Sometimes, the architectural design of a building relies on a concrete treatment without which its construction would not be possible. This is the case with post-tensioned concrete. Post-tensioned concrete is a type of concrete to which internal compressive stresses are applied in order to compensate for and reduce the external tensile stresses to which its function subjects it. These compressive stresses are applied to the concrete elements by means of a series of steel cables that run, encapsulated in plastic sheaths, through the interior of the concrete. A series of jacks at the ends pull on the cables, compressing them with forces opposite to the tensile forces they are subjected to in the structure.
Other architectural designs call for pre-stressed concrete to be used in the construction of the building. This is similar to the system described above, with the only difference being the moment at which the tensioning of the cables is applied. So, in post-tensioning, the cables are tensioned in situ, during construction and once the part is concreted. In pre-stressed concrete, on the other hand, the compressive forces are applied before pouring, by stressing the cables and in prefabrication.
The main advantages of post-tensioned concrete are as follows:
- Reduction of the cross-section of the elements, resulting in material and cost savings, and a slimmer and lighter design and architecture.
- It requires little maintenance after construction.
- Most importantly, it increases the service life of the elements. By reducing cracking, of which tensile forces are precisely the main cause, concrete is less sensitive to external agents that generate pathologies in it.
Post-tensioned concrete has generally been used in the construction of bridges, viaducts and airports. In recent years however, it has begun to be used in architecture for floor slabs and building foundations. This results in extremely open spaces with a reduced thickness of the concrete elements. A clear example of the application of this construction method is the Veles e Vents building in the port of Valencia, Spain. Here, the floor slabs are made of post-tensioned reinforced concrete. As a result, the building is supported by four large reinforced concrete cores, with spans between them varying between 23 and 28 metres, and with cantilevers of up to 12.80 metres.
By Alberto López, Senior Structural Engineer at Amusement Logic’s Architecture Dept.
