No abstract

When performing non-linear finite element analyses during the design of large reinforced concrete structures, there is a need for a general, robust and stable solution strategy with a low modelling uncertainty which comprises choices regarding force equilibrium, kinematic compatibility and constitutive relations. In this paper, analyses of experiments with a range of structural forms, loading conditions, failure modes and concrete strengths show that an engineering solution strategy is able to produce results with good accuracy and low modelling uncertainty. The advice is to shift the attention from a detailed description of the postcracking behaviour of concrete to a rational description of the pre-cracking compressive behaviour for cases where large elements are used and the ultimate limit capacity is sought.

In order to make non-linear finite element analyses applicable during assessments of the ultimate load capacity or the structural reliability of large reinforced concrete structures, there is need for an efficient solution strategy with a low modelling uncertainty. A solution strategy comprises choices regarding force equilibrium, kinematic compatibility and constitutive relations. This contribution demonstrates four important steps in the process of developing a proper solution strategy: 1) definition, 2) verification by numerical experiments, 3) validation by benchmark analyses and 4) demonstration of applicability. A complete solution strategy is presented in detail, including a fully triaxial material model for concrete, which was adapted to facilitate its implementation in a standard finite element software. Insignificant sensitivity to finite element discretization, load step size, iteration method and convergence tolerance were found by numerical experiments. A low modelling uncertainty, denoted by the ratio of experimental to predicted capacity, was found by comparing the results from a range of experiments to results from non-linear finite element predictions. The applicability to large reinforced concrete structures is demonstrated by an analysis of an offshore concrete shell structure.

Advanced numerical modelling of high-strength concrete ( c > 60 MPa) structures designed to withstand severe thermal conditions requires detailed and reliable information on the mechanical properties of the material exposed to elevated temperatures. The only uniaxial compressive strength variation with temperature is not enough to satisfy the big number of parameters often required by advanced non-linear constitutive models.For this reason, a complete experimental investigation is required. The paper takes a commonly used high strength concrete ( c = 73 MPa) as an example to describe a comprehensive experimental approach instrumental to the parameter definition and calibration of common constitutive models for concrete. The present study not only studied the overall compressive and tensile behaviour of the case study material, but also investigated the effect of elevated temperatures on the specific fracture energy and the evolution of internal damage, in residual conditions after a single thermal cycle at 200, 400 and 600 °C.