You are here:

Daniela Tavera Diaz

Date and time: 08-10-2021

Track: Structural Engineering

Topic: Validation of a Newly Proposed Global Factor Method Applied in the Assessment of Reinforced Concrete Structures Modelled by NLFEA

Description: Nowadays, one of the main requirements from civil engineering structures is the level of reliability and safety that they must provide to the users. In structural analysis, the exponential application of numerical methods, as the nonlinear finite element analysis (NLFEA), is due to the increasing growth of computational power. These powerful tools provide the opportunity to study the global behavior of complex systems. The latter is especially relevant for cases where nonlinearities highly impact the performance of the structure. However, to ensure a certain level of safety, the stochastic nature of all the influencing parameters must be accounted for during the analysis and design stages. The latter is precisely the role of Safety Formats: a mathematical procedure to ensure an imposed level of reliability while computing the design resistance of structures. Several existing safety formats have been implemented along with the NLFEA in the structural reliability assessment of reinforced concrete structures. Nonetheless, these formats face some criticism in their usability due to some of the assumptions implied in their derivation. Therefore, Monti et al. (2021) recently proposed a safety format: a new Global Factor Method (GFM) that aims to be applicable in the nonlinear finite element analysis of reinforced concrete structures with concurrent failure mechanisms influencing the global performance at a predefined limit state. In a general description, the method requires the output obtained from two nonlinear finite element analyses and the calculation of a Global Safety Factor related to the resistance of the whole structural system. This thesis aims to provide scenarios to validate the new safety format for its future implementation in codes and the industry since, currently, they are extremely limited. Therefore, the GFM is implemented in three overall case studies with increasing levels of complexity, divided into two reinforced concrete cross-sections, and three simply supported beams. During the case studies, special attention is given to the size of the perturbation (described by the so-called $c$ parameter) that proportionally decreases the basic variables for the second nonlinear analysis. Several Engineer Decision-based Scenarios are applied when choosing the Critical Local Failure Mechanisms and the related basic variables to be perturbed. Finally, it is found that the method provides reliable resistance for structures with a single failure mechanism. However, for structures modelled with continuum elements where two concurrent failure mechanisms lead to global failure, the GFM still needs to be revised to provide more accurate guidelines and reduce the space for decisions made by the analyst that highly impact the performance of the method. These decisions are related to identifying and locating the LFM and their basic variables, selecting the solution strategy implemented in the NLFEA, and choosing a suitable modelling uncertainty. At this point, the application of the method demands an experienced analyst and several parametric studies regarding all those decisions, which reduces its efficiency in terms of engineering and computational time.

Location: CEG Faculty