Jan Podroužek

SPATIAL DEGRADATION IN RELIABILITY ASSESSMENT OF AGEING CONCRETE STRUCTURES

Presented paper concerns the difficulty of objective characterization of spatial variability due to advancing degradation as a result of environmental exposure. The main issue is to enhance realism in the prediction of remaining service life of existing concrete infrastructure and thus effectively cover the relatively large sample space of possible future deteriorating states. This is done by introducing a special sampling strategy where artificial realizations of damage scenarios are generated. Here, not only material and geometry of a particular structural member is randomized in a nonlinear 3D finite element context, but advanced evolutionary spatial degradation models are applied to account for the variability of future damage states. These are computed using a non-traditional evolutionary scheme based on cellular automata (CA), which is used here to solve the transport equations in time and space and generate the irregular and heterogeneous structure of concrete. Within the presented example of an ageing bridge, the CA simulation also accounts to complex boundary conditions, e.g. the non-stationary seasonal de-icing salt application, irregular turbulent feed or washout effects. The selected case study of an existing deteriorated bridge serves as an application example with historical evidence and well documented damage profiles. It is further discussed with respect to Monte Carlo based structural reliability assessment, how to infer likelihoods associated to the set of implicit statements on damage, as this concept still offers open questions for research, yet is critical to successful and objective uncertainty quantification.

Modeling of Environmental Effects on Bridge Components: Possibilities of Cellular Programming

The early deterioration of concrete structures due to the effects of external aggressive environment is well known. This paper presents cellular automata approach to the problem of lifetime assessment of concrete structures, particularly bridges, under the diffusive attack of external aggressive agents. The diffusion process is modeled by cellular automata technique as a 2D task describing more realistically the spatial variability of e.g. the chloride ingress within dynamic environment. The effectiveness of the proposed methodology arises from the transparent implementation yet complex behavior of two selected numerical case studies.

Robust Power Law Extrapolation for Adhesive Anchors Under Sustained Load

Post-installed adhesive anchors play an important role in modern construction. As with many structural products, adhesive anchors must undergo rigorous testing to verify serviceability and ultimate performance characteristics under job-site-relevant conditions before being used in real projects. The check of long-term performance under sustained load is based on extrapolation from experimental short-term creep data approximating the creep mechanism of the entire anchor system with a power law model as detailed, for example, in ACI 355.4 and ETAG 001. These normative guidelines are critically reviewed from a scientific as well as practical point of view. Based on the presented evidence, specific recommendations for anchor testing and assessment guidelines are proposed.

RANDOM AND GRADIENT BASED FIELDS IN DISCRETE PARTICLE MODELS OF HETEROGENEOUS MATERIALS

The proper characterization of the microstructure and macroscopic properties of random heterogeneous materials may help to interpret the observed scatter in many engineering problems. In this contribution, a lattice discrete particle model is presented in a civil engineering framework with a special emphasis on concrete structures and infrastructure. The implications of spatial variability are investigated with regard to the observed scatter in standard concrete tests. In particular, classical experiments, such as three-point bending tests, may exhibit various levels of scatter which have to be accounted for if material characteristics are to be derived from such experiments and consequently used for the analysis and design of structural systems. Therefore, random and gradient based fields are combined in this paper in an attempt to realistically capture the material properties and associated variability stemming from the microstructure and macroscopic features such as the placement of coarse aggregates. Various mechanical and statistical aspects of simulated test series are investigated, such as macroscopic fracture energy or distribution of load bearing capacity. The presented application example of three-point bend specimens incorporates not only the inherent spatial variability owing to the placement of aggregates, modelled by random fields, but also various production artefacts, such as concrete compacting characterized here by gradient based fields. 605 Available online at www.eccomasproceedia.org Eccomas Proceedia UNCECOMP (2017) 605-615 ©2017 The Authors. Published by Eccomas Proceedia. Peer-review under responsibility of the organizing committee of UNCECOMP 2017. doi: 10.7712/120217.5396.16710 Jan Podroužek, Jan Vorel, and Roman Wendner

Virtual 3D Nonlinear Simulation of Uniaxial Tension Test of Concrete

The paper shows possibilities of nonlinear fracture mechanics simulation to capture results of uniaxial tension experiments and discuss problematic aspects of modelling. The occurrence of secondary flexure is a fundamental problem studied experimentally by third author [1]. The virtual 3D numerical simulation of those experiments eliminating/leaving secondary flexure was performed. The aim of modelling is to give a better insight into uniaxial tension behavior which cannot be obtained directly from experiments including the formation of fracture process zone, the influence of load eccentricity and heterogeneity of concrete.