Structural reliability of strengthened reinforced concrete beams: comparative study of different design methods

Resumo

There are some methods in the literature for the design of concrete jackets for beams and they differ in
the way they represent the structural behavior of the beam cross-section. As a consequence, it is possible to obtain
different results for a flexure strengthened beam. This scenario raises doubts about what are the consequences of
adopting different hypotheses. In the present study, two methods from the literature for strengthening design with
jackets were compared. The first considers a monolithicy factor that reduces the beam resistance, while the second
considers the compression steel contribution to resistance. The strengthened sections were analyzed using the First
Order Reliability Method. Information about the random variables limit state functions involved were obtained
from the literature. Ten experimental strengthened beams available in the literature were selected to apply the
design methods and to perform the reliability analysis. The strengthening design and reliability analysis routines
were implemented in the Matlab environment. The results indicate that the first method, the one that considers a
monolithicy factor, results in a larger steel reinforcement area for the strengthening. Also, the reliability analyses
shows that the different parameters considered in each design method have a significant impact in the reliability
index.