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See detailRole of interfacial transition zone in phase field modeling of fracture in layered heterogeneous structures
Nguyen, Thanh Tung UL; Waldmann, Danièle UL; Bui, T. Q.

in Journal of Computational Physics (2019), 386

Mechanical behavior of layered materials and structures greatly depends on the mechanical behavior of interfaces. In the past decades, the failure in such layered media has been studied by many ... [more ▼]

Mechanical behavior of layered materials and structures greatly depends on the mechanical behavior of interfaces. In the past decades, the failure in such layered media has been studied by many researchers due to their critical role in the mechanics and physics of solids. This study aims at investigating crack-interface interaction in two-dimensional (2-D) and three-dimensional (3-D) layered media by a phase field model. Our objectives are fourfold: (a) to better understand fracture behavior in layered heterogeneous systems under quasi-static load; (b) to introduce a new methodology for better describing interfaces by a regularized interfacial transition zone in the context of varia-tional phase field approach, exploring its important role; (c) to show the accuracy , performance and applicability of the present model in modeling material failure at the interfaces in both 2-D and 3-D bodies; and (d) to quantitatively validate computed crack path with respect to experimental data. Phase field models with both perfectly and cohesive bonded interfaces are thus derived. A regularized interfacial transition zone is introduced to capture characteristics of material mismatch at the interfaces. Numerical examples for 2-D and 3-D layered systems with experimental validation provide fundamentals of fracture behavior in layered structures. The obtained results shed light on the behavior of crack paths, which are drastically affected by the elastic modulus mismatch between two layers and interface types, and reveal the important role of the proposed interfacial transition zone in phase field modeling of crack interface interactions. [less ▲]

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See detailPhase field modeling of interfacial damage in heterogeneous media with stiff and soft interphases
Nguyen, Thanh Tung UL; Yvonnet, Julien; Waldmann, Danièle UL et al

in Engineering Fracture Mechanics (2019), 218

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See detailPhase field modeling of interfacial crack propagation in quasi-brittle heterogeneous materials
Nguyen, Thanh Tung UL; Yvonnet, Julien; Waldmann, Danièle UL et al

in International Conference on Computational Modeling of Fracture and Failure of Materials and Structures (2019)

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See detailBehaviour of Circular Fiber-Reinforced Polymer-Steel-Confined Concrete Columns Subjected to Reversed Cyclic Loads: Experimental Studies and FE Analysis
Wang, Yanlei; Cai, Gaochuang; Waldmann, Danièle UL et al

in Journal of Structural Engineering (2019)

This paper studies experimentally the behaviour of circular FRP-steel-confined columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behaviour of the columns ... [more ▼]

This paper studies experimentally the behaviour of circular FRP-steel-confined columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behaviour of the columns is discussed. Test results show the outstanding seismic performance of FRP-steel confined reinforced concrete (RC) and steel-reinforced concrete (SRC) column. The lateral confinement effectiveness of FRP materials is verified in the steel tube confined RC columns. A simplified finite element method (FEM) model supported by OpenSees is developed to simulate the experimental results of the test columns. Based on the proposed FEM model, a parametric analysis is conducted for investigating the effects of several main factors on the reversed cyclic behaviour of GFRP-steel confined RC columns. Based on the test and numerical analyses, the study discusses the influence of variables such as the lateral confinement on the plastic hinge region and peak drift ratio of the studied concrete columns under reversed cyclic loads. Results indicate that the lateral confinement significantly affects the height of plastic hinge region of circular confined columns without H-steel. Based on the analysies of test data from the study and literature, the paper suggests a simple model to predict the peak drift ratio of the confined RC columns. [less ▲]

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See detailStatic load deflection experiment on a beam for damage detection using the Deformation Area Difference Method
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Teferle, Felix Norman UL

Scientific Conference (2018, October)

A reliable and safety infrastructure for both transport and traffic is becoming increasingly important today. The condition assessment of bridges remains difficult and new methods must be found to provide ... [more ▼]

A reliable and safety infrastructure for both transport and traffic is becoming increasingly important today. The condition assessment of bridges remains difficult and new methods must be found to provide reliable information. A meaningful in-situ assessment of bridges requires very detailed investigations which cannot be guaranteed by commonly used methods. It is known that the structural response to external loading is influenced by local damages. However, the detection of local damage depends on many factors such as environmental effects (e.g. temperature), construction layer (e.g. asphalt) and accuracy of the structural response measurement. Within the paper, a new so-called Deformation Area Difference (DAD) Method is presented. The DAD method is based on a load deflection experiment and does not require a reference measurement of initial condition. Therefore, the DAD method can be applied on existing bridges. Moreover, the DAD method uses the most modern technologies such as high precision measurement techniques and attempts to combine digital photogrammetry with drone applications. The DAD method uses information given in the curvature course from a theoretical model of the structure and compares it to real measurements. The paper shows results from a laboratory load-deflection experiment with a steel beam which has been gradually damaged at distinct positions. The load size is chosen so that the maximum deflection does not exceed the serviceability limit state. With the data obtained by the laboratory experiment, the damage degree, which can still be detected by the DAD method, is described. Furthermore, the influence of measurement accuracy on damage detection is discussed. [less ▲]

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See detailAssessment of the suitability of gravel wash mud as raw material for the synthesis of an alkali-activated binder
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Wagner, Jean-Frank et al

in Applied Clay Science (TOP10 Journal in Mineralogy) (2018), 161(C), 110-118

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of ... [more ▼]

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of an alkali-activated binder. The GWM powders were thermally treated at five different calcination temperatures 550, 650, 750, 850 and 950°C. The characterisation of the raw material comprises the particle size distribution (PSD) by laser granulometry, the chemical and mineralogical composition by X-ray fluorescence and X-ray diffraction analysis respectively, and simultaneous thermal analysis. The performance of the alkali-activated binders was examined using compression strength tests and the microstructure was observed using scanning electron microscopy (SEM). The GWM was classified as an aluminosilicate raw material with kaolinite and illite as main clay minerals. Furthermore, a mean particle size around 6.50μm was determined for the uncalcined and calcined GWM powders. The SEM images of the developed binders showed the formation of a compact microstructure, however, relatively low strengths were achieved. This preliminary study highlights an example of an aluminosilicate prime material, which shows very promising chemical and mineralogical characteristics, but its suitability for alkaline activation without further additives was not confirmed as far as performance-based criteria are considered. [less ▲]

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See detailBloc pour construction seche
Waldmann, Danièle UL; Chewe Ngapeya, Gelen Gael UL; Spina, Carlo et al

Patent (2018)

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See detailImpact of the height imperfections of masonry blocks on the load bearing capacity of dry-stack masonry walls
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL; Scholzen, Frank UL

in Journal of Construction and Building Materials (TOP10 journal) (2018), 165

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the ... [more ▼]

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the structural response and the load bearing capacity of masonry walls by highlighting the load percolation. Furthermore, an algorithm was developed to define a stress multiplier coefficient respecting the imperfections ΔH. The algorithm allowed predicting 77% of the amplified stress compared to the FE analysis and showed that the geometric imperfections govern the load percolation in a wall as well as the cracking mode and the bearing capacity. [less ▲]

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See detailA short review on alkali-activated binders and geopolymer binders
Waldmann, Danièle UL; Thapa, Vishojit Bahadur UL

in Pahn, Matthias; Thiele, Catherina; Glock, Christian (Eds.) Vielfalt im Massivbau - Festschrift zum 65. Geburtstag von Prof. Dr. Ing. Jürgen Schnell (2018)

In the recent years, the trend for reusing waste products or industrial by-products to reduce the amount of Ordinary Portland Cement (OPC) in concrete constructions has become an important task for ... [more ▼]

In the recent years, the trend for reusing waste products or industrial by-products to reduce the amount of Ordinary Portland Cement (OPC) in concrete constructions has become an important task for industries and research institutions. OPC is the second most used material in the world after water and statistics confirm that the life cycle of OPC contributes to the generation of up to 5% of the annual CO2 emissions worldwide. Mostly responsible for this negative environmental performance of OPC are the high CO2 emissions related to the cement production processes, namely the deacidification of limestone and the burning of the clinker raw materials at high temperatures above 1400°C. The current demand for cementitious binder is higher than ever whereas the incentive of building sustainable and robust constructions is gaining increasingly in importance. There is a need for development of new more durable and environmental friendly binders as an alternative to OPC binders. Therefore, the research on cement alternatives has risen over the last decades and a lot of research work has been carried out to fulfil the requirements of the market. In this work, the concepts of alkali activated materials and geopolymers are presented, and their properties are compared and discussed. A short historical review is given. Furthermore, the reaction mechanisms and hydration products of these binders are characterized and explained by referring to literature. Finally, novel binders based on waste materials are presented before closing with a short outlook on remaining questions and future challenges. [less ▲]

Detailed reference viewed: 248 (18 UL)
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See detailThe Deformation Area Difference (DAD) method for condition assessment of reinforced structures
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Scherbaum, Frank et al

in Engineering Structures (2018), 155

The investigation and condition assessment of bridges have a very high priority in the construction industry today. Particularly, due to the fact that many bridge structures are getting old and partly ... [more ▼]

The investigation and condition assessment of bridges have a very high priority in the construction industry today. Particularly, due to the fact that many bridge structures are getting old and partly reach the end of their useful life, the control and condition assessment of bridge structures have become very important and essential. The present research work introduces an efficient new method for condition assessment called the Deformation Area Difference (DAD) Method. This new method represents an attractive alternative to visual inspection and long-term monitoring. In this paper, the new method with its theoretical background is presented and explained by means of a laboratory experiment and some additional theoretical calculation examples. The experimental investigations have been realised on a reinforced concrete beam, which has been gradually loaded until failure. For each load step, the stiffness reduction and the apparent cracking have been monitored. High-precision measurements such as close-range photogrammetry, digital levelling and displacement sensors have been used for the determination of the deflection curve. The DAD method has been applied to identify the area of the crack pattern of the laboratory experiment. Furthermore, the method is discussed with regard to the load level and the precision of the deformation measurements. On the basis of the laboratory experiment, the applicability of the DAD method for damage detection could be proven. Furthermore, the sensitivity of the method with regard to the damage degree, the static system, the damage position and the impact of temperature variation were analysed. [less ▲]

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See detailAnalysis of a masonry block based on lightweight Miscanthus concrete
Pereira Dias, Patrick UL; Waldmann, Danièle UL

in Revue Technique Luxembourgeoise (2018)

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See detailRender comprising honeycomb and cementitious or clay or geopolymer material
Waldmann, Danièle UL; Gilbert de Cauwer, Jacques

Patent (2018)

Detailed reference viewed: 85 (15 UL)
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See detailModelling of early-age complex crack propagation in cement-based materials using phase field method
Nguyen, Thanh Tung UL; Waldmann, Danièle UL

in 6th European Conference on Computational Mechanics (2018)

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See detailPhase field simulation of early-age fracture in cement-based materials
Nguyen, Thanh Tung UL; Waldmann, Danièle UL; Bui, T. Q.

E-print/Working paper (2018)

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See detailA new thickness-based accelerated aging test methodology for resin materials: theory and preliminary experimental study
Wang, Yanlei; Zhang, Xue; Gaochuang, Cai et al

in Construction and Building Materials (2018)

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See detailLaboratory experiment for damage assessment using the DAD-method
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Teferle, Felix Norman UL

in Conference proceedings SMAR 2017 (2017, September)

In the following, a new analytical method, the Deformation Area Difference (DAD) method for damage assessment of bridge structures is applied using experimental test results of a statically loaded beam ... [more ▼]

In the following, a new analytical method, the Deformation Area Difference (DAD) method for damage assessment of bridge structures is applied using experimental test results of a statically loaded beam. An essential prerequisite for the application of this method is a high precise measurement of the deflection line. In this paper, the results from a laboratory experiment using modern measurement techniques such as photogrammetry and displacement sensors are discussed. A reinforced concrete beam is stepwise loaded until reaching the ultimate limit state. The DAD-method is applied to the resulting data from the measurements and the outcome is discussed for further optimisation of the method. In principle, the measured deflection line of the beam contains already essential information on discontinuities which occur due to cracking. These entries are processed and visualised using the DAD-method. This study shows that a high accuracy of the measurement techniques in combination with the DAD-method can become an effective tool for damage detection. [less ▲]

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See detailDemountable construction enables structural diversity
Waldmann, Danièle UL

in Adjacent open access (2017)

Detailed reference viewed: 79 (20 UL)