Břetislav Teplý

FReET: Software for the statistical and reliability analysis of engineering problems and FReET-D: Degradation module

Abstract The objective of the paper is to present methods and software for the efficient statistical, sensitivity and reliability assessment of engineering problems. Attention is given to small-sample techniques which have been developed for the analysis of computationally intensive problems. The paper shows the possibility of “randomizing” computationally intensive problems in the manner of the Monte Carlo type of simulation. In order to keep the number of required simulations at an acceptable level, Latin Hypercube Sampling is utilized. The technique is used for both random variables and random fields. Sensitivity analysis is based on non-parametric rank-order correlation coefficients. Statistical correlation is imposed by the stochastic optimization technique – simulated annealing. A hierarchical sampling approach has been developed for the extension of the sample size in Latin Hypercube Sampling, enabling the addition of simulations to a current sample set while maintaining the desired correlation structure. The paper continues with a brief description of the user-friendly implementation of the theory within FReET commercial multipurpose reliability software. FReET-D software is capable of performing degradation modeling, in which a large number of reinforced concrete degradation models can be utilized under the main FReET software engine. Some of the interesting applications of the software are referenced in the paper.

Durability assessment of concrete structures: reinforcement depassivation due to carbonation

This paper deals with durability design and comments on the assessment of reinforced concrete (RC) structures in relation to existing codes. Enhancement is provided by advanced approaches incorporating probabilistic simulations, mathematical models of the carbonation process in concretes made from CEM I through to CEM V, and the reliability issue. This paper presents practical software tools used for service life prediction, concrete cover evaluation and assessment of relevant reliability levels. A partial verification using test results is also presented.

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.

Introduction to an Approach to Performing Sustainability Quantification of Concrete Structures

Efficient sustainability management requires the use of tools that enable the quantification, measurement or comparison of material, technological and construction variants. Tools of this kind which have been developed around the world in recent years include various indicators, indexes, etc. Generally, technical, economic, ecological and socio-cultural areas must all be included. Such a tool can be used as a powerful marketing aid and as support for the transition to the “circular economy”. Life Cycle Assessment (LCA) procedures are also used, alongside other approaches. LCA is a method that evaluates the life cycle of a structure from the point of view of its effect on the environment. Processes starting with the mining of mineral resources and including their transport, production and use up to their final processing as waste (recycling) are all taken into account. In addition, consideration is given to energy and raw material costs, and to environmental impact throughout the whole life cycle – e.g. through emissions. The presented contribution focuses on the quantification of sustainability connected with the use of various types of concrete with regard to their resistance against the effect of degrading influences. Sustainability factors are also determined using information regarding service life and “eco-costs”. The aim is to present a suitable methodology which can simplify decision-making concerning the design and choice of concrete mixes from a wider perspective, i.e. not only from the aspects of load-bearing capacity or durability.

Input Value Correlation in Chloride Ion Ingress Modelling and Concrete Structures Reliability

The assessment of service life of a structure can be performed via mathematical modelling – either analytical or numerical and it can be viewed as a necessary pre-requisite for life-cycle engineering decisions. Many works concerning the modelling and testing of degradation effects for engineering systems are reported in the literature. The present paper discusses the degradation modelling of reinforced concrete structures and concentrates on the damage they sustain due to chloride ingress, namely a special aspect: the influence of statistical correlation among input variables on the reliability.

Probabilistic Modelling and the k-Value Concept

The durability of concrete structures is an important issue. Eurocode EN 206-1 introduces the k-value concept for concretes made with supplementary cementitious materials; a prescriptive concept that recommends limiting water/cement ratio values for a specified exposure class. A more advanced performance-based concept directly requires that concrete be designed in terms of performance-related parameters, an approach which seems to be more suitable when durability must be achieved. The application of mathematical models in durability assessment is advocated, and an example is shown.

Probabilistic performance assessment of concrete structures subjected to corrosion process

In general, all structures are subjected to deterioration due to environmental and traffic actions over their life time. Maintaining an adequate safety level over their entire service life is thus not only an expensive task, but also filled with some level of uncertainty. Degradation in itself is not easily quantifiable because numerous aspects reduce the load bearing capacity of a structure. Furthermore, the development of actions over the multi-decade life time as well as the effects of preventive maintenance and rehabilitation measures is difficult to predict. For concrete bridges (chloride induced) reinforcement corrosion is in many cases the governing deterioration process, especially in regions where winter salt is commonly applied for traffic safety. This paper introduces a feasible approach to analyse the effects of chloride induced deterioration on the safety level, which is validated by the application to a real highway bridge. A probabilistic prognosis of the corrosion processes during the planned service life of the structure accounts for uncertainties in the experimental investigations, material properties and actions and provides the inputs for a long term performance assessment. In particular, comprehensive probabilistic analyses reveal the time dependent reliability levels with respect to code based serviceability and ultimate limit states.

How Reliable is the Durability of RC Structures

The goal of this paper is to show some trends and time profiles of the reliability index relevant to the Serviceability Limit State considering the design service life of RC structures. The interactive web page “RC_LifeTime” – originated by the authors – is used (see http://www.stm.fce.vutbr.cz/). The depassivation of reinforcing steel due to carbonation is considered conservatively as a limiting condition. It is based on model concrete carbonation with 12 random input variables; the Latin Hypercube Sampling simulation method is used. RC_LifeTime offers the following options: Service Life Assessment – a statistical evaluation of service life, where optionally the target value of reliability index s may be an additional input value and then the corresponding service life is the output value; Concrete Cover Assessment – a statistical evaluation of concrete cover value for the target service life, where optionally the required concrete cover value may be input in this case and the relevant reliability index s describes the reliability of reinforcement depassivation.

Safety of the Steam Generator Cover: A PSA Case Study

The loss of functionality of a steam generator cover is investigated in probabilistic terms and its safety measures are assessed. The goal is to make the inspection strategies for NPPs more realistic and efficient. Mathematical description of the gradual damage of the stud bolt until its rupture is based on the three stages: origin of a surface defect such as a crack or pitting; growth of defect before conditions stress corrosion cracking; growth of defect under stress corrosion cracking. The results of probabilistic safety assessment of the analyzed demountable connection of the 1st circuit collector of steam generator are presented