Reliability verification of an existing reinforced concrete slab

The submitted contribution provides background information on the principles accepted in the CEN Technical Specification (TS). The application of the verification methods provided in the TS is clarified by an assessment of a reinforced concrete precast panel. The panel provides insufficient resistance in comparison to that required by Eurocodes for design of new structures. The critical comparison of the reliability levels indicated by Eurocodes, the assessment value method, and fully probabilistic approach demonstrates the benefits gained by applying the principles of the TS. While the partial factors recommended in Eurocodes leads to a negative result the assessment value method and the probabilistic method indicate sufficient structural reliability

Reliability of a structure stricken by a tornado

A tornado may become a very dangerous climatic action for any structure, depending on the tornado intensity and extent of the structure. The origin of a tornado, its range and further activity appear to be unpredictable and completely random. The strike of a tornado to a structure depends on the tornado movement and the structure extent. The tornado intensity is specified by the wind speed, following observed damages and consequences. The probability of a tornado strike on a structure depends on the extent of the structure itself, on the tornado range, and the extent of the considered reference area, for which data concerning tornado appearance are available. The probability of failure of a structure is given by the product of the probability of contact of a tornado with the structure and the probability of exceeding the design speed of the tornado wind. The probability of exceeding the design wind speed depends on the assumed distribution of wind speed and the frequency of tornadoes during the required lifetime of the structure. The target failure probability of common structures presented in available documents is 10−6 per year, and 10−7 per year of structures in power plants. However, it is not clear how these criteria have been derived. Further development of reliability theory of tornado-stricken structures is recommended to be focused on the risk analysis of appropriate systems, of which the considered structures are elements, on the target failure probability, on detailed analysis of the probability distribution of tornado wind speed and their frequency during the required lifetime of the structures

Assessment of fatigue degradation and service life of power-producing equipment

Cyklická únava materiálů významně ovlivňuje degradaci a celkovou životnost energetických zařízení v elektrárnách. Současné postupy hodnocení únavových jevů uváděné v nových mezinárodních předpisech ISO a CEN vycházejí z koncepce S-N křivek únavových vlastností materiálů a Palmgren-Minerova pravidla kumulace poškozování. Nejistoty únavových vlastností energetických zařízení a účinků zatížení se podchycují dílčími součiniteli, které je nutno stanovit individuálně s ohledem na skutečné podmínky zařízení.Příspěvek byl zpracován v rámci řešení Národního centra pro energetiku TN010000007, Segmentu 1, PB1.16. Vývoj nástrojů predikce technického stavu zařízení elektráren a tepláren podporovaného Technologickou agenturou České republiky.Cyclic fatigue of materials significantly affects the degradation and service life of powerproducing equipment. The present procedures of fatigue assessment provided in new international documents ISO and CEN are based on S-N curves of material properties and the Palmgren-Miner rule for accumulation of the fatigue damage. Uncertainties in fatigue properties of the equipment and in load effects are conveyed by the partial factors that should be specified individually considering actual conditions of the equipment

Assessment of components service life in power industry

Uvedené operativní postupy hodnocení životnosti energetických zařízení navazují na nový evropský dokument pro hodnocení existujících konstrukcí, který vychází z mezinárodní normy ISO, na evropské předpisy CEN i na další mezinárodní dokumenty. Příspěvek zahrnuje pokyny pro hodnocení životnosti všech druhů zařízení vystavené libovolnému zatížení a příklady stanovení zbytkové životnosti zařízení v elektrárnách.This work was supported by the Ministry of Culture of the Czech Republic under Grant DG16P02M050 “Optimisation of Observations and Assessment of Heritage Structures”.Presented operational rules for assessment of components service life are closely linked to International Standards ISO, to new European document CEN on assessment of existing structures and to further international documents. The contribution covers instructions for assessment of all kinds of components exposed to arbitrary actions and examples of assessing remaining working life of components in power industry

Modelové nejistoty smykové odolnosti železobetonových nosníků se smykovou výztuží podle EN 1992-1-1

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.Příspěvek se zaměřuje na modelové nejistoty smykové odolnosti železobetonových prvků se smykovou výztuží s využitím dostupných experimentálních dat. Analyzuje se závislost modelové nejistoty na základních veličinách pro výpočet smykové únosnosti podle EN 1992-1-1. Jsou identifikovány veličiny významně ovlivňující modelovou nejistotu. Pravděpodobnostní rozdělení modelové nejistoty je lognormální s variačním koeficientem 0.25 a různými průměrnými hodnotami závislými na odolnosti smykové výztuže

Target reliability levels in present standards

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 lif

Reliability and risk acceptance criteria for civil engineering structures

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

Nejistoty smykové odolnosti železobetonových nosníků s třmínky – porovnání postupů podle EN 1992-1-1 a fib MC 2010

The submitted contribution is focused on the model uncertainty related to shear resistance of reinforced concrete beams with stirrups. Using available test results, effects of basic variables on the model uncertainty are analysed. Considering the section-oriented models provided in EN 1992-1-1 and in the new fib Model Code 2010 are critically compared. Proposed probabilistic description of the model uncertainty consists of the lognormal distribution having the mean and coefficient of variation dependent on the considered model. Strength of shear reinforcement seems to be the most important basic variable for most of the considered models.Příspěvek je zaměřen na modelové nejistoty smykové odolnosti železobetonových prvků s třmínky. S využitím dostupných experimentálních dat se porovnávají nejistoty modelů v EN 1992- 1-1 a fib Model Code 2010. Jsou identifikovány veličiny významně ovlivňující modelovou nejistotu. Teoretický popis nejistot se opírá o lognormální rozdělení s průměrem a variačním koeficientem závislým na použitém modelu. Pro většinu uvažovaných modelů je pevnost smykového vyztužení nejvýznamnější základní veličinou

Reliability of existing reinforced concrete slabs exposed to punching shear

Selected standardised models for the verification of punching shear in reinforced concrete structures are applied for the probabilistic assessment of their reliability level. It appears that the models given in EN 1992-1-1 and prEN 1992-1-1 lead to more realistic estimates of the reliability level of existing reinforced concrete members with respect to punching shear than the models recommended in some national codes. The controlled perimeter has significant influence on the results and should be harmonized in prescriptive documents