Dimensionamiento global de losas de hormigón pretensado con tendones no adherentes

Global design of unbonded tendon prestressed concrete slabs

Unbonded tendon prestressed concrete slabs, present such particular conditions of simplicity and regularity, which permit a global design based in very few parameters (slab height and, once defined the prestressing tendon shape and distribution, the stressing force of each direction) being fundamental in the flexural behaviour of the structure. An analysis of the most determinant conditions for prestressing design has been developed, concluding that serviceability limit states linked to cranking and cover limitations are decissive. Although ultimate limit state is often determinant, in general it occurs locally, leading to require complementary passive reinforcement in areas where normally it is already needed by other reasons. This work presents the design of this kind of slabs, in a global manner, through a simple but accurate way. Design is based on minimizing cost of parameters being really global those mentioned, which at the same time are able to vary. This parameters are relationated by the design determinant conditions (in general, zero compression is adequate, but another cranking condition can be taken). So, an objective design, dealing with global parameters jointly and not separately is obtained. At the end, the proposed design process is applied to an example.