A Simplified Procedure for the Seismic Design of Hybrid Connections in Precast Concrete Structures

The correct use of non-adherent prestressing techniques in beam-column connections can significantly increase the seismic performance of precast concrete frames, making them a competitive alternative to the traditional cast-in-place concrete structures. In this sense, a fundamental factor of the nodes’ design is represented by the correct calibration of the ratio between the amount of mild steel and that of post-tensioned reinforcements, in order to provide the prescribed flexional and rotational capacity to the beam-column interface, and to guarantee at the same time the required dissipative and re-centering capacity. In this paper, a simple algorithm for the optimal and quick pre-dimensioning of the above mentioned parameters is proposed. It is based on the knowledge of the materials’ mechanical parameters and of the “target” stresses and deformations corresponding to the required performance level, which can be computed either through a Force Based Design approach or by a Displacement Based Design approach. In the case of centered post-tension and in the presence of symmetrical mild steel, the procedure can also be effectively represented in a graphical form, making it is easily possible to determine the post-tensioning stress that should be applied to the cables in order to guarantee that they remain in the elastic field after the seismic event, and to obtain the recentering of the system