02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access Heat transport from atmosphere through the subsurface to drinking‐water supply pipes(2023) Nissler, Elisabeth; Scherrer, Samuel; Class, Holger; Müller, Tanja; Hermannspan, Mark; Osmancevic, Esad; Haslauer, ClausDrinking‐water quality in supply pipe networks can be negatively affected by high temperatures during hot summer months due to detrimental bacteria encountering ideal conditions for growth. Thus, water suppliers are interested in estimating the temperature in their distribution networks. We investigate both experimentally and by numerical simulation the heat and water transport from ground surface into the subsurface, (i.e., above drinking‐water pipes). We consider the meteorological forcing functions by a sophisticated approach to model the boundary conditions for the heat balance at the soil-atmosphere interface. From August to December 2020, soil temperatures and soil moisture were measured dependent on soil type, land‐use cover, and weather data at a pilot site, constructed specifically for this purpose at the University of Stuttgart with polyethylene and cast‐iron pipes installed under typical in situ conditions. We included this interface condition at the atmosphere-subsurface boundary into an integrated non‐isothermal, variably saturated (Richards') the numerical simulator DuMux 3. This allowed, after calibration, to match measured soil temperatures with ±2°C accuracy. The land‐use cover influenced the soil temperature in 1.5 m more than the soil material used for back‐filling the trench above the pipe.Item Open Access Batch studies of phosphonate and phosphate adsorption on granular ferric hydroxide (GFH) with membrane concentrate and its synthetic replicas(2020) Reinhardt, Tobias; Veizaga Campero, Adriana Noelia; Minke, Ralf; Schönberger, Harald; Rott, EduardPhosphonates are widely used as antiscalants for softening processes in drinking water treatment. To prevent eutrophication and accumulation in the sediment, it is desirable to remove them from the membrane concentrate before they are discharged into receiving water bodies. This study describes batch experiments with synthetic solutions and real membrane concentrate, both in the presence of and absence of granular ferric hydroxide (GFH), to better understand the influence of ions on phosphonate and phosphate adsorption. To this end, experiments were conducted with six different phosphonates, using different molar Ca:phosphonate ratios. The calcium already contained in the GFH plays an essential role in the elimination process, as it can be re-dissolved, and, therefore, increase the molar Ca:phosphonate ratio. (Hydrogen-)carbonate ions had a competitive effect on the adsorption of phosphonates and phosphate, whereas the influence of sulfate and nitrate ions was negligible. Up to pH 8, the presence of CaII had a positive effect on adsorption, probably due to the formation of ternary complexes. At pH > 8, increased removal was observed, with either direct precipitation of Ca:phosphonate complexes or the presence of inorganic precipitates of calcium, magnesium, and phosphate serving as adsorbents for the phosphorus compounds. In addition, the presence of (hydrogen-)carbonate ions resulted in precipitation of CaCO3 and/or dolomite, which also acted as adsorbents for the phosphorus compounds.Item Open Access High-resolution spatio-temporal measurements of the colmation phenomenon under laboratory conditions(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2022) Mayar, Mohammad Assem; Wieprecht, Silke (Prof. Dr.-Ing.)The fine sediment infiltration and accumulation into the gravel bed of rivers, the so-called colmation phenomenon, is a pernicious process exacerbated by anthropogenic activities. Owing to the importance and complexity of this phenomenon, it has been widely studied over the last decades. Various devices and methods have been developed to assess this phenomenon, where most of them are destructive and sample-based, resulting in an alteration of the natural conditions. Therefore, non-intrusive techniques, which provide spatial and temporal details with a high-resolution, are required to discretize the mechanisms involved in the colmation process. To address these issues, investigations under laboratory conditions may simplify the complexity of nature and enable individual and exactly defined boundary conditions to be investigated. Therefore, this thesis aims at (i) developing a non-intrusive and undisturbed measurement method for the high-resolution spatio-temporal measurements of the sediment infiltration processes and the development of sediment accumulation in an artificial river bed under laboratory conditions, (ii) applying this method to certain experiments for the assessment of the effects of different boundary conditions on sediment infiltration, and (iii) investigating the colmation phenomenon (also known as clogging) of gravel beds. For this purpose, the gamma-ray attenuation method is used together with an artificial gravel bed arranged from the spheres with various diameters and placed in a laboratory flume. This new method works based on the gamma radiation that passes through the infiltrated sediments, water, and bed spheres, in which the gamma-ray attenuation is linked to the variations of the infiltrated sediments’ quantity. The main simplification of this approach is that gravel beds are represented by the combinations of different-sized spheres. This gives the opportunity to fully distinguish infiltrating sediments from the bed material, reduce the complexity of the natural environment, and allows for repetitive measurements of the same position with different boundary conditions. From the results of this study, first, the gamma-ray attenuation measurement method was optimized to resolve the inconsistencies in the measurements. Subsequently, the concept of the non-intrusive and undisturbed measurement is proved through box experiments. Additional reproducibility experiments in the laboratory flume, for a similar bed structure, showed only small deviations between two experiments with the same setup. Consequently, the established technique was used in a series of experiments to evaluate the effects of different supply rates, total supply masses, and sediment particle size boundary conditions on the sediment infiltration and colmation processes. Vertical profiles of the infiltrated sediment were quantified through high spatial resolution measurements. Furthermore, to evaluate the infiltrating sediment accumulation development, and the temporal variations of the infiltrated sediments, the vertical profile measurements were first repeated after a specific time-period to track interval-averaged variations in all positions of the vertical axis. Next, a specific position of the vertical axis was measured continuously during the entire experiment in a high temporal resolution. The measured vertical profiles illustrate the vertical distribution, colmation, and unimpeded percolation of the infiltrated sediments. The dynamic one-point measurement precisely identifies the three phases (the start of the pore-filling, the required time to fill the pore, and the final amount of infiltrated sediments including natural fluctuation during the ongoing experiments) of the sediment infiltration or the possible clogging. As a limitation, the gamma-ray attenuation system’s current configuration only works in artificial gravel beds because of the given density difference between infiltrated sediments and the artificial bed structure. Intense radiations that pass through the natural bed's thickness are capable of detecting a significant amount of infiltrated sediments. However, small amounts of infiltrated sediments will create only a minimal shift in attenuation, which might be confused with the statistical error. In addition, the legal restriction against using radioactive material in the natural environment is another reason for not applying it in the field. Furthermore, the gamma-ray attenuation method cannot resolve the sediment distribution in the measurement horizon and provides an integrative result for each measurement position. In addition, if a mixture of silt, clay, and sand is supplied to the experiment, the gamma-ray attenuation system will produce a bulk result of all the infiltrated materials. To conclude, despite the limitations mentioned above, the gamma-ray attenuation method offers a unique opportunity for the non-intrusive and undisturbed measurements of the sediment infiltration or the special case of colmation, with a high spatio-temporal resolution. This method has the potential to quantify the investigated processes on a millimetric spatial scale, if the measurement time is not a constraint, or vice versa, in a high temporal resolution (seconds) for a specific position, if spatial scale is not important. Moreover, the gamma-ray attenuation approach can simultaneously measure the longitudinal distribution of the sedimentological processes, if multiple instruments or a single device with several radiation-emitting-holes is in operation. Last, but not least, rather than the spheres, artificial gravel beds could be made of any substance with a composition significantly different from the infiltrating sediments, and the boundary conditions of the experiments can be improved in order to attain conditions close to nature. Finally, the gamma-ray attenuation method can be integrated with advanced flow measurement instruments such as Particle Image Velocimetry (PIV) and other high-resolution endoscopic devices to track the behavior of fine sediment infiltration and its clogging process in the porous gravel beds as it occurs in nature.Item Open Access Guidelines for a finite element based design of timber structures and their exemplary application on modelling of beech LVL(2023) Töpler, Janusch; Buchholz, Lea; Lukas, Julian; Kuhlmann, UlrikeDesign verifications of buildings are usually carried out supported by a finite element analysis (FEA), for which, however, there are only a few and almost exclusively non-binding application rules. Within the Cluster of Excellence Integrative Computational Design and Construction for Architecture (IntCDC) at the University of Stuttgart, Guidelines for a Finite Element-Based Design of Timber Structures have been developed. The scope of the guidelines is daily engineering practice, expert engineering applications and product development and certification. Essential parts of the guidelines are design procedures, modelling (including geometrical, material and imperfection modelling), analysis, model verification and validation and design. The content and application of the guidelines are described and illustrated in this paper using two benchmarks. These two benchmarks, which are based on experimental investigations, deal with the elastic material modelling of glulam made of beech laminated veneer lumber (beech LVL) and dowel-type connections for beech LVL members. The experimental basis of the benchmarks is described. With the experiments for the benchmarks, all Poisson’s ratios and the complete elastic material stiffness matrix of beech LVL are determined by means of an optical measuring system. The experimentally determined stiffnesses of the investigated dowel-type connections in beech LVL are compared with normative values. Based on the experiments, a numerical model is developed in RFEM (Dlubal).Item Open Access Magnetic resonance imaging of water content and flow processes in natural soils by pulse sequences with ultrashort detection(2021) Haber-Pohlmeier, Sabina; Caterina, David; Blümich, Bernhard; Pohlmeier, AndreasMagnetic resonance imaging is a valuable tool for three-dimensional mapping of soil water processes due to its sensitivity to the substance of interest: water. Since conventional gradient- or spin-echo based pulse sequences do not detect rapidly relaxing fractions of water in natural porous media with transverse relaxation times in the millisecond range, pulse sequences with ultrafast detection open a way out. In this work, we compare a spin-echo multislice pulse sequence with ultrashort (UTE) and zero-TE (ZTE) sequences for their suitability to map water content and its changes in 3D in natural soil materials. Longitudinal and transverse relaxation times were found in the ranges around 80 ms and 1 to 50 ms, respectively, so that the spin echo sequence misses larger fractions of water. In contrast, ZTE and UTE could detect all water, if the excitation and detection bandwidths were set sufficiently broad. More precisely, with ZTE we could map water contents down to 0.1 cm3/cm3. Finally, we employed ZTE to monitor the development of film flow in a natural soil core with high temporal resolution. This opens the route for further quantitative imaging of soil water processes.Item Open Access Phase-field modeling of microstructure and fracture evolution in magneto-electro-mechanics(Stuttgart : Institute of Applied Mechanics, 2020) Sridhar, Ashish; Keip, Marc-André (Prof. Dr.-Ing.)Item Open Access Bewertung der Ermüdungsfestigkeit von geschweißten und gelöteten Lamellen, Steifen und Anbauteilen(Stuttgart : Institut für Konstruktion und Entwurf, 2022) Drebenstedt, Karl; Kuhlmann, Ulrike (Prof. Dr.-Ing.)Die Ermüdungsfestigkeit von geschweißten Konstruktionen beeinflusst maßgeblich die Lebensdauer von zyklisch beanspruchten Stahlkonstruktionen. Durch Kerbwirkung und daraus resultierenden Spannungskonzentrationen entstehen im Bereich der Schweißnähte Ermüdungsrisse, die zum Versagen einer Konstruktion führen können und folglich in der Bemessung berücksichtigt werden müssen. Die Lebensdauer, die als Anzahl der Schwingspiele bis zum Versagen dargestellt werden kann, ist abhängig von der zyklischen Beanspruchung und der ihr gegenüberstehenden detailspezifischen Ermüdungsfestigkeit. Das Ziel der vorliegenden Arbeit ist die empirisch gestützte Bewertung der Ermüdungsfestigkeit von Anbauteilen, die auf eine zyklisch beanspruchte Stahlkonstruktion aufgeschweißt oder aufgelötet werden, selbst aber keiner direkten Ermüdungsbeanspruchung ausgesetzt sind. Trotz ihrer im Sinne der Lastabtragung häufig untergeordneten Bedeutung werden diese Schweißdetails für die Ermüdungsbemessung regelmäßig bemessungsmaßgebend und bestimmen damit auch die Dimensionierung der Haupttragstruktur. Konkret werden die Ermüdungsfestigkeiten von Lamellen, Längs- und Quersteifen, Schweißbuchsen, Kopfbolzen, Schweißtellern und von ähnlichen Details untersucht. Zu den genannten Konstruktionsdetails wurden in einer sehr umfangreichen Datenbank über 8.000 Versuchsergebnisse aus veröffentlichten Studien zur Ermüdungsfestigkeit zusammengetragen. Das Datenbanksystem gewährleistet das gezielte Bearbeiten und Abfragen unterschiedlicher Informationen zu den Ermüdungsversuchen. Dies sind neben den Versuchsergebnissen und der Anzahl der erreichten Schwingspiele unter einer bestimmten zyklischen Beanspruchung Parameter wie technische Materialeigenschaften und geometrische Spezifikationen. Zusätzlich zu den in der Datenbank gesammelten Versuchsergebnissen wurden eigene Ermüdungsversuche an Konstruktionsdetails durchgeführt. Konkret untersucht wurde unter anderem die traditionelle deutsche Variante des Konstruktionsdetails Gurtlamellenende. Die vorzugsweise im Brückenbau verbreitete Form des Gurtlamellenendes mit verstärkter Stirnnaht und kerbfrei bearbeiteten Nahtübergängen zeigt deutlich höhere Ermüdungsfestigkeiten als die einfache Variante mit umlaufender Kehlnaht im Schweißzustand. Ein Schwerpunkt der experimentellen Untersuchungen liegt auf der Bewertung der Ermüdungsfestigkeit von Anbauteilen, die mit dem Kupferlot CuAl7 in einem Lichtbogenlötverfahren auf zyklisch beanspruchte Stahlkonstruktionen aufgelötet werden. In vielen Ermüdungsversuchen wurden das Verhalten und die Ermüdungsfestigkeit dieses alternativen Verfahrens zum Schweißen untersucht. Es kann gezeigt werden, dass die Ermüdungsfestigkeit von lichtbogengelöteten Anbauteilen eine deutlich höhere Ermüdungsfestigkeit bei vergleichbarer Versagenscharakteristik und vergleichbarer statischer Beanspruchbarkeit aufweist. Sowohl die in der Datenbank dokumentierten Versuche als auch die durchgeführten eigenen experimentellen Untersuchungen weisen infolge von unterschiedlichen Einflüssen auf die Ermüdungsversuche eine erhebliche Streuung auf. Für die Bewertung von Einflüssen auf die Lebensdauer und für die Ermittlung einer charakteristischen Ermüdungsfestigkeit, die einen statistisch abgesicherten Bemessungswert darstellt, muss diese Streuung berücksichtigt werden. Im Rahmen dieser Arbeit werden Verfahren zur statistischen Bewertung und Auswertung von Ermüdungsversuchen vorgestellt, die auf gemeinsamen statistischen Ansätzen beruhen und konform zu normativen Regelungen und Anforderungen im Bauwesen sind. Es kann gezeigt werden, dass die vorgestellte statistische Auswertemethode geeignet ist, zuverlässig statistisch abgesicherte Ermüdungsfestigkeiten für einzelne Serien oder für Metaanalysen mit mehreren 1.000 Versuchsergebnissen abzuleiten. Die eigenen experimentellen Untersuchungen und die Vielzahl der in der Datenbank aufgearbeiteten Versuchsergebnisse ermöglichen in Kombination mit der einheitlichen statistischen Auswertemethode Metastudien. Unterschiede können sich sowohl auf technische Aspekte beziehen wie Fertigungseinflüsse, Schweißtechnik, mechanische Materialeigenschaften und Versuchsumsetzung, als auch auf Randbedingungen wie beispielsweise die verwendete Prüf- und Messtechnik. Die Bewertung von Ermüdungsfestigkeiten für bestimmte Konstruktionsdetails auf Grundlage der Vielzahl der zur Verfügung stehenden Versuchsdaten ermöglicht damit die Berücksichtigung eines Spektrums von potenziellen Einflussfaktoren auf die charakteristische Ermüdungsfestigkeit. Die in den Versuchen ermittelten Ermüdungsfestigkeiten werden verglichen mit Ergebnissen aus numerischen Untersuchungen mit dem Kerbspannungsmodell. Dafür wurden einige Konstruktionsdetails mit dem Kerbspannungsmodell dreidimensional nachgebildet und validiert. Die Modelle eignen sich für Parameterstudien zu strukturmechanischen Einflussgrößen und geben geometrische Einflüsse tendenziell gut wieder. Die Untersuchungen zeigen auch, dass geometrische Einflüsse auf die Ermüdungsfestigkeit bei Verwendung des Kerbspannungsmodells überschätzt werden können. Als ursächlich dafür werden Streuungen aus Fertigungseinflüssen vermutet, die einen maßgeblichen Einfluss auf die Kerbwirkung haben können. Es wird anhand von vergleichenden Streuspannen für Konstruktionsdetails und Gruppen von Konstruktionsdetails zudem gezeigt, dass das Kerbspannungskonzept im Vergleich zum Nennspannungskonzept im Sinne der Bemessung nicht das genauere Verfahren zur Ermüdungsbemessung von Anbauteilen darstellt. Auf Grundlage der Untersuchungen und Erkenntnisse werden am Ende dieser Arbeit konkrete Bemessungsvorschläge für die Bewertung der Ermüdungsfestigkeit mit dem Nennspannungskonzept für geschweißte und gelötete Anbauteile wie Lamellen, Längs- und Quersteifen, Schweißbuchsen, Kopfbolzen und Schweißteller gegeben.Item Open Access Update on the revision of Eurocode 3 : evolution by improvement and harmonization(2021) Kuhlmann, Ulrike; Schmidt‐Rasche, Christina; Jörg, Fabian; Pourostad, Vahid; Spiegler, Jennifer; Euler, MathiasThis paper provides an overview of recent work regarding the revision of Eurocode 3 on the European level. Selected scientific and technical issues are described and there is a summary of the activities executed within European Standardization Committee CEN/TC250/SC3 ”Design of Steel Structures“ chaired by Prof. Dr.‐Ing. Ulrike Kuhlmann. This includes the description of current normative developments for the 2nd Generation of Eurocodes, which aim at evolution through improvements and harmonization of the existing codes. In addition, a technical review of selected rules is given for several issues, which support the code revision and reflect well the recent tendencies in steel structures.Item Open Access Impact of combined sewer systems on the quality of urban streams : frequency and duration of elevated micropollutant concentrations(2020) Dittmer, Ulrich; Bachmann-Machnik, Anna; Launay, Marie A.Water quality in urban streams is highly influenced by emissions from WWTP and from sewer systems particularly by overflows from combined systems. During storm events, this causes random fluctuations in discharge and pollutant concentrations over a wide range. The aim of this study is an appraisal of the environmental impact of micropollutant loads emitted from combined sewer systems. For this purpose, high-resolution time series of river concentrations were generated by combining a detailed calibrated model of a sewer system with measured discharge of a small natural river to a virtual urban catchment. This river base flow represents the remains of the natural hydrological system in the urban catchment. River concentrations downstream of the outlets are simulated based on mixing ratios of base flow, WWTP effluent, and CSO discharge. The results show that the standard method of time proportional sampling of rivers does not capture the risk of critical stress on aquatic organisms. The ratio between average and peak concentrations and the duration of elevated concentrations strongly depends on the source and the properties of the particular substance. The design of sampling campaigns and evaluation of data should consider these characteristics and account for their effects.Item Open Access Design recommendations for concrete pryout capacity of headed steel studs and post-installed anchors(2023) Jebara, Khalil; Sharma, Akanshu; Ožbolt, JoškoCurrent formulas to assess the shear capacity of headed steel stud anchors and post-installed (PI) anchors in case of pryout failure (sometimes known as pull-rear failure) have been derived either based on the indirect-tension resistance model or are fully empirical based on push-out test results. In both cases, the predicted pryout capacity is clearly conservative and underestimates the true pryout capacity of anchorages, especially for stiff anchors with low embedment-to-diameter ratios (hef/d < 4.5). This paper proposes an empirical and a semi-empirical formula to predict the concrete pryout capacity of headed steel studs and PI anchors. They were derived based on an improved indirect-tension model which accounts for the stud diameter and the stud spacing in a group of anchors. Furthermore, a database of 214 monotonic shear tests from the literature, including own tests (push-off and horizontally shear tests), is reevaluated and compared to the provisions of EN1992-4. The scope of this assessment proposal includes single and group of headed steel studs and PI anchors attached to a stiff steel plate as well as shear connectors in composite structures without metal deck embedded in normal-weight concrete.