02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access Finite element based design of timber structures(2023) Töpler, Janusch; Schweigler, Michael; Lemaître, Romain; Palma, Pedro; Schenk, Martin; Grönquist, Philippe; Tapia Camú, Cristóbal; Hochreiner, Georg; Kuhlmann, UlrikeItem Open Access Design of adhesively bonded timber-concrete composites : bondline properties(2023) Grönquist, Philippe; Müller, Katharina; Mönch, Simon; Frangi, AndreaItem Open Access Design for and from disassembly with timber elements : strategies based on two case studies from Switzerland(2023) Grüter, Cäsar; Gordon, Matthew; Muster, Marcel; Kastner, Fabian; Grönquist, Philippe; Frangi, Andrea; Langenberg, Silke; Wolf, Catherine deWhen a timber building gets disassembled and its elements either are burned or biodegrade, the carbon stored in the timber structure gets released to the atmosphere as CO2. Reusing timber elements prevents this process from happening and thus delays the global warming caused by greenhouse gas emissions. Even if there is a long historic tradition of timber reuse in Switzerland, currently a low fraction of a timber building’s elements is being reused after its disassembly. In this study, strategies that could facilitate circular use of timber elements are analyzed. The focus lies on the design process, which is investigated from two perspectives: strategies at the start-of-life of buildings to enable new timber element cycles to emerge (design for disassembly, or DforD), and strategies at the end-of-life of buildings to keep existing timber elements cycles closed (design from disassembly, or DfromD). Two case studies of recently completed multi-story timber-hybrid buildings in Switzerland were analyzed from both perspectives. Regarding DforD, a scoring system was developed that assesses single elements according to their disassembly and reuse potential. Regarding DfromD, a building design optimization tool was created that takes dimensional design tolerances of a building as an input and proposes a procurement-optimized and structurally safe arrangement of reused elements, which are taken from an inventory that is based on the two case studies. It was found that connections between reinforced concrete and timber parts play a crucial role in terms of DforD and that building layouts with DfromD elements may vary widely according to the chosen optimization variable. In conclusion, both applications have the potential to scale up the competitiveness of reused elements.Item Open Access Real-size structural health monitoring of a pre-stressed concrete bridge based on long-gauge fiber Bragg grating sensors(2021) Sakiyama, Felipe Isamu H.; Garrecht, Harald (Prof.)The ability to track the structural condition of existing structures is one of engineers, governments, and estate managers’ main con-cerns. In bridge maintenance programs, for example, visual in-spection predominates nowadays as the primary source of infor-mation. Nonetheless, visual inspections alone are insufficient to satisfy the current needs for structural safety assessment. The in-creasing demand for civil infrastructures, the aging of existing assets, and the strengthening of safety and liability laws have led to the inclusion of structural health monitoring (SHM) techniques into the structural management process. With the latest develop-ments in the sensors field and computational power, real-scale SHM deployment has become logistically and economically feasi-ble. However, it is still challenging to perform a quantitative evalua-tion of the structural condition based on measured data. Although the current approaches of SHM systems using traditional single-point sensors - such as electric strain sensors, accelerometers, and GPS-based sensors - have appropriate measurement precision for SHM purposes, they present challenges when deployed in real-scale applications, given the limited number of possible points to assess the structural behavior and the harsh environmental condi-tions during operation. When it comes to prestressed and rein-forced concrete structures, structural monitoring and damage identification present further challenges. They are affected by vari-ous chemical, physical and mechanical degradation processes and have a heterogeneous composition and non-linear behavior. On the other hand, fiber optic (FO) technology can provide integrated sensing in extensive measurement lengths with high sensitivity, durability, and stability, making them ideal for SHM of concrete structures. From this perspective, extensive research on structural health monitoring has been developed in the last decades. How-ever, the transfer rate from laboratory experiments to real-case applications is still unsatisfactory. This research addressed the main limitations that slow the deployment and the acceptance of real-size structural health monitoring systems in bridge mainte-nance programs. It proposed a long-term SHM concept to moni-tor prestressed concrete bridges, enabling the real-time detection of inherent damaging processes such as prestressing tendon break and crack opening and providing meaningful structural in-formation to support decision-making within bridge maintenance programs. An SHM system based on long-gauge fiber Bragg grat-ing (LGFBF) sensors was designed and deployed in a real-size prestressed concrete bridge. Autonomous and intelligent meas-urement tasks with data management and post-processing tools were implemented to operate the SHM system and delivery the expected results. A novel runtime algorithm for real-time analysis based on random variables correlation for condition monitoring was implemented to automatically detect unexpected events, such as local structural failure, within many random dynamic loads. Additionally, an integrated methodology for data interpretation and model updating built on data feature extraction using the principal component analysis (PCA), finite element (FE) modeling, and Monte Carlo simulations was proposed to identify existing damages and optimize the FE model updating process. The re-sults showed that the deployed SHM system successfully translates the massive raw data into meaningful information to access struc-tural response, predict damage formation, and calibrate a FE model of the monitored structure. Finally, the proposed real-time analysis algorithm delivers a reliable notification system that allows bridge managers to track unexpected events as a basis for deci-sion-making.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 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 Ermüdungsverhalten von Befestigungen in Beton bei überlagerter statischer Beanspruchung(2025) Fröhlich, Thilo; Hofmann, Jan (Prof. Dr.-Ing.)Im Bauwesen werden Befestigungselemente zur Verbindung von Stahlkonstruktionen mit Betonbauteilen u.a. für Aufzüge, Kranbahnträger und Schwenkkrane oder Maschinen verwendet, bei denen häufig wiederholte Beanspruchungen in Kombination mit einer statisch wirkenden Belastung auftreten, die zu einem Ermüdungsversagen des Befestigungspunkts führen können. Der bisherige Wissensstand zur Ermüdungstragfähigkeit von Befestigungen in Beton basiert im Wesentlichen auf Schwingversuchen im Schwellbereich mit geringer Unterlast, wobei die Versagensart Stahlbruch des Befestigungsmittels häufig maßgebend wird. Bei der Bemessung werden für Befestigungen unter kombinierter Beanspruchung daher sehr konservative Annahmen getroffen, die insbesondere im Hinblick auf die Materialermüdung des Stahls von geltenden Normenregelungen im Bauwesen abweichen und vergleichsweise unwirtschaftliche Ergebnisse liefern. In der vorliegenden Arbeit wurde der Einfluss des statischen Lastniveaus auf das Schädigungsverhalten und die Tragfähigkeit von ermüdungsbeanspruchten Befestigungen bei Stahlversagen systematisch untersucht. Hierzu erfolgten experimentelle Untersuchungen an drei verschiedenen Typen mechanischer Befestigungsmittel aus Kohlenstoffstahl, die durch unterschiedliche Kerbdetails gekennzeichnet sind. Aus den durchgeführten Untersuchungen geht hervor, dass der Einfluss des statischen Lastniveaus auf das Ermüdungsverhalten von Befestigungen von der Art des Befestigungsmittels abhängt und bei der Bemessung nicht generell vernachlässigt werden kann. In den Versuchen hat sich dennoch bestätigt, dass der Lastniveaueinfluss nach den vorliegenden Bemessungsansätzen überschätzt wird und je nach Befestigungsmittel zu unwirtschaftlichen Ergebnissen führen kann. Für die untersuchten Dübel und Kopfbolzen konnte ein ähnliches Ermüdungsverhalten wie bei Schraubenverbindungen im Stahlbau bzw. Kopfbolzendübeln im Verbundbau festgestellt werden. Dadurch ist es möglich, eine Bewertung der Ermüdungstragfähigkeit von Befestigungen auf der Basis des Nennspannungskonzepts vorzunehmen. Auf Grundlage der erzielten Erkenntnisse wird ein neues Bemessungskonzept zur Bestimmung des Ermüdungswiderstandes mit statischen Lastanteilen abgeleitet. Dieses erlaubt, die vorhandenen Tragfähigkeitsreserven von Befestigungen unter kombinierter Beanspruchung bei der Bemessung zu nutzen. Darauf basierend wird ein mehrstufiges Nachweiskonzept vorgestellt, das aus drei verschiedenen Bemessungsverfahren besteht, die einen zunehmenden Grad an Genauigkeit und Komplexität bei der Nachweisführung aufweisen. Dies führt zu einer effizienteren Auslegung von Befestigungen wie auch zu Potentialen bei der Bewertung der Restnutzungsdauer von bestehenden Anschlüssen und liefert damit einen wichtigen Beitrag zur Ressourceneinsparung im Bauwesen.Item Open Access Building optimization through a parametric design platform : using sensitivity analysis to improve a radial based algorithm performance(2021) Sakiyama, Nayara R. M.; Carlo, Joyce C.; Mazzaferro, Leonardo; Garrecht, HaraldPerformance-based design using computational and parametric optimization is an effective strategy to solve the multiobjective problems typical of building design. In this sense, this study investigates the developing process of parametric modeling and optimization of a naturally ventilated house located in a region with well-defined seasons. Its purpose is to improve its thermal comfort during the cooling period by maximizing Natural Ventilation Effectiveness (NVE) and diminishing annual building energy demand, namely Total Cooling Loads (TCL) and Total Heating Loads (THL). Following a structured workflow, divided into (i) model setting, (ii) Sensitivity Analyses (SA), and (iii) Multiobjective Optimization (MOO), the process is straightforwardly implemented through a 3D parametric modeling platform. After building set up, the input variables number is firstly reduced with SA, and the last step runs with an innovative model-based optimization algorithm (RBFOpt), particularly appropriate for time-intensive performance simulations. The impact of design variables on the three-performance metrics is comprehensively discussed, with a direct relationship between NVE and TCL. MOO results indicate a great potential for natural ventilation and heating energy savings for the residential building set as a reference, showing an improvement between 14-87% and 26-34% for NVE and THL, respectively. The approach meets the current environmental demands related to reducing energy consumption and CO2 emissions, which include passive design implementations, such as natural or hybrid ventilation. Moreover, the design solutions and building orientation, window-to-wall ratio, and envelope properties could be used as guidance in similar typologies and climates. Finally, the adopted framework configures a practical and replicable approach for studies aiming to develop high-performance buildings through MOO.