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A. Roy

5 records found

Authored

Efficient reliability analysis of concrete structures on the basis of non-linear finite element analysis under numerical noise

Doctoral thesis (2019) - A. Roy

The analytical expressions for the ultimate load bearing capacity of the RC structures do not provide the generalized notion of ultimate load bearing capacity, which can be obtained through nonlinear finite element analysis (NLFEA). In order to obtain an accurate estimate of failure probability of a RC structure it is necessary to use NLFEA based limit state function in a reliability analysis. However, there is a relative lack of NLFEA based reliability analysis efforts in the literature. Whatever efforts there are, none of them explicitly attempts to account for the uncertainty introduced by the NLFEA model, called modeling uncertainty, in the reliability analysis. Nor has there been much effort to study the impact of the numerical noise from NLFEA on the accuracy and efficiency of the reliability algorithms. Since the run time of each NLFEA is high, for a NLFEA based reliability analysis to be practically feasible it is imperative that the reliability algorithm is efficient and capable of handling different kinds of limit state functions (with multiple failure modes, for example). Keeping this in mind two adaptive response surface based methods, directional adaptive response surface method (DARS) and adaptive Kriging Monte Carlo simulation (AK-MCS), are selected based on the preliminary literature survey, for the investigation of NLFEA based reliability analysis of RC structures. The key objective of this thesis is to study the strengths and limitations of these two algorithms for RC structures and make necessary modifications in the DARS algorithm to make it more suitable for the reliability analysis of RC structure. A NLFEA solution strategy is formulated for RC beams and the modeling uncertainty is quantified based on 53 experimental results. Three RC beams, are selected as demonstrative cases. One of these beams fails in shear, another in bending and the last one can switch in failure modes between shear and bending. Based on these three beams it is demonstrated in this thesis that there is pronounced numerical noise in the NLFEA predicted bearing capacity whenever the beams fail is shear failure mechanism. Whereas for the bending failure mechanism the NLFEA solution strategy produces a much more smooth capacity prediction. Clear indications are found to the effect that the shear failure mechanism is more sensitive to certain choices adopted in the NLFEA solution strategy. @en

3-D stochastic finite elements for thermal creep analysis of piping structures with spatial material inhomogeneities

Journal article (2017) - Y. Appalanaidu, A. Roy, S. Gupta

A stochastic finite element-based methodology is developed for creep damage assessment in pipings carrying high-temperature fluids. The material properties are assumed to be spatially randomly inhomogeneous and are modelled as 3-D non-Gaussian fields. A spectral-based approach ...

Safety assessment of existing reinforced concrete beams using probabilistic methods at different levels

Conference paper (2016) - A. Roy, S. Robuschi, M.A.N. Hendriks, M.A.N. Hendriks, Beatrice Belletti

Several reliability methods available in literature combined with various modelling approaches are compared in this current work in the context of two experimental reinforced concrete (RC) beams. One beam failed in bending while the other beam failed in shear due to diagonal tens ...

Reliability analysis of reinforced concrete components

A comparative study

Conference paper (2016) - P. Evangeliou, A. Roy, M.A.N. Hendriks, R Steenbergen, A de Boer

Full probabilistic assessment of the structural reliability of reinforced concrete structures holds the key to proper calibration of the existing safety formats. The scope of the present work is to compare different level II reliability methods that take into account variability ...

Contributed

Reliability assessment of ‘simple’ statically indeterminate structures

Master thesis (2018) - J. de Jong, M.A.N. Hendriks, J.G. Rots, RDJM Steenbergen, A. Roy, Y. Yang, P. Evangeliou

Probability calculations are used to determine the possible failure of civil structures which includes bridges. The Eurocode uses a conservative form of these probability calculations and this could have a negative economic impact. Having said this, more advanced probability calculation methods are developed to decrease the negative economic impact this could have.
Nowadays structural analysis in daily practise is mostly done through the finite element method. The finite element method uses either linear or non-linear structural analysis. The latter mentioned analysis is used for the analysis of materials in which the nonlinear effects have significant impact. However not only finite element analyses are used to determine structural behaviour. Analytical models remain an important tool to examine civil structures. Since the analytical models cannot address all the influences of the nonlinear parameters, conservative assumptions were made.
On the one hand the modern design code uses semi-probabilistic in combination with the analytical model. Finite element analysis together with semi-probabilistic assessment is a possible use for design purposes as well. On the other hand full-probabilistic assessments, are not possible to execute in combination with nonlinear, finite element analyses. The reason for that the computation time becomes too large.
The research question that is tried to answer in this thesis: “How does a semi-probabilistic compare to a full-probabilistic safety assessment for a statically indeterminate beam structure?”
The 2-span statically indeterminate reinforced concrete beams that are studied in this thesis find their origin from the research done by Monnier between 1965 and 1970. This research had as goal to see what the influence of shear force would be on the bending capacity. This specific research is chosen because here statically indeterminate beams are dealt with. The experiments’ data generated during the execution of the four-point bending test is the starting point of this thesis.
To answer the research question, the components of a reliability model have been investigated. The levels of model approximation (LoA) as stated in the model code 2010 together with the level of reliability calculations (Steenbergen 2011) were used. Two combinations between LoA and reliability methods have been analysed to assess their strengths and weaknesses. These two reliability analyses were both were based on an analytical model (LoA I). The reliability level I and III, the so called semi-probabilistic and full-probabilistic, calculations were used.
In conclusion, the full-probabilistic reliability calculation is all cases applicable to determine the probability of failure of a statically indeterminate structure. However, semi-probability reliability are useful as well but it does allow only partly redistribution of forces. In case of statically indeterminate structures this can have significant impact on the failure load. The best reliability method for a statically indeterminate structure is dependent on the amount of redistribution of forces.
The semi-probabilistic calculations treat structures, where a lot of redistribution can occur, conservatively. For instance, the semi-probabilistic calculation procedure that is used in this thesis allows for only partly redistribution of forces. The full-probabilistic calculation procedure is therefore beneficial to use for structures where a lot of redistribution can occur in the ultimate limit state.
It turned out that the full-probabilistic calculation determines a higher reliability of the structure. In the full-probabilistic analysis, the limit state function is used in its analytical form. Whereas in the semi-probabilistic analysis is made with the use of approximations of the limit state function. However, when the cross-section of a statically indeterminate structure is designed in such a way that little redistribution will take place, the difference between the full- and semi-probabilistic is insignificant.