Reliability study of the ductility of reinforced concrete beams based on the NBR 6118 (2014)

Resumo

Semi-probabilistic methods are the procedures used in most structural design codes to try to ensure the
safety of structures. However, there are several uncertainties related to the structural models, as well as
uncertainties in the loads, in the geometric properties of the elements and in the mechanical properties of the
materials employed. Therefore, it becomes necessary to apply probabilistic methods to verify safety, and structural
reliability methods appear in this scenario as a way to calculate probabilities of failure taking into account the
uncertainties involved. Several studies were developed about the reliability related to the strength of reinforced
concrete beams. However, reliability analyzes focusing on the ductility of these structural elements are still rare in
the literature. In the present paper it is intended to determine the level of reliability related to the ductility of
reinforced concrete beams designed in accordance with the Brazilian code for the design of reinforced concrete
structures (NBR 6118). For this, an analytical model which tries to adequately represent the non-linear behavior
of the beams is implemented. To evaluate the structural reliability, a limit state function based on strains in the
tensile rebar is presented. A code in MATLAB is developed, in which the Monte Carlo simulation is implemented
and a beam is evaluated for a rage of concrete strength from 20 to 90 MPa. From this study, it is concluded that in
some cases the reliability related to ductility can be considered low.