Target reliability for existing structures considering economic and societal aspects

Sýkora, Milan; Diamantidis, Dimitris; Holický, Milan; Jung, Karel

doi:10.1201/9781351204590-16

Cited by 13 publications

(20 citation statements)

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“…Considering the model uncertainty characteristics given in Table for Level III, the variation of model uncertainty factor with target reliability is displayed in Figure for beams with stirrups and α R = 0.32, that is, “non‐dominant resistance variable” according to ISO 2394 and fib bulletin 80 . The range of β represents the target lifetime levels commonly associated with the Ultimate Limit States for new and existing structures …”

Section: Discussionmentioning

confidence: 99%

Uncertainty in shear resistance models of reinforced concrete beams according to fib MC2010

Sýkora

Krejsa

Mlčoch

et al. 2018

Structural Concrete

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Load bearing capacity can be predicted by appropriate modeling of material properties, geometry variables, and uncertainties associated with an applied model for the failure mechanism under consideration. The submitted study investigates shear resistance model uncertainties for reinforced concrete beams with and without shear reinforcement, considering large test databases and various levels of approximation offered by fib Model Code 2010. Model uncertainty is treated as a random variable and its characteristics are obtained by comparing test and model outcomes. The sensitivity of model uncertainty with respect to basic variables is analyzed. For beams with stirrups, Level III is recommended for practical applications. Its predictions are shown to be independent of the amount of shear reinforcement and have reasonable bias and dispersion around test results. For beams without shear reinforcement, the use of Level II is advisable and a distinction between lightly reinforced and moderately to heavily reinforced beams should be made. K E Y W O R D S fib model code 2010, model uncertainty, partial factor, reinforced concrete, shear reinforcement, shear resistance 1 | INTRODUCTIONAdequate description of the uncertainties in resistance models was recognized as one of key issues in reliability investigations of new and existing reinforced concrete (RC) structures. 1 Particularly when description of load effects and structural responses is highly complex, and operational procedures are based on simplified approaches, model uncertainty may dominate structural reliability and its quantification and explicit inclusion in reliability analysis is required. 2 Such cases can be identified by the lack of consensus amongst experts; alternative models used in research studies and practical applications; and different levels of approximation (LoA) 3 introduced in design codes. This is the case with shear resistances of RC structures, recognizing that shear strengths predicted by different design codes for a particular beam or section can vary by factors of more than two. 4 Shear resistances of beams have stimulated an extensive debate over recent decades, as there is not yet an international consensus on which variables are important, 5 which mechanisms govern 6,7 and how to codify existing understanding. 8 Features of several models for shear resistances of beams with and without special shear reinforcement (hereafter referred to as "shear models" for brevity) were investigated and improvements proposed. [9][10][11][12][13][14][15] The complexity of shear transfer actions and modeling was recognized and described in detail in References 16,17.Model uncertainty as an indicator of the difference between model and real structural resistances was explicitly addressed by Russo et al 10 who analyzed the uncertainty associated with the models in EN 1992-1-1 18 and American Concrete Institute (ACI) 318M-08. 19 Bentz et al 4 were focused on the ACI procedure and two approaches belonging to the Modified Compression Field Theory. The recent

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Section: Discussionmentioning

confidence: 99%

Uncertainty in shear resistance models of reinforced concrete beams according to fib MC2010

Sýkora

Krejsa

Mlčoch

et al. 2018

Structural Concrete

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“…where R is the structural or local resistance, and S is the action or action effect of permanent loads (G), prestressing (P), and variable loads (Q). This condition has to be satisfied for a certain level of probability defining the desired safety level; see, for instance, ISO 2394, 22 JCSS, 23 and NKB 24 for proposed safety levels and Melchers, 25 Stewart et al, 26 and Sykora et al 27 for how the knowledge about the structure and economical, societal and environmental risks associated with it can be accounted for defining the safety level. According to Model Code 2010, 20 the verification of the required level of structural safety should follow a probability-based concept.…”

Section: Safety Verificationmentioning

confidence: 99%

Demonstration and examination of a procedure for successively improved structural assessment of concrete bridges

Bagge

2019

Structural Concrete

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Assessing the load‐carrying capacity of existing bridges is an important infrastructure management task. In order to support the structural assessment of concrete bridges better, a procedure has been proposed, based on successively improving the bridge analysis. A multilevel strategy for structural analysis has been combined with concepts for verification of the desired safety margin, thus providing tools for engineers to model the structural behavior of bridges more accurately when necessary. This paper describes the procedure as applied to a prestressed concrete girder bridge, with use of experiences from the previous failure tests and associated evaluations of the bridge. Initial structural assessment indicated the critical failure mode to be due to shear in one of the girders; however, the enhanced analysis showed a complex failure involving both the girder and the bridge deck slab. Improving the structural analysis using nonlinear FE analysis for the loading initially identified as critical, increased the permitted axle loads on the bridge to 12 to 14 times those given by traditional and standardized assessment methods, depending on the concept used for safety verification. The model uncertainty was crucial for the verification of the structural safety and has to be properly taken into account. However, there are few recommendations, with regard to model uncertainties, on the application of nonlinear FE analysis, and detailed guidelines should be used for the modeling procedure in order to reduce analyst‐dependent variability in the results. The presented study demonstrates the applicability and the advantages of using the proposed procedure for successively improved analysis for bridge assessment.

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“…The reduction can be assessed by implementing the values associated to the higher category of relative cost of safety. A practical reduction of the target value by 0.5 for existing structures compared to new designs has been recommended in [21], [23]. Also, a minimum target reliability, below which the structure should be upgraded, is proposed in [22], [23].…”

Section: Existing Versus New Structuresmentioning

confidence: 99%

Reliability differentiation and uniform risk in standards: a critical review and a practical appraisal

Diamantidis¹,

Sýkora²

2019

Future Trends in Civil Engineering

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Reliability of structures and infrastructures is a major issue in structural engineering. Structural standards have traditionally been mainly concerned with public safety preventing loss of life or injury; this view has been shifting in recent years towards minimisation of economic loss. This contribution discusses the reliability differentiation principle in modern standards. Its aim is to achieve uniform risk levels for the various classes of structures. Codified criteria for reliability differentiation and risk informed decisions inherent in standards and especially in the Eurocodes are critically reviewed. It is shown that the classification of structures based on consequences of failure is an approach that has not been widely implemented in everyday design. Practical rules for the classification and implementation in design are needed and related proposals are presented.

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Target reliability for existing structures considering economic and societal aspects

Cited by 13 publications

References 0 publications

Uncertainty in shear resistance models of reinforced concrete beams according to fib MC2010

Uncertainty in shear resistance models of reinforced concrete beams according to fib MC2010

Demonstration and examination of a procedure for successively improved structural assessment of concrete bridges

Reliability differentiation and uniform risk in standards: a critical review and a practical appraisal

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