STRUCTURAL OPTIMIZATION OF HYPERSTATIC REINFORCED CONCRETE BEAMS CONSIDERING THE SYSTEM RELIABILITY

Resumo

Civil engineering structures are inevitably under uncertainties, constituted by multiple
components, and also subjected to several failure modes. Thus, the design could be made considering
the global system reliability, the correlation between failure modes, and also the correlation between the
failure of its components, defining where it is worth spending more or less material. Thereby, a system
component with little influence over the system reliability could be designed with less reliability, for
instance. However, regarding reinforced concrete structures, the current Brazilian normative that guides
its design presents very few techniques intending to avoid the progressive collapse. Moreover, it
stablishes that the structural system is obtained after the individual design of each of its structural
elements, without any consideration of the system reliability. Aiming to analyze the optimal designs of
usual structural systems, the Reliability Based Design Optimization (RBDO) is performed on a
hyperstatic beam of reinforced concrete while considering the system reliability as a constraint. Optimal
parameters are usual design variables, such as the height of the beam and the concrete compressive
strength. In order to better represent the physical and geometrical nonlinearities involved, a finite
element approach based on positions is used herein. The obtained optimal designs are compared to those
acquired by the semi probabilistic approach proposed by the current Brazilian normative. Results of a
preliminary example shows that the RBDO leads to a more economical results while maintaining the
desired target reliability.