02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access Design of adhesively bonded timber-concrete composites : bondline properties(2023) Grönquist, Philippe; Müller, Katharina; Mönch, Simon; Frangi, AndreaItem Open Access Erläuterung der neuen Bewehrungsrichtlinien DIN 1045, Abschnitt 18, Ausgabe 12/78(1979) Rehm, Gallus; Eligehausen, Rolf; Neubert, BerndDie Neubearbeitung hatte zum Ziel, die "Mängel" der bisherigen Fassung zu beseitigen und Regeln für den "Normalfall" zu schaffen, die das Konstruieren erleichtern und die Rationalisierung der Bewehrungsarbeiten fördern. Bei der Bearbeitung wurde davon ausgegangen, da8 die Norm keine "Kochrezepte" liefern kann, die in allen vorkommenden Fällen ohne Detailkenntnisse angewandt werden können und die dabei gleichzeitig das jeweils technisch Machbare beinhalten. Vielmehr wurde vorausgesetzt, daß alle in der Praxis tätigen Ingenieure einen ausreichenden Sachverstand besitzen, um die angegebenen Regeln den jeweiligen Gegebenheiten unter Beachtung der Prinzipien des Stahlbetonbaus anzupassen.Item Open Access Analysis of headed anchors embedded in concrete using a nonlinear fracture model(1992) Sawade, Gottfried; Eligehausen, RolfThis paper represents an energetical model of the fracture behaviour of concrete where crack opening is considered as time dependent dissipative process. States of mechanical equilibrium can be obtained by simulation of a relaxation process. Applicatlon of this model to calculations of the bearing capacity of anchorages confirms recent approachs based on linear fracture mechanics.Item Open Access Variation of mechanical properties in oak boards and its effect on glued laminated timber : application to a stochastic finite element glulam strength model(Göttingen : Cuvillier Verlag, 2022) Tapia Camú, Cristóbal; Garrecht, Harald (Prof. Dr.-Ing.)The renewable material wood and hereof derived structural engineered wood products (EWPs) is widely acknowledged as being the major pillar of sustainable building construction. Due to the strongly increasing demand and technical assets the wood resource hardwoods, previously less used as compared to softwoods, is gaining a high momentum for EWPs. Here, the species white oak (Quercus robur, petraea) representing beside beech (Fagus sylvatica) the largest hardwood stocks in Europe is investigated. This work addresses the need of improved understanding and modeling of the variability of stiffness and strength along and between boards and the resulting impact on the size-effect of glued laminated timber (GLT) made of oak. A set of 53 oak boards (Quercus robur) was used to study the variation of mechanical properties along the board's main axis. For each board, detailed information regarding size and position of knots was obtained, which was then used to digitally reproduce the geometry of the knots. The modulus of elasticity (MOE) parallel to the fiber was measured in tension along each board in 15 consecutive segments of 100 mm in length. The boards were tested in tension until failure and the remnants were then tested in secondary tension tests, when possible. Thus, multiple values for tensile strength were obtained per board. Based on the MOE results, a first order autoregressive [AR(1)] model for the simulation of local MOE profiles within board was developed. The model considers the non-stationarity of the MOE profiles by means of a two step method. Firstly, a Gaussian AR process is conducted and then mapped to the normalized MOE distribution. In a second step, the result in scaled to fit a specified global MOE value. The tensile strength data was analyzed by means of survival analysis, where different parametric and regression type statistical models were fitted. The tensile strength models were coupled to the localized MOE AR(1) model by means of a cross-correlation coefficient, thus obtaining a modified vector autoregressive (VAR) model for the local MOE and tensile strength along board. Numerical simulations with the fitted tensile strength models predicted a relatively high size effect, i.e. length effect, characterized by a size-effect exponent of around 0.23 at the 5%-quantile level. A stochastic finite element model for the analysis of GLT beams was developed. The model considers the local variation of mechanical properties within each lamination, simulated by the derived VAR model, as well as the stochastic distribution of finger-joints connecting adjacent boards. A simple energy-based failure mechanism is considered for the evolution of tensile damage in wood and finger-joint elements. The model was calibrated with experiments of oak GLT beams of three different cross-sections tested at the MPA, University of Stuttgart, and then applied to simulate a second database of oak GLT beams tested at FCBA, France. The results obtained with the model are in good agreement with the experiments. In particular, the size effect of beam depth is correctly represented. The influence of the used material models for wood and finger-joints was analyzed parametrically. It is shown that the lower tail of the local tensile strength distribution, which can be estimated rather accurately by survival analysis dominates the GLT bending strength. This is fortunate, as the lower tails can be estimated by means of survival analysis in a rather accurate manner, while the upper tails require further assumptions. The author hopes that the presented work contributes to stimulate the discussion on modelling of structural timber elements made of hardwoods.Item Open Access Performance-oriented design and assessment of naturally ventilated buildings(2021) Sakiyama, Nayara R. M.; Garrecht, Harald (Prof.)A high-performance building must fulfill comfort and energy efficiency requirements. Possible solutions include passive strategies, such as improving the building envelope and taking advantage of natural light and ventilation. Natural ventilation (NV), for instance, can provide both thermal comfort and energy savings. However, its performance relies on building design and interaction with the local environmental characteristics. In this study, Natural Ventilation Potential (NVP) was analyzed under two approaches: a general evaluation using meteorological data and a specific investigation through building simulation, using an experimental house as a reference case located in a temperate climate with warm summer. Although there are many parameters and metrics applied in assessing NVP, predicting building air change rates (ACH) and airflows is a challenge for designers seeking to deal with this passive strategy. Among the methods available for this task, Computational Fluid Dynamics (CFD) appears as the most compelling, in ascending use. However, CFD simulations have high computational costs, besides requiring a range of settings and skills that inhibit its wide application. Therefore, a pragmatic CFD framework to promote wind-driven assessments through 3D parametric modeling platforms was proposed as an attractive alternative to enable the tool application. The approach addresses all simulation steps: geometry and weather definition, model set-up, control, results edition, and visualization. Besides, it explores alternatives to display and compute ACH and parametrically generates horizontal planes across the spaces to calculate surface average air velocities. Usually, network models throughout Building Energy Simulation (BES) are the most employed NV investigations approach, especially in annual analysis. Nevertheless, as the wind is a significant driving force for ventilation, wind pressure coefficients (Cp) represent a critical boundary condition when assessing building airflows, influencing BES models’ results. The Cp values come from either a primary source that includes CFD simulations or a secondary one where the primary is considered the most reliable. In this sense, a performance metric was proposed, namely the Natural Ventilation Effectiveness (NVE). It verifies when outdoor airflows can maintain indoor temperatures within a comfortable range. The metric uses BES results, and within this context, the impact of five different Cp sources on its outputs was investigated. Three secondary sources and surface-averaged Cp values calculated with CFD for both the whole façade and windows were considered. The differences between the CFD Cp values are minor when wind direction is normal to the surface, with more significant discrepancies for the openings close to roof eaves. Although there was considerable variance among the Cp sources, its effect on the NVE was relatively small. Additionally, when designing high-performance buildings for cold climates, efficient insulating systems are encouraged since they help reduce heat losses through the building envelope, thus promoting building energy savings. Still, climate exposure deteriorates material properties, compromising a building’s energy performance over its lifetime. Therefore, this aging impact on the hygrothermal performance of an aerogel-based insulating system was investigated through a large-scale test, U-Value measurements, and heat and moisture transfer (HMT) models, calibrated with the experimental data. A low thermal conductivity degradation was measured after the tests, showing that its effectiveness is not harshly compromised throughout its life-cycle. Finally, this research performed parametric modeling and optimization to minimize annual building energy demand and maximize NVE. The workflow was divided into i) model setting, ii) sensitivity analyses (SA), and iii) multi-objective optimization (MOO), with a straightforward process implemented through a parametric platform. Input variables dimension was firstly reduced with SA, and the last step ran with a model-based optimization algorithm (RBFOpt). MOO results showed a remarkable potential for NV and heating energy savings. The design solutions could be employed in similar typologies and climates, and the adopted framework configures a practical and replicable approach for design approaches aiming to develop high-performance buildings through MOO.Item Open Access Doktorandenkolloquium Holzbau Forschung + Praxis : Stuttgart, 18. + 19. März 2024(2024) Kuhlmann, Ulrike; Grönquist, Philippe; Tapia, Cristóbal; Buchholz, LeaItem Open Access Auswirkungen der modemen Befestigungstechnik auf die konstruktive Gestaltung im Stahlbetonbau(1984) Rehm, Gallus; Eligehausen, RolfDie wenigen Beispiele zeigen, daß mit der Entwicklung der Befestigungstechnik neue Probleme entstanden sind. Bisher wurden diese Probleme bei der Ableitung der Stahlbetonrichtlinien nicht beachtet. Daher war es erforderlich, die Regeln für Befestigungen so festzulegen, daß keine wesentliche Beeinflussung des Bauteiltragverhaltens zu erwarten war. Um dies zu gewährleisten, wird verlangt, daß Verankerungen nur in der aus Lastspannungen erzeugten Druckzone von Stahlbetonbauteilen angeordnet bzw. nur sehr geringe Lasten in großen Abständen in die Zugzone eingeleitet werden. Diese Regelung ist praxisfremd, weil der die Befestigung Ausführende die genaue Lage der Druckzone im Bauwerk nicht kennt. Weiterhin schränkt sie die Möglichkeiten der Befestigungstechnik ein. Will man diese Möglichkeiten voll ausnutzen, muß der Einfluß der speziellen Lasteinleitung durch Befestigungselemente bei der Ableitung von Konstruktionsregeln für Stahlbetonbauteile berücksichtigt werden, um auch weiterhin ausreichend sichere Bauwerke zu gewährleisten. Dabei sind z. B. Einschränkungen für die Ausbildung von Übergreifungsstößen, für die Anwendung von offenen Bügeln und für die Bemessung von auf Schub unbewehrten Platten zu erwarten.Item Open Access Geklebte Verbindungen von Brettsperrholz-Platten in der Nebentragrichtung unter Verwendung von CNC/ robotisch gefrästen Anschlussleisten aus Furnierschichtholz(2020) Claus, MarianIm Zuge dieser Arbeit wird sich mit der Entwicklung einer geklebten Brettsperrholzplattenverbindung in Nebentragrichtung beschäftigt. Die Verbindung soll es ermöglichen, vorgefertigte Brettsperrholzplattenelemente baustellenseitig so miteinander zu verbinden, dass sie in Nebentragrichtung Momente übertragen können. Dies soll die Leistungsfähigkeit des verwendeten Systems steigern und dem Planer neue Möglichkeiten im Entwurf bieten. Die Verbindung wurde zunächst analytisch betrachtet und weiterentwickelt und anschließend mit der FE-Software Abaqus untersucht und optimiert. Um die Simulation zu validieren und die Verbindung in der Praxis zu testen wurde die Verbindung in Kooperation mit dem IfW hergestellt und an der MPA in Form von 4-Punkt-Biegeversuchen getestet.Item Open Access Erläuterungen zu DIN 4227, Abschnitt 10(1980) Rehm, Gallus; Eligehausen, RolfDurch die in Abschnitt 10 geforderten Nachweise soll ein befriedigendes Verhalten von Spannbetonbauteilen im Gebrauchszustand durch Beschränkung der Breite von eventuell auftretenden Rissen gewährleistet werden.Item Open Access Bond of ribbed bars under high cycle repeated loads(1979) Rehm, Gallus; Eligehausen, RolfTo determine the bond behavior of ribbed bars under repeated loads, 308 pullout specimens were tested. The specimens failed by pulling out of the bars. In the tests the following parameters were varied: maximum load and load amplitude, bar diameter, concrete quality, and bond Iength. Furthermore, as a comparison, tests under sustained load were carried out. A repeated load has a similar influence on the bond as on the deformation and failure behavior of unreinforced concrete, and it accelerates, in comparison with a sustained load, the nonelastic deformation (slip).