This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Authors are actively involved in the technical committees preparing the new Eurocodes for reinforced concrete design as well as the new fib model code 2020. The simulation by nonlinear analysis is being used by engineers for the design of reinforced concrete structures, but until recently no suitable safety formats were available. The first concise treatment of this problem has been developed in the international fib model 2010. An important aspect of the reinforced concrete design by simulation is a due estimation of model uncertainties, which are inherently strongly dependent on the software, the numerical approach and the user. A typical feature of the simulation-based design is the global safety format, which is different from a sectional local check in the standard design approach.



The sources of uncertainty in the reliability analysis are of two kinds, an aleatory uncertainty of material properties, which can be described by probabilistic models and an epistemic uncertainty of models reflecting a lack of knowledge. The global design formats with different levels of probabilistic approximation are discussed and compared.



A general method for the assessment of the model uncertainty is proposed and an example is presented for a particular resistance model. A set of 33 laboratory tests of reinforced concrete elements by other authors are used for the model validation and for the determination of the model uncertainty. It covers a wide range of failure modes of concrete structures, from brittle to ductile, and the member cross section sizes ranging from 0.1 to 4 m. This means that a size effect is well reflected as well. The numerical model used for the simulation is the fracture-plastic constitutive model for concrete developed by the authors and implemented in a nonlinear finite element analysis commercial software. The proposed method can be used as a general framework for the calibration of the model uncertainty factor to be used within the framework of the global safety formats for reinforced concrete design based on numerical simulation.



The description of the general method for the treatment of epistemic model uncertainties is illustrated on examples from engineering practices, such as design of offshore windmill structures and reinforced concrete buildings. The paper summarizes the experience of the authors obtained in recent years in various projects involving the application of nonlinear finite element analysis and the new safety formats from Model Code 2010 (Cervenka V. 2013).