اثر تغییر شکل های تابع زمان بتن بر نیروی پیش تنیدگی در مخازن استوانه ای

Abstract
Prestressing techniques are generally used for the construction of large
containment shells to overcome tension and to ensure tightness. Thus, the
evaluation of the prestressing force variations considering the geometry and
mechanical characteristics of tendons becomes an important matter. This paper
considers the effects of time dependent deformations of materials on the
circumferential prestress force in prestressed concrete cylindrical containments.
Numerical studies are performed using creep and relaxation models presented in
different codes of practice after checking the numerical model by experimental
data reported elsewhere about a prestressed concrete beam. The effects of vertical
prestressing and wall thickness are also studied. Obtained results show an amount
of 15% to 22% of prestress loss in tendons, specially in those located around wall’s
mid-height , on which relaxation of steel has a dominant effect. Furthermore, the
minor effect of vertical prestresssing might be mentioned. Besides, the creep model
of Iranian concrete code is studied and some suggestions are made for the
modification of the coefficient used for the prestress losses due to relaxation
effects.