Analysis on columns of multi-story buildings in precast concrete during the transitory stage

ABSTRACT

Differently cast-in-place structures, precast concrete systems basically have the following particularities: design of connections and consideration of other calculation situations other than the final design. These situations are the phases of the transitory stage, involving: demolding, storage, transport and assembly. At this stage, the part may present static schemes and different requests, which may cause a more critical condition in E.L.U or E.L.S. As an example, we can mention the case of the precast column that during this stage presents a beam behavior due to its horizontal position. Still, the objective of this work is to carry out a study of the position of the lifting loops in a precast concrete column that presents critical transitory phases, in order to seek an admissible position of these support that results in the best distribution of requests and cracking control. For this, a parametric analysis was carried out during the demolding and assembly phase with the element having 2 handles, whose parameters obtained with the variation of the position of the handles were: bending moments, tension in the reinforcement and stiffness reduction coefficient for the most requested sections. Subsequently, the same parameters were obtained, however using 3 handles at the time of the serve and 3 points for lifting, totaling 3 typical positions of static scheme for these phases. The results showed that by using 3 handles it was possible to control cracking, reducing the necessary reinforcement and tension in the same. The parametric analysis showed that the stiffness of the element would be greater than 0.50.EI only with a stress level below 0.30, showing that not necessarily limiting the tension in the reinforcement to 0.50.f_yk is assurance of ELS-F admissible, also showing that the loss of stiffness in a transitory stage must be considered, since it is not enough to meet the normative conditions only in the final stage of the project.

Keywords
Precast structure; Precast columns; Cracking; Transitory stage; Parametric analysis