The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely ...investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Early detection of fatigue cracks and accurate measurements of the crack growth play an important role in the maintenance and repair strategies of steel structures exposed to cyclic loads during ...their service life. Observation of welded connections is especially of high relevance due to their higher susceptibility to fatigue damage. The aim of this contribution was to monitor fatigue crack growth in thick welded specimens during fatigue tests as holistically as possible, by implementing multiple NDT methods simultaneously in order to record the crack initiation and propagation until the final fracture. In addition to well-known methods such as strain gauges, thermography, and ultrasound, the crack luminescence method developed at the Bundesanstalt für Materialforschung und -prüfung (BAM), which makes cracks on the surface particularly visible, was also used. For data acquisition, a first data fusion concept was developed and applied in order to synchronize the data of the different methods and to evaluate them to a large extent automatically. The resulting database can ultimately also be used to access, view, and analyze the experimental data for various NDT methods. During the conducted fatigue tests, the simultaneous measurements of the same cracking process enabled a comprehensive comparison of the methods, highlighting their individual strengths and limitations. More importantly, they showed how a synergetic combination of different NDT methods can be beneficial for implementation in large-scale fatigue testing but also in monitoring and inspection programs of in-service structures - such as the support structures of offshore wind turbines.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Monopiles are currently the predominant foundation type for offshore wind turbines in Europe. Due to the increasing dimensions of the turbines, pile diameters beyond 10m become necessary. A ...design‐relevant failure mode of monopiles is the local buckling of the pile wall in the embedded sections. Relevant buckling guidelines do not consider the soil‐structure interaction specifically, although the embedment may allow for a reduction of wall thickness. However, Eurocode‐based design concepts require a validation with comparative buckling cases for validation, either in terms of buckling curve parameters for both the algebraic stress‐based and semi‐numerical LBA/MNA design concept or as a calibration factor kGMNIA for fully numerical GMNIA calculations. These parameters are not yet available for embedded shells. To close this gap, we have conducted experiments on piles embedded in sand to investigate local buckling under soil‐structure‐interaction. The results will be used to calibrate numerical models. This research was carried out as part of the VERBATIM research project, funded by PTJ/BMWK and supported by the Carbon Trust's Offshore Wind Accelerator consortium.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
•A constitutive damage model for concrete under compressive fatigue is presented.•The model is based on a viscous formulation which induces damage.•Fatigue and creep are combined in a single ...constitutive framework.•The model is validated using triaxial compression, creep and fatigue tests.•Realistic simulation of the Wöhler-curve is demonstrated.
Conventional approaches to model fatigue failure are based on a characterization of the lifetime as a function of the loading amplitude. The Wöhler diagram in combination with a linear damage accumulation assumption predicts the lifetime for different loading regimes. Using this phenomenological approach, the evolution of damage and inelastic strains and a redistribution of stresses cannot be modeled. The gradual degration of the material is assumed to not alter the stress state. Using the Palmgren–Miner rule for damage accumulation, order effects resulting from the non-linear response are generally neglected.
In this work, a constitutive model for concrete using continuum damage mechanics is developed. The model includes rate-dependent effects and realistically reproduces gradual performance degradation of normal strength concrete under compressive static, creep and cyclic loading in a unified framework. The damage evolution is driven by inelastic deformations and captures strain rate effects observed experimentally. Implementation details are discussed. Finally, the model is validated by comparing simulation and experimental data for creep, fatigue and triaxial compression.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Bei Monopfahlgründungen von Offshore‐Windenergieanlagen wird die Verbindung zwischen Monopfahl und Übergangsstück als geschraubter Ringflansch ausgeführt. Die zunehmende Leistungsfähigkeit der ...Windenergieanlagen führt zu immer größeren Schnittgrößen in diesem Anschluss. In der Folge erhöhen sich nicht nur die Querschnittsabmessungen, sondern es kommen auch zunehmend größere Schrauben zum Einsatz. Da die einschlägigen Regelwerke zur Bemessung dieser Verbindungen nicht für Schrauben der Größen M64 oder M72 konzipiert wurden, stellt sich die Frage der Übertragbarkeit auf solche Anwendungsfälle. Im Rahmen des Aufsatzes werden Einflüsse diskutiert, die eine Herabsetzung der Schraubentragfähigkeit verursachen könnten. Diese Einflüsse, vornehmlich geometrische Imperfektionen, werden systematisch untersucht und ergänzend in praxisrelevanten Beispielen bewertet. Die somit gewonnenen Erkenntnisse werden für die abschließende Beurteilung der großen Schrauben in Ringflanschverbindungen herangezogen.
Factors influencing the pretension force in bolts with diameter up to M72 in ring flange connections. The joint between monopile and transition piece in monopile foundations of offshore wind turbines is realized by bolted ring flanges. The increased size of the wind turbines leads to ever larger internal forces at this joint. This does not only cause an increase in cross sectional dimensions, but also requires the use of larger bolts. Since the relevant regulations for the verification of this joint type were not devised for bolts of size M64 or even M72, the applicability of these rules is challenged. Therefore, influences that may have the potential to lower the strength of these bolts are discussed in this work. These influences, primarily geometric imperfections, are systematically investigated and additionally evaluated with realistic examples. The findings from these analyses are used to give a final assessment for the use of large bolts in bolted ring flanges.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Conventional non-destructive testing methods for crack detection provide just a snapshot of fatigue crack evolution at a specific location in the moment of examination. The crack luminescence coating ...realizes a clear visibility of the entire crack formation. The coating consists of two layers with different properties and functions. The bottom layer emits light as fluorescence under UV radiation. The top layer covers the fluorescing one and prevents the emitting of light in case of no damage at the surface. Several different experiments show that due to the sensitive coating even the early stage of crack formation can be detected. That makes crack luminescence helpful for investigating the incipient crack opening behavior. Cracks can be detected and observed during operation of a structure, making it also very interesting for continuous monitoring. Crack luminescence is a passive method and no skilled professionals are necessary to detect cracks, as for conventional methods. The luminescent light is clearly noticeable by unaided eye observations and also by standard camera equipment, which makes automated crack detection possible as well. It is expected that crack luminescence can reduce costs and time for preventive maintenance and inspection.
Abstract
Bei Monopfahlgründungen von Offshore‐Windenergieanlagen wird die Verbindung zwischen Monopfahl und Übergangsstück als geschraubter Ringflansch ausgeführt. Die zunehmende Leistungsfähigkeit ...der Windenergieanlagen führt zu immer größeren Schnittgrößen in diesem Anschluss. In der Folge erhöhen sich nicht nur die Querschnittsabmessungen, sondern es kommen auch zunehmend größere Schrauben zum Einsatz. Da die einschlägigen Regelwerke zur Bemessung dieser Verbindungen nicht für Schrauben der Größen M64 oder M72 konzipiert wurden, stellt sich die Frage der Übertragbarkeit auf solche Anwendungsfälle. Im Rahmen des Aufsatzes werden Einflüsse diskutiert, die eine Herabsetzung der Schraubentragfähigkeit verursachen könnten. Diese Einflüsse, vornehmlich geometrische Imperfektionen, werden systematisch untersucht und ergänzend in praxisrelevanten Beispielen bewertet. Die somit gewonnenen Erkenntnisse werden für die abschließende Beurteilung der großen Schrauben in Ringflanschverbindungen herangezogen.
Abstract
Factors influencing the pretension force in bolts with diameter up to M72 in ring flange connections.
The joint between monopile and transition piece in monopile foundations of offshore wind turbines is realized by bolted ring flanges. The increased size of the wind turbines leads to ever larger internal forces at this joint. This does not only cause an increase in cross sectional dimensions, but also requires the use of larger bolts. Since the relevant regulations for the verification of this joint type were not devised for bolts of size M64 or even M72, the applicability of these rules is challenged. Therefore, influences that may have the potential to lower the strength of these bolts are discussed in this work. These influences, primarily geometric imperfections, are systematically investigated and additionally evaluated with realistic examples. The findings from these analyses are used to give a final assessment for the use of large bolts in bolted ring flanges.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
BACKGROUND: Intestinal Graft-versus-Host disease is a frequent and often lethal complication after allogenic stem cell transplantation. Since NOD2 polymorphisms have been recognized as potential ...triggers of severe intestinal GvHD in humans, we have developed murine transplantation models to investigate the role of different pattern recognition receptors (PRR) in GvHD and GvL. Here we report our results on the role of TLR2 and TLR4 for the induction of GvHD.
METHODS: Severity of GvHD in wildtype (wt) C57B/10 (H-2Db), TLR2−/−, TLR4−/−, and combined TLR2−/−TLR4−/− C57B/10 mice was investigated. Mice received treosulfan 2000 mg/kg from day -3 to -1 and cyclophosphamide 200 mg/kg day -1 prior to injection of 10×10^6 H-2Dd BM cells and 5×10^6 splenocytes (SC). Survival and GvHD score were assessed daily. Engraftment was determined every 2 weeks in pB and at the end of the experiments in bone marrow by flow cytometry. T cell alloreactivity in GvH direction was assessed by MLR using splenocytes as stimulators from PRR-deficient mice or wt as control and CFSE-staining as read-out. The relevance of PRR ligands for the enhancement of GvH alloreactivity was determined by addition of lipid A, lipopetides, or CpG.
RESULTS:
in vivo data: The transfer of 10×10^6 BMC + 5×10^6 SC induced a severe GvHD in all wt recipients, leading to death of 90% of the animals within 20 days. Recipient mice lacking either TLR2 or TLR4 showed only a slightly and not significantly decreased GvHD lethality. In recipients lacking both PPRs, i.e. TLR2 and TLR4, GvHD was generally milder and the majority (60%) of the animals survived until day 20 (p<0.05). However, the long term survival was not significantly improved. Differences in clinical severity of GvHD were confirmed histologically.In vitro data: Stimulation with cells from TLR2−/− and TLR4−/− mice resulted in a decreased alloreactivity in MLR. A median of 2% of Balb/c CD4+ T cells proliferated in response to C57B/10 stimulators. The addition of the TLR2 and TLR4 ligands lipopeptide, Lipid A and CpG significantly (p<0.05) increased the proliferation of CD4+ T cells in a specific manner more than twofold.
CONCLUSION: Our in vivo and in vitro data consistantly show that bacterial components are involved in triggering GvH alloreactivity via different types of PPRs. Binding of bacterial substances to TLR2 and TLR4 leads to activation of the immune system and subsequent induction of GvHD. Our data provide an experimental basis for the development of strategies for modulation of the intestinal gut flora by selective gut decontamination and/or probiotic regimens to prevent GvHD in humans.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
BACKGROUND: Treosulfan is increasingly used in clinical conditioning regimens because of its myeloablative and immunosuppressive effects and the low hepatotoxicity compared to busulfane. The ...myeloablative and immunosuppressive characteristics of treosulfane was investigated in a murine MHC mismatch transplantation model.
METHODS: C57BL/10 (H-2Db) female mice were treated with treosulfan (2000 mg/kg) on day -3 to -1 and increasing doses of cyclophosphamide (without, 100 or 200mg/kg) at day -1, or 3000 mg/kg treosulfan with and without 200 mg/kg cyclophosphamide at day -1. Some mice were not transplanted to examine the myeloablative effect of the regimens, the rest of mice were transplanted with 10 × 10^6 marrow cells from Balb/c mice (H-2Dd) donors and monitored for donor-type chimerism determined by flow cytometry.
RESULTS: Mice treated with treosulfan and cyclophosphamid without transplantation died, indicating the myeloablative effect of the regimens. Ca. 50% of mice treated with 3000 mg/kg treosulfan and 200 mg/kg cyclophosphamide at day -1 died. Analysis of bone marrow cells in the remaining mice showed a complete rejection at day 55. Approximately 90% of the recipients of three daily doses of treosulfan and increasing doses of cyclophosphamide survived until the end of experiment (day +100). All hosts engrafted when 200 mg/kg cyclophosphamide was applied. 85% of mice engrafted after 100mg/kg cyclophosphamide. 100% of grafts were rejected in the group with treosulfan alone (2000 mg/kg).
CONCLUSION: A chemotherapeutic regimen for achieving a long term survival in a MHC-mismatch situation without additional need of antibodies was established in mice. While investigated for the practicability in an animal model as alternative to TBI, the high rate of engraftments in a MHC mismatch situation makes the chemotherapeutic regimen suitable for clinical situations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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