Abschlussarbeiten

Der Zement- und Betonsektor, der die Hälfte aller verwendeten Materialien verbraucht und ein Viertel aller Emissionen in der Branche verursacht, spielt eine entscheidende Rolle bei der Erfüllung des Pariser Abkommens und der Dekarbonisierung der Bauindustrie bis 2050. Dieses Ziel kann nur durch gemeinsames Handeln aller Beteiligten auf allen Ebenen, vom Zement über die Herstellung bis zum Bau, entlang der gesamten Wertschöpfungskette erreicht werden. Eine signifikante Verringerung des Betonverbrauchs in Bauelementen kann durch die Anwendung von Leichtbauprinzipien erzielt werden. Dabei entstehen filigrane, oft geometrisch komplexe Strukturen die mit Faserverbundfilamenten als Alternative zu herkömmlichen Stahlstäben bewehrt werden. Derzeit liegen nur experimentelle Ergebnisse dieser Systeme aus Zug- und Verbundversuchen vor. Um die Modellierung sowie die strukturelle Berechnung der komplex bewehrten Strukturen zu er[1]möglichen, ist es notwendig, die Modellierungsparameter zu ermitteln und einfache Simulationsmodelle herzuleiten. Digitale Modellierungstechniken, wie die Finite-Elemente-Analyse, bieten die Möglichkeit, das Verhalten der Faserverbundmaterialien unter verschiedenen Belastungsbedingungen zu simulieren und deren Interaktion mit dem umgebenden Beton zu untersuchen. Im Rahmen dieser Abschlussarbeit liegt der Fokus auf der numerischen Modellierung von Faserverbundsystemen in filigranen Betonstrukturen. Dabei sollen die mechanischen Eigenschaften der Faserverbundmaterialien sowie deren Verbundverhalten mit Beton untersucht werden. Schlussendlich sollen die Materialmodelle kalibriert und mit experimentellen Untersuchungen validiert werden. Als FE[1]Software wird mit dem Programm Abaqus gearbeitet. Eine ausreichende Zeit zur Einarbeitung wird gewährt.

Ansprechpartner:

Olga Miller M.Sc.
Tel: +49 (0)711 685 63794
E-Mail: olga.miller@ilek.uni-stuttgart.de

BSc/MSc Project

The bridge stock in the Trans-European Transport Network (TEN-T) is aging and it has been estimated that approximately 40-50% of the bridges in Germany, Netherlands and Denmark and Portugal will soon approach the end of service (older than 40 years). In addition, given the increased traffic demand, most bridges built before 1980 typically experience significantly stronger solicitations than the loads they were designed to withstand.

External post-tensioning can be used effectively to improve the serviceability performance of a bridge and to delay or prevent the onset of damage (e.g., cracking) [1]. Since typical post-tensioning increases flexural stiffness, it has been successfully employed to reduce in-service deflections and vibrations of short-span bridges [1]. Post-tensioning has been primarily implemented using unbonded tendons that run through the bridge cross-section and are anchored at the bridge ends. The tendons can be straight or draped using deviators. In either case, the tension force from the external cables is applied eccentrically to the neutral axis of the bridge cross-section. The resulting system of forces induces a bending moment that counteracts the effect of the external load. However, conventional external post-tensioning systems can only be effective against one loading condition, which is usually the permanent load. In scenarios where the live load is commensurate with the dead load and strict criteria for safety and serviceability apply, e.g., for high-speed railway bridges, conventional post-tensioning does not perform optimally.

Previous work has shown that structural adaptation can be employed to significantly improve structural capacity through stress homogenization by redirecting the force flow from critically stressed elements to lower-stressed elements [2]–[4]. In addition, adaptation can be employed to improve serviceability performance by reducing deflections and vibrations[5], [6]. Most bridges typically retain a significant reserve capacity [7] that could be unlocked through optimal retrofitting of control systems (e.g., sensors, actuators, and processing units) thus avoiding costly decommission and replacement by extending their service life.

External adaptive tensioning (EAT) systems can be retrofitted to existing bridges and employed for the design of new bridges [8]. A type of external adaptive post-tensioning system that is well-suited for retrofitting on different bridge types comprises cables deviated by variable-length compressive struts that are fixed below the bridge deck, as shown in Figure 1. Linear actuators adjust the length of the structs, which changes the tension in the cables allowing manipulation of the bending moment as the load changes. Simulations have been carried out on high-speed railway bridges modeled with simply supported steel-composite beams. Active control performed by the EAT system enables satisfying required vertical acceleration limits without the need to increase flexural stiffness by adding more material [8].

This work will investigate several bridge configurations and evaluate the potential of active control through different actuation strategies including EAT. This research project comprises two main tasks:

• Evaluation of the adaptation potential of beam, frame, truss, arch, suspension and cable-stayed bridges. This task involves modeling and simulation to evaluate how the structural capacity and serviceability performance can be improved through different actuation systems.
• Development of actuation strategies to extend the service life of existing and new bridges by mitigating the effect of heavy crossing to reduce the cyclic stress range.

For short- to medium-span highway and railway bridges, the objective is to reduce vibrations and stresses caused by heavy loading to extend the service life by mitigating fatigue effects. The potential of adaptation on the performance of lightweight (e.g., pedestrian), as well as stiffness-dominated bridges including long-span cable-stay and suspension configurations, will also be considered. For new bridges, the objective is to improve the structural performance by reducing significantly material mass requirements and in parallel increasing the span. 

Supervision

Dr. Eng. habil. Gennaro Senatore, gennaro.senatore@ilek.uni-stuttgart.de

Institute for Lightweight Structures and Conceptual Design (ILEK)

Supervision will be carried out in English.

Kontaktperson:
Dr.-Ing. Walter Haase
walter.haase@ilek.uni-stuttgart.de

Im Rahmen dieser hochaktuellen Abschlussarbeit soll das Potenzial elektrochemischer Verfahren zur nachhaltigen Zementherstellung untersucht werden. Der Fokus liegt auf der Konzeption und dem Bau eines funktionsfähigen Miniatur-Prototyps zur elektrochemischen Zementproduktion sowie auf der Analyse des Karbonatisierungsverhaltens der hergestellten Zemente. Das Thema adressiert eine zentrale Herausforderung auf dem Weg zu CO₂-armen Baustoffen der Zukunft. Ziel der Arbeit ist es, ein praktisches Verständnis für elektrochemisch hergestellten Zement zu entwickeln und dessen Karbonatisierungskinetik zu erforschen – ein entscheidender Faktor für die langfristige Leistungsfähigkeit und Umweltbilanz.

Fabricability and structural performance of the filigree concrete components reinforced with continuous tailor-placed basalt fibers.

Consuming half of all materials used and producing a quarter of all emissions in the industry, the cement and concrete sectors play a critical role in meeting the Paris Agreement and decarbonizing the construction industry by 2050. This goal can only be achieved through joint action by all stakeholders at all levels, from cement to construction, along the entire value chain. Measures to reduce concrete demand at the construction level and the implementation of circular economy principles are assessed as the most straightforward scenario with the shortest implementation time and highest efficiency.

Reduction of concrete consumption in structural elements can be achieved through the application of lightweight design principles. However, such filigree, usually geometrically complex structures require appropriate reinforcement strategies alternative to standard steel rebars. Among potential reinforcing materials, basalt fibers represent a great potential both technically and environmentally. They have higher strength than steel and are comparable to carbon and glass fibers, but with significantly less embodied energy. In addition, produced from basalt rock, they have a mineral base, enhancing recycling of concrete components at the end of their service life.

An open research question is the use of basalt fibers in filigree concrete structures that require their tailor placement along principle tensile trajectories. For this purpose, the fibers must be combined with an appropriate coating that provides rapid curing during application as well as protection from the alkaline environment of hydrated concrete. Thus, the objectives of the thesis include:

• investigation of fiber and coating formulations suitable for tailor place-ment, mechanical properties of fiber-coating compounds;
• experimental setup for tailored fiber placement;
• production of demonstration object to account for tailored fiber place-ment setup and prove fabrication related issues;
• experimental setup to account for alkali resistance of the tailored fiber composite reinforcement used in concrete construction;
• characterization of mechanical properties (exposed vs. non-exposed to alkali environment) to account for structural performance.

If you are interested, please apply to:
Dipl.-Arch. Daria Kovaleva daria.kovaleva@ilek.uni-stuttgart.de
David Nigl, M.Sc. david.nigl@ilek.uni-stuttgart.de

Contact persons:
Dr.Eng. habil. Gennaro Senatore (gennaro.senatore@ilek.uni-stuttgart.de)
Dr. ès sc. Arka P. Reksowardojo (arka.reksowardojo@ilek.uni-stuttgart.de)

The clear link between climate change and the environmental impact of the construction industry calls for innovative design approaches as well as alternative material solutions. Novel design strategies are emerging through the integration of advanced material research, computational design, and fabrication techniques. This higher level of integration allows materials that were previously considered as structurally insufficient, such as biomaterials, to be used in the context of built environment. By employing computer-aided shape optimization and form-finding, geometries that are most appropriate for given material properties can be obtained. In addition, 3D printing enables fabrication of complex geometries that are otherwise infeasible through conventional means.

Currently, large-scale 3D printing of Natural Fibre-Reinforced Polymers (NFRPs) has not yet been fully explored, especially in the use of continuous fibre filaments. From load-bearing point of view, the integration of continuous fibre within structural elements can be advantageous since it allows a contiguous distribution of forces. Conventional techniques for manufacturing continuous Fibre-reinforced polymers (FRPs) include several complex processes and steps, resulting in intense labour and energy expenditure. On the other hand, 3D printing of fibre filaments can produce complex geometries through the combination of fibre impregnation, deposition, and curing within a one-step process that can accommodate single or multi-material deposition.

In this project, a proof-of-concept prototype of 3D printed beam will be synthesized through topology optimization and then fabricated. To this end, the candidate will be expected to complete the following work packages: (1) literature review on biomaterials and 3D printed structures; (2) material characterization of 3D printed NFRP from existing empirical data and testing of new specimens; (3) topology optimization and modelling of the beam prototype (4) fabrication of 3D printed beam.

Note that thesis supervision, writing, and examination will be carried out in English.

Key requirements:
• Bachelor’s degree in civil engineering or architecture.
• Good knowledge of form-finding and finite element (FE) modelling.
• Notional knowledge or interest in structural optimization.
• Fluency in FE software (Abaqus/SOFiSTiK) and programming (Python/MATLAB).
• Experience and interest in 3D printing and/or biomaterials are an advantage.
• Proficiency in spoken and written English.

Contact:
Dr. ès sc. Arka P. Reksowardojo
Vanessa Costalonga, M.Sc.
✉ arka.reksowardojo@ilek.uni-stuttgart.de
✉ vanessa.costalonga@itke.uni-stuttgart.de

Earliest starting date:
01.08.2023

Contact person:

Dr.-Ing. Gennaro Senatore: gennaro.senatore@ilek.uni-stuttgart.de

Contact person:

Dr.-Ing. Gennaro Senatore: gennaro.senatore@ilek.uni-stuttgart.de

Investigation on CO₂ sequestration potential of lightweight concrete structures through long-term carbonation

Contact persons:
Dipl.-Arch. Daria Kovaleva          daria.kovaleva@ilek.uni-stuttgart.de
Maximilian Nistler, M.Sc.           maximilian.nistler@isw.uni-stuttgart.de