A. Dimmig-osburg - Academia.edu (original) (raw)
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Papers by A. Dimmig-osburg
Tests on Polymer Modified Cement Concrete (PCC) have shown significant large creep deformation. T... more Tests on Polymer Modified Cement Concrete (PCC) have shown significant large creep deformation. The reason for that as well as additional material phenomena are explained in the following paper. Existing creep models developed for standard concrete are studied to determine the time-dependent deformations of PCC. These models are: model B3 by Bazant and Bajewa, the models according to Model Code
Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures, 2014
ABSTRACT With the increasing use of reinforced concrete for bridges, offshore structures, it is n... more ABSTRACT With the increasing use of reinforced concrete for bridges, offshore structures, it is necessary to know the serviceability behaviour in additional to the ultimate behaviour of structures subjects to cyclic and fatigue loading. Modeling cyclic creep of concrete has been one of the most challenging problems in concrete. This paper presents a methodology for Uncertainty Quantification (UQ) in cyclic creep deflection. Several models: mathematical creep model, finite element model are analysed. Three types of uncertainty are included in UQ: (i) natural variability in loading, materials and environmental properties; (ii) data uncertainty due to measurement errors (metrological aspects); and (iii) modelling uncertainty and errors during cyclic creep deflection analysis, numerical approximation, and finite element discretization. All input imperfections were considered to be random quantities. This research investigation is divided into: first an in depth study of the cyclic creep data and development of a homogeneous dataset that can be used for computational analysis. Second: developing probabilistic Monte Carlo methods that enable uncertainty and identifying the important parameters that affecting the cyclic creep of concrete. Although the uncertainty inherent in measured data used to calibrate and validate model predictions is commonly acknowledge, measurement uncertainty is rarely included in the evaluation of structural behavior. On reason for this omission is the lack of data on the uncertainty based on a statistical analysis of observations and the uncertainty derived from metrological aspects. Measurement uncertainties are utilized for the derivation of a methodology for the uncertainty propagation through simulation model. This facilitates the quantification of a measurement uncertainty using all available data of the measurement cyclic creep deflection process. Third discusses the problem of quantifying the contribution of random and systematic errors on the overall measurement uncertainty. The proposed methodology is illustrated using a numerical example of cyclic creep deflection in a simply supported concrete beam.
2nd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR-2, 24-26 November 2008, Cape Town, South Africa, 2008
For PCC as a constructional material two parameters are of particular importance: the deformation... more For PCC as a constructional material two parameters are of particular importance: the deformation behaviour and the stiffness evolution at mechanical loading. The microstructure and the composition are the main differences between normal concrete and polymer modified concrete. To understand the deformation behaviour of PCC it is necessary to survey the behaviour of the polymer matrix under mechanical load. There are two ways how concrete is influenced by polymers under mechanical load. Firstly, strong polymer films demand a higher load to open the micro-crack edges so that the tensile strength increases. Secondly, a small particle size raises the specific adhesion between the matrix and the sand grains, which also leads to an increasing tensile strength. In fact, it is a co-action of both ways, depending on the kind of polymers, their particle sizes, their film tensile strengths, and their film formation temperatures.
Restoration of Buildings and Monuments, 2008
For PCC as a constructional material two parameters are of particular importance: the deformation... more For PCC as a constructional material two parameters are of particular importance: the deformation behaviour and the stiffness evolution at mechanical loading. The microstructure and the composition are the main differences between normal concrete and polymer modified concrete. To understand the deformation behaviour of PCC it is necessary to survey the behaviour of the polymer matrix under mechanical load. There are two ways how concrete is influenced by polymers under mechanical load. Firstly, strong polymer films demand a higher load to open the micro-crack edges so that the tensile strength increases. Secondly, a small particle size raises the specific adhesion between the matrix and the sand grains, which also leads to an increasing tensile strength. In fact, it is a co-action of both ways, depending on the kind of polymers, their particle sizes, their film tensile strengths, and their film formation temperatures.
In civil engineering experimental models are used for the parameter identification, validation/ve... more In civil engineering experimental models are used for the parameter identification, validation/verification of numerical models and study of the behaviour of reality. All these activities are strongly connected with the development of experimental activity,
where measurement has a fundamental role. Experimental models are usually support the development of mathematical models and provide measurement results with acceptable
quality.
This paper presents a methodology for the quality evaluation of experimental results. It also suggests a generalization of standard approaches for characterizing experimental uncertainty that carefully distinguishes and retains separate different forms of uncertainty. In particular, the probabilistic approach can provide significant information during the
evaluation process. Therefore, methods for predicting the uncertainty, sensitivity, and reliability are proposed for quality evaluation of experimental results. Furthermore, different
uncertainties are to be taken into consideration when comparing different experimental
models with different level of complexity. For this purpose, different approaches for predicting these uncertainties are implemented. Their contribution to the reliability of
materials testing are illustrated. From this study it can be concluded that the presented
methodology provides mathematical and computational tool and is able to quantify the model uncertainty. Moreover, it is useful to improve measurement processes to promote
quality and capacity with decision-making.
Engineering Science and Technology, an International Journal, 2014
Strain measurement is important in mechanical testing. A wide variety of techniques exists for me... more Strain measurement is important in mechanical testing. A wide variety of techniques exists for measuring strain in the tensile test; namely the strain gauge, extensometer, stress and strain determined by machine crosshead motion, Geometric Moire technique, optical strain measurement techniques and others. Each technique has its own advantages and disadvantages. The purpose of this study is to quantitatively compare the strain measurement techniques. To carry out the tensile test experiments for S 235, sixty samples were cut from the web of the I-profile in longitudinal and transverse directions in four different dimensions. The geometry of samples are analysed by 3D scanner and vernier caliper. In addition, the strain values were determined by using strain gauge, extensometer and machine crosshead motion. Three techniques of strain measurement are compared in quantitative manner based on the calculation of mechanical properties (modulus of elasticity, yield strength, tensile strength, percentage elongation at maximum force) of structural steel. A statistical information was used for evaluating the results. It is seen that the extensometer and strain gauge provided reliable data, however the extensometer offers several advantages over the strain gauge and crosshead motion for testing structural steel in tension. Furthermore, estimation of measurement uncertainty is presented for the basic material parameters extracted through strain measurement.
The intention of this paper is to evaluate the uncertainties and sensitivities of creep predictio... more The intention of this paper is to evaluate the uncertainties and sensitivities of creep prediction models of standard concrete. The development of creep prediction models has been a field of extensive research and many different models have already been proposed. The four major models are: model GL2000 by Gardner and Lockman, model MC90 according to CEB-FIP Model Code 1990, model
Materials and Structures, 2012
ABSTRACT The development of creep prediction models has been a field of extensive research and ma... more ABSTRACT The development of creep prediction models has been a field of extensive research and many different models have already been proposed. This paper presents an evaluation method of the prediction quality of creep models for specific experimental data. Within the scope of this paper, the model according to Bockhold and the model according to Heidolf are examined. First, the parameters of the models are identified with respect to existing experimental data. This is done using a sampling based approach of Bayesian updating developed by Bažant and Chern. In extension to the method by Bažant and Chern, the uncertainty coming from inaccurate measurement data is taken into account in the definition of the likelihood function within the updating algorithm. The more inaccurate the measurements are, the more uncertain the estimated model parameters and model prognoses become. The identification is performed for different short- and long-term creep tests. The intension is not to validate these models intensively, but to evaluate their prognoses for the individually tested creep behavior. The results show that the identifiability of the models’ parameters is different for both models and consequently the models prognoses differ in their uncertainties. Second, the models are evaluated using two different strategies: the stochastic model selection according to MacKay, Beck and Yuen based on the Ockham factor, and a comparison of the uncertainties taking into account parameter and model uncertainties. The results of the evaluation of the creep models differ for various experimental tests. Model Heidolf is more flexible and gives a better fit to the data, however, it fails to predict reliable long-term creep deformations using only short-term measurements compared to model Bockhold. Comparing the evaluation methods, the analysis of uncertainties of the creep prognosis proofs to be more stable than the evaluation using the stochastic model selection.
Tests on Polymer Modified Cement Concrete (PCC) have shown significant large creep deformation. T... more Tests on Polymer Modified Cement Concrete (PCC) have shown significant large creep deformation. The reason for that as well as additional material phenomena are explained in the following paper. Existing creep models developed for standard concrete are studied to determine the time-dependent deformations of PCC. These models are: model B3 by Bazant and Bajewa, the models according to Model Code
Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures, 2014
ABSTRACT With the increasing use of reinforced concrete for bridges, offshore structures, it is n... more ABSTRACT With the increasing use of reinforced concrete for bridges, offshore structures, it is necessary to know the serviceability behaviour in additional to the ultimate behaviour of structures subjects to cyclic and fatigue loading. Modeling cyclic creep of concrete has been one of the most challenging problems in concrete. This paper presents a methodology for Uncertainty Quantification (UQ) in cyclic creep deflection. Several models: mathematical creep model, finite element model are analysed. Three types of uncertainty are included in UQ: (i) natural variability in loading, materials and environmental properties; (ii) data uncertainty due to measurement errors (metrological aspects); and (iii) modelling uncertainty and errors during cyclic creep deflection analysis, numerical approximation, and finite element discretization. All input imperfections were considered to be random quantities. This research investigation is divided into: first an in depth study of the cyclic creep data and development of a homogeneous dataset that can be used for computational analysis. Second: developing probabilistic Monte Carlo methods that enable uncertainty and identifying the important parameters that affecting the cyclic creep of concrete. Although the uncertainty inherent in measured data used to calibrate and validate model predictions is commonly acknowledge, measurement uncertainty is rarely included in the evaluation of structural behavior. On reason for this omission is the lack of data on the uncertainty based on a statistical analysis of observations and the uncertainty derived from metrological aspects. Measurement uncertainties are utilized for the derivation of a methodology for the uncertainty propagation through simulation model. This facilitates the quantification of a measurement uncertainty using all available data of the measurement cyclic creep deflection process. Third discusses the problem of quantifying the contribution of random and systematic errors on the overall measurement uncertainty. The proposed methodology is illustrated using a numerical example of cyclic creep deflection in a simply supported concrete beam.
2nd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR-2, 24-26 November 2008, Cape Town, South Africa, 2008
For PCC as a constructional material two parameters are of particular importance: the deformation... more For PCC as a constructional material two parameters are of particular importance: the deformation behaviour and the stiffness evolution at mechanical loading. The microstructure and the composition are the main differences between normal concrete and polymer modified concrete. To understand the deformation behaviour of PCC it is necessary to survey the behaviour of the polymer matrix under mechanical load. There are two ways how concrete is influenced by polymers under mechanical load. Firstly, strong polymer films demand a higher load to open the micro-crack edges so that the tensile strength increases. Secondly, a small particle size raises the specific adhesion between the matrix and the sand grains, which also leads to an increasing tensile strength. In fact, it is a co-action of both ways, depending on the kind of polymers, their particle sizes, their film tensile strengths, and their film formation temperatures.
Restoration of Buildings and Monuments, 2008
For PCC as a constructional material two parameters are of particular importance: the deformation... more For PCC as a constructional material two parameters are of particular importance: the deformation behaviour and the stiffness evolution at mechanical loading. The microstructure and the composition are the main differences between normal concrete and polymer modified concrete. To understand the deformation behaviour of PCC it is necessary to survey the behaviour of the polymer matrix under mechanical load. There are two ways how concrete is influenced by polymers under mechanical load. Firstly, strong polymer films demand a higher load to open the micro-crack edges so that the tensile strength increases. Secondly, a small particle size raises the specific adhesion between the matrix and the sand grains, which also leads to an increasing tensile strength. In fact, it is a co-action of both ways, depending on the kind of polymers, their particle sizes, their film tensile strengths, and their film formation temperatures.
In civil engineering experimental models are used for the parameter identification, validation/ve... more In civil engineering experimental models are used for the parameter identification, validation/verification of numerical models and study of the behaviour of reality. All these activities are strongly connected with the development of experimental activity,
where measurement has a fundamental role. Experimental models are usually support the development of mathematical models and provide measurement results with acceptable
quality.
This paper presents a methodology for the quality evaluation of experimental results. It also suggests a generalization of standard approaches for characterizing experimental uncertainty that carefully distinguishes and retains separate different forms of uncertainty. In particular, the probabilistic approach can provide significant information during the
evaluation process. Therefore, methods for predicting the uncertainty, sensitivity, and reliability are proposed for quality evaluation of experimental results. Furthermore, different
uncertainties are to be taken into consideration when comparing different experimental
models with different level of complexity. For this purpose, different approaches for predicting these uncertainties are implemented. Their contribution to the reliability of
materials testing are illustrated. From this study it can be concluded that the presented
methodology provides mathematical and computational tool and is able to quantify the model uncertainty. Moreover, it is useful to improve measurement processes to promote
quality and capacity with decision-making.
Engineering Science and Technology, an International Journal, 2014
Strain measurement is important in mechanical testing. A wide variety of techniques exists for me... more Strain measurement is important in mechanical testing. A wide variety of techniques exists for measuring strain in the tensile test; namely the strain gauge, extensometer, stress and strain determined by machine crosshead motion, Geometric Moire technique, optical strain measurement techniques and others. Each technique has its own advantages and disadvantages. The purpose of this study is to quantitatively compare the strain measurement techniques. To carry out the tensile test experiments for S 235, sixty samples were cut from the web of the I-profile in longitudinal and transverse directions in four different dimensions. The geometry of samples are analysed by 3D scanner and vernier caliper. In addition, the strain values were determined by using strain gauge, extensometer and machine crosshead motion. Three techniques of strain measurement are compared in quantitative manner based on the calculation of mechanical properties (modulus of elasticity, yield strength, tensile strength, percentage elongation at maximum force) of structural steel. A statistical information was used for evaluating the results. It is seen that the extensometer and strain gauge provided reliable data, however the extensometer offers several advantages over the strain gauge and crosshead motion for testing structural steel in tension. Furthermore, estimation of measurement uncertainty is presented for the basic material parameters extracted through strain measurement.
The intention of this paper is to evaluate the uncertainties and sensitivities of creep predictio... more The intention of this paper is to evaluate the uncertainties and sensitivities of creep prediction models of standard concrete. The development of creep prediction models has been a field of extensive research and many different models have already been proposed. The four major models are: model GL2000 by Gardner and Lockman, model MC90 according to CEB-FIP Model Code 1990, model
Materials and Structures, 2012
ABSTRACT The development of creep prediction models has been a field of extensive research and ma... more ABSTRACT The development of creep prediction models has been a field of extensive research and many different models have already been proposed. This paper presents an evaluation method of the prediction quality of creep models for specific experimental data. Within the scope of this paper, the model according to Bockhold and the model according to Heidolf are examined. First, the parameters of the models are identified with respect to existing experimental data. This is done using a sampling based approach of Bayesian updating developed by Bažant and Chern. In extension to the method by Bažant and Chern, the uncertainty coming from inaccurate measurement data is taken into account in the definition of the likelihood function within the updating algorithm. The more inaccurate the measurements are, the more uncertain the estimated model parameters and model prognoses become. The identification is performed for different short- and long-term creep tests. The intension is not to validate these models intensively, but to evaluate their prognoses for the individually tested creep behavior. The results show that the identifiability of the models’ parameters is different for both models and consequently the models prognoses differ in their uncertainties. Second, the models are evaluated using two different strategies: the stochastic model selection according to MacKay, Beck and Yuen based on the Ockham factor, and a comparison of the uncertainties taking into account parameter and model uncertainties. The results of the evaluation of the creep models differ for various experimental tests. Model Heidolf is more flexible and gives a better fit to the data, however, it fails to predict reliable long-term creep deformations using only short-term measurements compared to model Bockhold. Comparing the evaluation methods, the analysis of uncertainties of the creep prognosis proofs to be more stable than the evaluation using the stochastic model selection.