Advanced constitutive models implemented in the finite element system ATENA serve as rational tools to explain the behaviour of connection between steel and concrete. Three nonlinear material models available in ATENA are described: crack band model based on fracture energy, fracture-plastic model with non-associated plasticity and microplane material model. Nonlinear simulation using these advanced constitutive models can be efficiently used to support and extend experimental investigations and to predict behaviour of structures and structural details.

The concept presented for the safety assessment of concrete structures integrates nonlinear finite element analysis with stochastic and reliability technology into an advanced engineering tool. The basic aim of the stochastic nonlinear analysis is to calculate the safety index of an existing engineering structure, which characterizes its reliability (and failure probability). The nonlinear solution enables a realistic estimation of the structural response statistics to be obtained (failure load, deflections, cracks, stresses, etc.). The possibility of randomization for such computationally intensive problems is shown. Latin hypercube sampling is used in order to keep the number of required simulations at an acceptable level. Statistical correlation, which is important for a realistic solution, is imposed by using a stochastic optimization technique called simulated annealing. The sensitivity of results to random input parameters can be evaluated using nonparametric rank-order correlation coefficients. The safety index of the analysed structure is calculated from the stochastically obtained structural resistance and expected load distribution using appropriate reliability techniques. The presented approach for the safety assessment of engineering structures supersedes the usual methods based on simplified formulas. It can lead to considerably improved results since the structure is analysed more precisely. Therefore, it supports a higher level of decision-making process in bridge administration and maintenance of transport macrostructure.

A large beam tested at Toronto University for a prediction contest was simulated by the authors using a nonlinear finite element code. Their entry was chosen as the overall winner of the prediction contest and was a motivation for this case study. The crack propagation was modeled by a smeared crack approach and a fracture mechanics-based cohesive crack model. The paper discusses the model sensitivity to mesh sizes and fracture parameters. A parameter study was performed to examine the model uncertainty of numerical simulation. A probabilistic model of concrete non-homogeneity was used to reflect a more realistic strain localization in the smeared crack model.

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