A quantification of the modelling uncertainty of non-linear finite element analyses of large concrete structures

The definition of design equations from semi-empirical or empirical models is a matter of fundamental importance in structural engineering. The direct application of partial safety factors for materials strength in such models is not appropriate in order to obtain design formulations coherent with some level of reliability, as empirical or semi-empirical formulations are calibrated adjusting empirical coefficients to fit a set of experimental data. Therefore, applying partial safety factors on material properties alone does not allow a correct estimation of structural reliability. In this paper, a reliability-based design bond strength relationship for tensed lapped joints and anchorages in reinforced concrete structures is derived applying a consistent reliability format. The semi-empirical model for mean laps and anchorages strength calculation proposed in fib Bulletin No 72 is studied. The probabilistic calibration of this model is performed defining the related model uncertainties, grounding on an extensive experimental database and distinguishing between new and existing structures. As a conclusion, the design expression for bond strength proposed by the authors is compared to current standards and its implications in laps and anchorage design in reinforced concrete structures are analyzed. K E Y W O R D Sbond strength, empirical and semi-empirical models, laps and anchorages, model uncertainties, structural reliability

Section: Determination Of Model Uncertainties For Laps and Anchoragesmentioning

confidence: 99%

Reliability‐based evaluation of bond strength for tensed lapped joints and anchorages in new and existing reinforced concrete structures

Mancini

Carbone

Bertagnoli

et al. 2017

“…It is noted that several recent studies discussed uncertainties in resistance models of concrete structural members for more complex failure modes, for instance: Rectangular columns subjected to axial force, bending moment, and shear force Shear strength of slender RC beams Corroded shear‐critical beams Slabs with plain bars and slabs on elastomeric bearings exposed to shear Beams and columns under combination of axial and shear forces and bending moments analyzed by advanced numerical models Beams with corroded reinforcing bars exposed to bending …”

Section: Introductionmentioning

confidence: 99%

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

Sýkora

Krejsa

Mlčoch

et al. 2018

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

“…In case the failure mode of the structure is more brittle, a different probabilistic model of the resistance model uncertainty is recommended. 18,19 The probabilistic model of the traffic load Q is selected to reflect a 50-year reference period, thus the reliability index is to be compared with β target of 3.8. For the sake of a meaningful comparison between the semi-probabilistic and reliability-based methods, the mean value of the traffic load Q 50 is set such that the reliability index is 3.8.…”

Section: Reliability Analysismentioning

confidence: 99%

On the value of a reliability‐based nonlinear finite element analysis approach in the assessment of concrete structures

Slobbe

Rózsás

Allaix

et al. 2019

The objective of this paper is to explore the value of reliability‐based nonlinear finite element analysis (NLFEA) over the currently available, standardized assessment methods. To our knowledge, no studies are available on this subject, and this paper provides a first insight into the value and reliability level of these assessment methods. The exploration is illustrated through three reinforced concrete structural members: a continuous girder, a continuous deep beam, and a high‐strength deep beam. The analysis is performed gradually: step by step advancing the approximation level of the mechanical and the probabilistic models. The added value of the reliability‐based NLFEA over the semi‐probabilistic Eurocode (EC) method is found to be on average 0.60. In other words: even if according to the semi‐probabilistic EC method the design action (Ed) is 60% higher than the design resistance (Rd), the compliance with the target reliability criterion can be demonstrated by a reliability‐based NLFEA. Furthermore, it is observed that the gain and its cause (i.e., more advanced mechanical or probabilistic models) are different for the three cases. Though this outcome is restricted to the analyzed cases and should be interpreted as an upper limit added value, it indicates that a more detailed physical representation of the problem and an explicit treatment of uncertainties may uncover substantial reserves compared with the currently available, standardized assessment methods. Hence, the reliability‐based NLFEA method offers a promising alternative in the assessment of existing structures, enabling to avoid expensive measures that might be needed based on simplified methods.