as the machinery crane must be able to cover the full width of the turbine building.

Most turbine buildings for nuclear power plants therefore use pre-stressed concrete precast girders (Figure 4.6), which are usually installed using the turbine building crane which is already in place.

The roof structure in earlier turbine buildings at nuclear power plants was generally made of hollow pre-stressed concrete slabs laid directly on pre-stressed concrete girders; however, as designing for earthquakes became increasingly necessary, this solution proved to have many problems because there was no enclosed roof segment to make the structure rigid.

More recent turbine buildings therefore seek to use semi-precast component solutions, with the cast in site concrete topping being added as continuous shear slab.

There is another particular feature with designing the turbine building with boiling water reactors such as Gundremmingen. With this reactor type, the slightly radioactive primary steam is fed directly to the turbine. To protect against radiation, a thicker and therefore also heavier roof construction is required, which in turn imposes particular requirements on the design of the pre-stressed concrete ties and designing to withstand earthquakes.

The global bracing systems in the lateral and axial directions of turbine buildings vary considerably, depending on the plant context as a whole.

While only relatively soft framework systems are available laterally, the building is rigidified mainly by a shear wall in the longitudinal direction. This bracing design, which is different in the two directions of the building, means 3D modelling is often required when it comes to dynamic earthquake analysis of turbine buildings.

This is where the highly rigid spring-mounted turbine table comes in, which absorbs the high levels of static and dynamic loads from the turbine and generator and transmits it to the framework structure. The spring bodies are still sufficiently rigid in horizontal terms that in dynamic studies of how the building as a whole would behave in the event of an earthquake, the relatively soft lateral framework is ‘connected elastically’ via the turbine base.