‘Strength is essential, otherwise unimportant.’
Traditional structural seismic design approach is to design buildings so they behave inelastically and to provide sufficient ductility to prevent brittle failure of structural members, joints, and eventually the whole system. The inelastic behavior of buildings manifests itself by way of significant structural damage post-earthquake. This structural damage can at times require very high repair costs or can prevent functionality of the building for a considerable time. Rather than designing the building to have structural damage which is to be repaired later, recent advancements in earthquake engineering include increasing use of low-damage design philosophy. Low-damage design is by definition designing buildings so there is minor, negligible or easily repairable structural damage in a building subjected to design level earthquake. One of the most efficient low-damage seismic systems is Unbonded Post-tensioned Precast Concrete (UPPC), in which structural damage is concentrated in a specially designed joint interface. Moreover, post-tensioning strands are designed to remain elastic, which causes the building to re-center after the seismic event, thus minimizing residual deformations. However, this system has unique aspects which prevent it to be modelled and analyzed with conventional methods and computer software. In addition, performance criteria cannot be defined for these systems as it is defined for conventional systems. The gap-opening behavior, un-bonded nature of strands and low energy dissipation capacity require special analytical and modelling techniques for these systems. This article explains in detail the peculiarities of Unbonded Post-tensioned Precast Concrete systems and introduces the reader to a computer program written to obtain their moment-rotation behavior.
You can read the article here