Miroslav Sýkora

Assessment of Flooding Risk to Cultural Heritage in Historic Sites

Fluvial flooding in August 2002 affected a number of structures in the Czech Republic. Considerable damage was observed particularly in the historic city of Prague. Extensive investigations indicated that main observed causes of damage could be classified into geotechnical aspects, inadequate structural properties, and insufficient communication. After the flooding responsible authorities have considered permanent and temporary protective measures to reduce adverse consequences of flooding in the future. Decisions concerning expensive measures should be preferably based on risk optimization, taking into account potential societal and economic consequences and losses of cultural heritage values. General framework of the risk assessment is thus proposed considering specific issues of cultural heritage. Such an assessment needs a theoretical model suitable for predicting flows and extents of future floods. For that reason, the authors statistically analyzed hydrologic data for annual maximum flows of the Vltava River in Prague dating back to 1827. Pearson III and lognormal distributions seem to be suitable models for a considered sample. Estimations of extreme flows, needed for assessment of flooding risk to endangered sites and decisions on protective measures, are provided for different return periods.

Assessment of Uncertainties in Mechanical Models

Resistances of mechanical systems are primarily dependent on material properties, geometry and uncertainties associated to an applied resistance model. While materials and geometry can be relatively well described, the resistance model uncertainty is not yet well understood. The present contribution proposes a general concept of the model uncertainty. Factors affecting results obtained by tests and models and influences of actual structural conditions are overviewed. Application of theoretical principles is illustrated by an example of historic iron columns considering a simple mechanical model. Proposed probabilistic description of the model uncertainty consists of the lognormal distribution having the mean 1.35 and coefficient of variation of 0.12.

Target Reliability Levels in Present Standards

Abstract The target reliability levels recommended in national and international documents vary within a broad range, while the reference to relevant costs and failure consequences is mentioned only very vaguely. In some documents the target reliability index is indicated for one or two reference periods (1 year, 50 years or life-time) without providing appropriate links to the design working life. This contribution attempts to clarify the relationship between the target reliability levels, costs of safety measures, failure consequences, reference periods and the design working life

Evaluation of Compressive Strength of Historic Masonry Using Measurements

Historic structures are made of different types of masonry with significantly different properties. As a rule the information on mechanical properties of masonry components has to be obtained by testing. Estimation of masonry strength from measurements with due regard to relevant uncertainties may be a key issue of the reliability assessment. The probabilistic model of masonry strength is developed considering uncertainties in basic variables and testing procedures. It appears that the characteristics of masonry strength can be well estimated using fundamental statistical methods.

MODEL UNCERTAINTY FOR SHEAR RESISTANCE OF REINFORCED CONCRETE BEAMS WITH SHEAR REINFORCEMENT ACCORDING TO EN 1992-1-1

Abstract The submitted contribution is focused on the model uncertainty related to shear resistance of reinforced concrete beams with special shear reinforcement considering available test results. Variation of the model uncertainty with basic variables is analysed and significant variables are identified for the section-oriented formula provided in EN 1992-1-1. Proposed probabilistic description of the model uncertainty consists of the lognormal distribution having the coefficient of variation of about 0.25 and the mean significantly varying with the strength of shear reinforcement

Bayesian network application for the risk assessment of existing energy production units

A Bayesian network is applied in this contribution in order to assess the risks of a selected production unit in a fossil power station. A general framework for the risk assessment of production units of a power station is presented first by implementing statistical methods and Bayesian networks. Special emphasis is given to the input data consisting of failure rates which are obtained on the basis of recorded data and expert judgements. The consequences of failure are divided into economical and human (societal): economic consequences include outages of key technological devices, societal consequences cover potential injuries and fatalities. Probabilistic risk assessment methods are applied to the selected production unit of a power station. The influence of the uncertainties in the considered technical parameters on the availability of the unit is assessed and the acceptance of the calculated availability represented through the mean value and the standard deviation is discussed. Societal risks given in terms of weighted injuries and fatalities are obtained and respective risk acceptance criteria are presented. Uncertainties affecting the risks are discussed. It appears that the proposed framework provides a valuable assessment of the influence individual devices and their components on availability and societal risk. For that purpose the used methodology, intentionally simplified for operational applications, includes important factors affecting risks of production units. It is concluded that Bayesian networks are a transparent method for the probabilistic risk assessment of complex technological systems. The results of the performed analyses can be easily updated when additional information becomes available as illustrated in characteristic examples.

Reliability and Risk Acceptance Criteria for Civil Engineering Structures

Abstract The specification of risk and reliability acceptance criteria is a key issue of reliability verifications of new and existing structures. Current target reliability levels in standards appear to have considerable scatter. Critical review of risk acceptance approaches to societal, economic and environmental risk indicates that an optimal design strategy is mostly dominated by economic aspects while human safety aspects need to be verified only in special cases. It is recommended to specify the target levels considering economic optimisation and the marginal life-saving costs principle, as both these approaches take into account the failure consequences and costs of safety measures.

Strength assessment of historic brick masonry

AbstractThe identification of residual service life of a structure is an exceptionally demanding task in the case of reconstructed or newly modernised buildings. The identification of residual service life requires the study and knowledge of the mutual interaction of a building with its external environment, in particular, the time variable effects and impacts which lead to degradation processes and phenomena affecting and, in the absolute majority of cases, degrading the physical, mechanical and other properties of materials and structures. The article presents the results of in-situ and laboratory research of strength parameters of masonry from the start of the 20th century applying destructive and non-destructive tests. Besides, a probabilistic model and a procedure for the determination of masonry strength are described. It appears that the probabilistic approach leads to a design value by ca 5% higher than the deterministic approach.

Estimating design resistance of wrought balcony girders

Abstract The contribution is focused on reliability of balcony girders of a Czech national heritage monument. As preliminary reliability assessment suggests insufficient resistance, a series of nondestructive tests supplemented by a single tensile test are performed and evaluated by the statistical methods. Values of material properties, recommended in standards for historic materials, seem to be overly conservative and it is advised to specify properties of historic metallic materials by tests.

Updating in the Probabilistic Assessment of Existing Structures / Pravděpodobnostní Aktualizace Při Hodnocení Existujících Konstrukcí

Abstract Assessment of existing structures should be based on the knowledge about as-built conditions including uncertainties concerning geometry, material properties, loading and environmental conditions. A crucial step of the assessment may be the evaluation of prior information and newly obtained measurements for which Bayesian approach provides a consistent framework. Updating of probabilistic distributions of basic variables, direct updating of failure probability and combination thereof can be applied. Abstrakt Při hodnocení existujících konstrukcí je potřebné uvážit nejistoty související s geometrickými a materiálovými vlastnostmi, zatíženími a vlivy okolního prostředí. Důležitým krokem hodnocení může být využití apriorních znalostí společně s nově získanými informacemi o konstrukci. Bayesovské postupy umožňují aktualizovat pravděpodobnostní rozdělení základních veličin nebo přímo pravděpodobnost poruchy.