As already noted concrete has an optimum resistance to compression but a poor resistance to traction which, in reinforced concrete, is absorbed by a metal framework. Under the effect of traction the metal bars stretch and, seeing that steel and concrete are perfectly adherent, if one of the two stretches then so does the other. In the presence of strong stresses, traditionally when concrete is stretched it risks being cracked. Cracks may not compromise the stability of the structure, but they do cause deformation and reduce the protection of the metal framework, which is then subjected to oxidation, with the consequent reduction of resistant sections.

Prestressing allows the manufacture of poles capable of supporting greater stress loads than any structural element forged of simple reinforced concrete. This method pre-stresses the poles so that they are able to balance the traction determined by its own weight and the loads; metal framework is stretched by applying a traction force on the edges, the traction is shifted to the mix as compression, applying it so it complies with the pretensioning technique. When a load is applied, the bending traction in the tight part progressively removes the pre-established compression. This is why structures can be sized in a way so that the mix is always compressed at each point. The metal frameworks are stressed to the maximum of their capacity, correspondingly with the limit for mix cracking.