Comprobación teórico-experimental de las fuerzas remanentes en tendones de pretensado exterior

Theoretical and experimental checking of remaining forces in external prestressing tendons

Externally prestressed beams represent a very suitable structural solution, with many advantages such as economy of materials or execution easiness, being also more practical for operations of reinforcement and/or repair. However, this constructive technique requires special cares to ensure good agreement between the ?as projected? and the ?as built?. This system thus is very sensitive to constructive imperfections that, in general, cause loss of prestressing. This paper presents the analysis on a viaduct constructed in Rio de Janeiro, with external prestressed concrete, where it was observed, after four years in service, some join opening, what indicates decompression of concrete. Several studies have been worked out, emphasizing among them the test for the measurement of natural frequencies of the prestressed tendons. This procedure allows getting the real state of stresses in those reinforcements through the method of vibrant rope. Measurements of join opening for a known load were also done, providing another way to determine the stress level in the tendons. Finally these results are compared with the theoretical prestressing force required for the project according to NBR6118-2003 [1] practice code. Finally, a discussion is presented to point out the possible causes of the decompression referred above.