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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 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 in press ELSEVIER Construction and Building Materials (TOP10 journal) (2018)

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 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 detailInfluence of the sheet profile design on the composite action of slabs made of lightweight woodchip concrete
Waldmann, Danièle UL; May, Andreas; Thapa, Vishojit Bahadur UL

in ELSEVIER Construction & Building Materials (2017), 148C(September 2017), 887-899

The trend for using renewable materials in construction to create sustainable and robust buildings is currently gaining in popularity. Therefore, in this work, the applicability of dense lightweight ... [more ▼]

The trend for using renewable materials in construction to create sustainable and robust buildings is currently gaining in popularity. Therefore, in this work, the applicability of dense lightweight woodchip concrete in constructive engineering is investigated. Here, the material is used as a top concrete layer on composite floors with profiled sheets and is analysed with regard to its load-bearing behaviour and composite action. One specific concrete mixture which fulfils the requirement for minimum strength of LC 20/22 is used for the test series. The scale of the study comprises 22 plate elements in total. The varied parameters are the shear spans, profiled sheet types and sheet thicknesses. Each examined sheet has an undercut profile with additional embossment. On the basis of experimental results, the influences of the varied parameters and profile forms on the load-bearing and composite behaviour are discussed. This study provides important key findings which show that dense lightweight woodchip concrete can transfer sufficient longitudinal shear forces to the composite joint. [less ▲]

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See detailDemountable construction enables structural diversity
Waldmann, Danièle UL

in Adjacent open access (2017)

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See detailMechanical characterisation of alkali activated clay - based geopolymer binder made out of gravel wash mud
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Wagner, Jean-Frank et al

Poster (2017, April 03)

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits and classifies all forms of inorganic polymeric material ... [more ▼]

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits and classifies all forms of inorganic polymeric material synthesised by chemical reaction of aluminosilicates and an alkaline activating solution. The production of geopolymer binder comprises in two main procedures: calcination and geopolymerisation. The synthesised geopolymer shows interesting characteristics like good mechanical properties, high strength and good durability. [less ▲]

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See detailMechanical characterisation of alkali activated clay - based geopolymer binder made out of gravel wash mud
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Wagner, Jean-Frank et al

in Iacobescu, Remus Ion; Malfliet, Annelies (Eds.) Proceedings of the 5th International Slag Valorisation Symposium (2017, April)

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits1 and classifies all forms of inorganic polymeric material ... [more ▼]

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits1 and classifies all forms of inorganic polymeric material synthesised by chemical reaction of aluminosilicates and an alkaline activating solution. The production of geopolymer binder comprises in two main procedures: calcination and geopolymerisation. The synthesised geopolymer shows interesting characteristics like good mechanical properties, high strength and good durability. [less ▲]

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See detailHealth Monitoring based on Dynamic Flexibility matrix: Theoretical Models versus in-situ Tests
Schommer, Sebastian UL; Mahowald, Jean; Nguyen, Viet Ha UL et al

in Engineering (2017), 09(02), 37-67

The paper focuses on damage detection of civil engineering structures and especially on concrete bridges. A method for structural health monitoring based on vibrational measurements is presented and ... [more ▼]

The paper focuses on damage detection of civil engineering structures and especially on concrete bridges. A method for structural health monitoring based on vibrational measurements is presented and discussed. Experimentally identified modal parameters (eigenfrequencies, mode shapes and modal masses) of bridge structures are used to calculate the inverse stiffness matrix, the so-called flexibility matrix. By monitoring of the stiffness matrix, damage can easily be detected, quantified and localized by tracking changes of its individual elements. However, based on dynamic field measurements, the acquisition of the flexibility matrix instead of the stiffness matrix is often the only choice and hence more relevant for practice. But the flexibility-based quantification and localisation of damage are often possible but more difficult, as it depends on the type of support and the location of the damage. These issues are discussed and synthetized, that is an originality of this paper and is believed useful for engineers in the damage detection of different bridge structures. First the theoretical background is briefly repeated prior to the illustration of the differences between stiffness and flexibility matrix on analytical and numerical examples. Then the flexibility-based detection is demonstrated on two true bridges with real-time measurement data and the results are promising. [less ▲]

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See detailNumerical Analysis for the determination of Stress Percolation in Dry-Stacked Wall Systems
Agaajani, Shahriar; Waldmann, Danièle UL; Scholzen, Frank UL et al

in Masonry International (2016)

This paper comprises a portion of a PhD study concluding on the potential use of a new mortarless and modular masonry system by taking into consideration the outcome of a multidisciplinary study including ... [more ▼]

This paper comprises a portion of a PhD study concluding on the potential use of a new mortarless and modular masonry system by taking into consideration the outcome of a multidisciplinary study including aspects of experimental, numerical and analytical investigations in relation to a practical and economical development of modular load-bearing dry-stacked masonry systems. Different forms of interlocking masonry elements have been modelled and optimised thermo-mechanically. Full-scale masonry walls were assembled and tested experimentally under compressive, flexural, shear, cyclic and long term loads. The overall structural behaviour was compared to conventional masonry systems such as hollow and shuttering blocks. The investigations showed overall relative high structural performances for the developed dry-stacked elements. The effect of dry joint interfaces was extensively investigated experimentally and numerically under FE analysis. Based on the experimental observations, a numeric-analytical failure mechanism of the dry-stacked masonry structure is anticipated under axial and flexural loading. The structural investigations and engineering processes are completed by the development of a package of dry-stacked units consisting of interlocking modular masonries and an accompanying array of various other precast parts. This confirmed the practical issues and solutions towards the exploitation of the developed dry-stacked elements for the construction of ready-to-build, modular and load-bearing walls. The portion of work presented herein proposes a new numerical technique for the determination of stress-percolation in dry stacked load-bearing structures. The model is developed in three steps under a numerical computing environment. First, based on geometrical properties of the dry-stacked elements and with a linear-elastic material behaviour, the load percolation and intensity in dry-stacked masonry walls is determined. In a second step, a phenomenon known as a plastic accommodation which accompanies the redistribution of the stress percolations, is incorporated in the model. This enables the understanding of the evolution of the stress percolations in the post-elastic phase, which is crucial for the determination of the load capacity and stability of the structure in function of an increased external load. This paper also supports the better understanding of early fissuring in dry-stacked masonry structures which has an important influence on the overall stability of the structure. Finally, in a third step, the improvement of dry-stacked structures is pursued by further analysis of the results obtained through the algorithm. This paper represents a new tool for investigating the localized and randomly defined internal stress distribution induced by external compression forces on dry-stacked structures. Furthermore, the algorithm illustrates that experimental investigations on dry-stacked systems may only give real indications on the load capacity of the structure, when the number of joint interfaces and height to length ratio of the block is respected and that results of experimental investigations on reduced prism specimens may not be extrapolated to full sized walls as they may over-evaluate the effective loaded masonry sections and therefore the overall load capacity. [less ▲]

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See detailCondition assessment and damage localisation for bridges by use of the Deformation Area Difference Method (DAD-Method)
Erdenebat, Dolgion UL; Waldmann, Danièle UL

in Performance-based approaches for concrete structures (2016, November)

Already today, a huge number of bridges are in an ailing condition due to their increasing age and due to an increased traffic volume, especially of heavy transport vehicles. To assess their load bearing ... [more ▼]

Already today, a huge number of bridges are in an ailing condition due to their increasing age and due to an increased traffic volume, especially of heavy transport vehicles. To assess their load bearing capacity and subsequently predict their remaining life span, every bridge needs to be analysed by con-dition assessment. The consequences of unreliable condition assessment should not be underestimated, as most bridge constructions constitute cost intensive and indispensable infrastructures. Thus, modern condition assessment methods, easy and obvious in their application, are needed in order to reduce future investigations. To offer an easy handling alternative to evaluate the condition of bridges, the Deformation Area Dif-ference Method has been developed. Hereby, the accruing deformation of bridges under a static load will be analysed with the help of modern measurement equipment. Therefore, the resulting defor-mation curves like the deflection, the inclination angle and the curvature curves, will be analysed in one diagram together with the results out of initial measurements or theoretically calculated defor-mation curves. The DAD-Method is then applied on the surface difference area between those two curves for the deflection, the inclination and the curvature. It will be demonstrated that a localisation of damage is possible, independent from the degree of damage. In this study, the applicability of the DAD-Method including the comparison of innovative measure-ment techniques using a laboratory specimen is investigated. For further explanation of the back-ground of the DAD-Method, the results from a FE-calculation are presented. [less ▲]

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See detailConcept to predict crack initiation and crack development in fairfaced concrete screeds
Weiler, Michael UL; Waldmann, Danièle UL

in Beushausen, Hans (Ed.) Performance-based approaches for concrete structures (2016, November)

Within a research project of the Laboratory of Solid Structures of the University of Luxemburg, a design concept to predict cracks in various concrete structures will be developed. The current paper ... [more ▼]

Within a research project of the Laboratory of Solid Structures of the University of Luxemburg, a design concept to predict cracks in various concrete structures will be developed. The current paper presents the numerical investigation of crack initiation and crack development of an unreinforced cementitious fairfaced concrete floor. Thereby cracking of concrete is divided into cracking of an early stage and into cracking of a later stage. The present study deals with cracking of an early stage. Taking into account shrinkage and the chronological strength development of the used C20/25 concrete and with the use of the Element Failure Method (EFM) it will be possible to predict, within a Finite Element Analysis, a possible crack path spatial as well as temporal. For this purpose a finite element model, based on a commercial FE-Software is developed. The program is tested on H-shaped concrete specimen with an unfavorable size ratio between surface and volume. Besides, shrinkage on this specimen is hindered so that unplanned restrain forces has to occur. Using an algorithm the finite element program is able to calculate the model gradually for several load steps within a loop. Furthermore the net dependency of the EFM can be excluded by the use of suitable load steps. [less ▲]

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See detailNumerical investigation of bridges with the aim of condition assessment in applying the Deformation Area Difference method (DAD-method) and selecting appropriate measurement techniques
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Teferle, Felix Norman UL

in 5th International Symposium on Life-Cycle Civil Engineering (IALCCE 2016), Delft (2016, October)

Condition assessment of existing road bridges gains ever increasing importance today as bridges are getting older and the inflow of heavy traffic is constantly increasing. The further development of ... [more ▼]

Condition assessment of existing road bridges gains ever increasing importance today as bridges are getting older and the inflow of heavy traffic is constantly increasing. The further development of recognized techniques and the development of new methods for early and accurate detection of damage to the structure are made possible by means of innovative technological progress. In this contribution, the principles of Defor-mation Area Difference Method (DAD-Method) for condition assessment of bridges are presented. This method is based on the further processing of measured and computed deformation values. The application of the DAD-Method requires a precise recording of the deflection of a load-deflection test. On the basis of theoretical cal-culations, this method has allowed to identify as well as to localise damage to a structure. The DAD-Method is independent of a reference measurement and insensitive to global influences such as temperature fluctuations. For precise detection of deformations, the most modern measuring instruments and methods like photogram-metry, total stations, displacement sensors, strain gauges and levelling are compared to each other. In collabo-ration with the appropriate measurement technology, the localisation of damage in bridges becomes possible. [less ▲]

Detailed reference viewed: 150 (42 UL)
See detailNumerical Analysis for the determination of Stress Percolation in Dry-Stacked Wall Systems
Agaajani, Shahriar; Waldmann, Danièle UL; Scholzen, Frank UL et al

in Revue Technique (2016)

This paper comprises a portion of a PhD study concluding on the potential use of a new mortarless and modular masonry system by taking into consideration the outcome of a multidisciplinary study including ... [more ▼]

This paper comprises a portion of a PhD study concluding on the potential use of a new mortarless and modular masonry system by taking into consideration the outcome of a multidisciplinary study including aspects of experimental, numerical and analytical investigations in relation to a practical and economical development of modular load-bearing dry-stacked masonry systems. Different forms of interlocking masonry elements have been modelled and optimised thermo-mechanically. Full-scale masonry walls were assembled and tested experimentally under compressive, flexural, shear, cyclic and long term loads. The overall structural behaviour was compared to conventional masonry systems such as hollow and shuttering blocks. The investigations showed overall relative high structural performances for the developed dry-stacked elements. The effect of dry joint interfaces was extensively investigated experimentally and numerically under FE analysis. Based on the experimental observations, a numeric-analytical failure mechanism of the dry-stacked masonry structure is anticipated under axial and flexural loading. The structural investigations and engineering processes are completed by the development of a package of dry-stacked units consisting of interlocking modular masonries and an accompanying array of various other precast parts. This confirmed the practical issues and solutions towards the exploitation of the developed dry-stacked elements for the construction of ready-to-build, modular and load-bearing walls. The portion of work presented herein proposes a new numerical technique for the determination of stress-percolation in dry stacked load-bearing structures. The model is developed in three steps under a numerical computing environment. First, based on geometrical properties of the dry-stacked elements and with a linear-elastic material behaviour, the load percolation and intensity in dry-stacked masonry walls is determined. In a second step, a phenomenon known as a plastic accommodation which accompanies the redistribution of the stress percolations, is incorporated in the model. This enables the understanding of the evolution of the stress percolations in the post-elastic phase, which is crucial for the determination of the load capacity and stability of the structure in function of an increased external load. This paper also supports the better understanding of early fissuring in dry-stacked masonry structures which has an important influence on the overall stability of the structure. Finally, in a third step, the improvement of dry-stacked structures is pursued by further analysis of the results obtained through the algorithm. This paper represents a new tool for investigating the localized and randomly defined internal stress distribution induced by external compression forces on dry-stacked structures. Furthermore, the algorithm illustrates that experimental investigations on dry-stacked systems may only give real indications on the load capacity of the structure, when the number of joint interfaces and height to length ratio of the block is respected and that results of experimental investigations on reduced prism specimens may not be extrapolated to full sized walls as they may over-evaluate the effective loaded masonry sections and therefore the overall load capacity. [less ▲]

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See detailResearch for sustainable construction
Waldmann, Danièle UL; Poulles, Romain

in Science and Technology (2016)

Detailed reference viewed: 61 (9 UL)
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See detailMasonry blocks from lightweight concrete on the basis of Miscanthus as aggregates
Waldmann, Danièle UL; Thapa, Vishojit Bahadur UL; Dahm, Franz et al

in Barth, S; Murphy-Bokern, D; Kalinina, O (Eds.) et al Perennial Biomass Crops for a Resource Constrained World (2016)

Detailed reference viewed: 94 (34 UL)