Considerações sobre o cálculo e dimensionamento de vigas protendidas pós tracionadas

Abstract

This work deals with a study of the concepts of prestressed concrete beams in post-tension. An application example is used to discuss the required steps for calculating and detailing for this purpose. The prestressed girder of interest is one of the structural elements of a multiple-girder bridge. The geometric data of this bridge (deck slab, spars and transverses) and the layout of the prestressing strands in the girders were extracted from the works by Stucchi & Skaf (2006) and Dutra (2019). Due to the environmental characteristics of João Pessoa, the concrete specifications were conveniently changed. The prestressed girder calculation sequence begins with the definition of the initial project data (environmental aggressiveness class, relative humidity, specification of concrete strength, slump, aggregates, cement, steel for reinforcement (active and passive) and geometric configurations of the structural elements involved) Then, the effects of the dead loads on the slab are conveniently transferred to the girders, which, after adding their own weight, determine the dead stress resultants. Then, the effects of the live load, associated with the standard train acting on the slab, are conveniently transferred to the girders using approximate methods, such as Leonhardt’s process and Engesser-Courbon’s process, which after being weighted by impact coefficients, live stress resultants can be determined. After making combinations in the service limit state of dead and live stress resultants (required by the prestressing level established by the environmental aggressiveness class, post-tension system, and estimated prestressing loss) the prestressing force and its corresponding area of strands are determined at critical section. Next, the real immediate and progressive losses in the process were studied. With the construction of the limit spindle, the eccentricities of the resulting strand in the cross sections of the girder under study can be verified. Then, it proceeds to verify the normal (bending) and tangential (shear and torsion) stresses in the ultimate limit state, determining the longitudinal, transverse and complementary passive reinforcement. Finally, the prestressed girder detailing is done.