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Aqueous Supercapacitors Based on Polymer-Biomass Composites
(2026) Zalem, Yohan
The development of sustainable aqueous supercapacitors requires the integration of high-performance conductive materials and abundant, environmentally friendly resources. This thesis investigates the electrochemical performance of composite electrodes comprising of conjugated polymers and lignosulfonate, a low-cost biomass derivative theoretically capable of providing additive pseudocapacitance through quinone-based reversible redox reactions. A comprehensive comparative analysis was conducted between established p-type polymers (PEDOT:F and PEDOT:PSS) and a novel, ultra-highly conductive n-type polymer, poly(benzodifurandione) (PBFDO). The active materials were deposited onto plasma-treated carbon paper substrates via a controlled sequential drop-casting method and evaluated in symmetrical two electrode Swagelok cells utilizing an aqueous perchloric acid electrolyte. Baseline electrochemical characterization via Cyclic Voltammetry (CV), Galvanos tatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) revealed that pristine PBFDO vastly outperformed both PEDOT derivatives. Eval uated at a low comparative current density of 0.25 A/g, PBFDO exhibited superior specific capacitance, exceptional structural resilience, and minimal Equivalent Series Resistance (ESR). Contrary to the central hypothesis, the incorporation of unmodified lignosulfonate severely degraded the performance of all tested polymers. Rather than acting as a synergistic redox contributor, the water-soluble and electrically insulating ligno sulfonate acted as an electrochemically inactive dead weight. While the p-type PEDOT composites suffered catastrophic electrochemical failure at a 1:1 polymer to-lignin mass ratio, the self-doped n-type PBFDO matrix demonstrated remarkable structural resilience. Although the specific capacitance of PBFDO systematically declined as the lignin concentration increased across 3:1, 1:1, and 1:3 mass ratios, it maintained its fundamental charge-storage mechanisms without the massive internal resistance spikes observed in the p-type cells. Ultimately, while highlighting the lim itations of physically blending raw lignosulfonate in aqueous electrolytes, this study unequivocally establishes the novel n-type PBFDO network as a premier, highly robust conjugated polymer for next-generation energy storage applications
Steel-Timber Composite Beams as an Alternative to Conventional Steel and Glulam - A Structural and Sustainability Assessment
(2026) Karydas , Dimitros Christos; Mohsen, Rashid
Steel and timber can be combined into hybrid structural elements known as steel timber composite (STC) beams, offering improved structural performance while reducing embodied carbon and cost compared to conventional alternatives. Despite their potential, no dedicated Eurocode provisions currently exist for STC beam de sign, limiting their adoption in practice and motivating the need for further research. This study investigates two STC configurations: STC-1, consisting of a steel HEA section with a glulam element positioned above the top flange, and STC-2, a glu lam beam reinforced with a steel plate on its bottom surface. Both configurations are designed using Newmark’s partial-interaction theory and optimized through a parameter sweep in MATLAB, in which Life Cycle Assessment(LCA) and Life Cy cle Cost (LCC) analyses are performed on the candidate configurations to obtain their CO2 emission and cost performance, with a Marginal Abatement Cost (MAC) framework subsequently applied as the selection criterion. The optimized STC con figurations are then compared against pure steel and pure glulam reference beams. LCA and LCC analyses are conducted across span lengths ranging from 3 m to 12 m, with nonlinear finite element simulations in Abaqus being performed for two representative spans of 7 m and 12 m under office and shopping mall load cases. Results show that STC beams can offer environmental and economic advantages beyond a threshold span length, with STC-1 achieving CO2 reductions of up to 20% relative to the steel reference beyond approximately 5 m, while STC-2 reduces cost up to 30% compared to the glulam reference beyond approximately 9 m. Finite el ement analysis confirms that both configurations exhibit ductile behavior governed by steel yielding, with failure modes and load-displacement responses varying be tween configurations and span lengths. These findings demonstrate that Newmark’s partial-interaction theory provides a viable design basis for STC beams in the ab sence of dedicated Eurocodes.
Effect of Bottom Flange Bracing on Crane Runway Girders - A Parametric Study on Ultimate Capacity Using Finite Element Analysis
(2026) Karlsson, Andreas; Tengberg, Kajsa
Crane runway girders in heavy industry carry large vertical and horizontal loads, placing significant demands on structural stability. While bracing of the top flange to prevent lateral-torsional buckling is well established, guidance on bottom flange bracing is inconsistent: the American Institute of Steel Construction (AISC) has reduced its previous requirement to a recommendation and Eurocode provides no explicit guidance on the matter. This study investigates the effect of bottom flange bracing on crane runway girders through a parametric finite element study in Abaqus, comparing the ultimate load capacity, quantified by the load proportionality factor (LPF), and lateral displacement of the bottom flange between girders braced at both flanges and girders with top flange bracing only. A range of web heights, bottom flange widths, and geometric imperfection amplitudes were considered. The model was verified against analytical hand calculations based on Eurocode, and the results were compared to AISC provisions for web sidesway buckling. The results show no significant capacity gain between the configurations, with a max imum ∆LPF gain of approximately 5-6%. The largest improvements are observed for intermediate web heights, and bottom flange widths, where bottom flange re straint allows for a more even stress distribution over the web. For larger geometric imperfection amplitudes, bracing the bottom flange can reduce capacity due to a self-straightening behavior that restraint prevents. The AISC comparison shows a consistent pattern, where narrower bottom flanges and lower web heights are more susceptible. Based on these findings, no strong case is found for introducing manda tory bottom flange bracing requirements in Eurocode for the geometries and load cases investigated. Rather than mandatory bracing requirements, a more appropri ate approach may be to control the bottom flange behavior through serviceability deflection limits, though further investigation is needed into how the lateral deflec tion of the bottom flange can be analytically determined, as this is dependent on cross sectional geometry.
A Hybrid Office Tower- ULS and SLS Dynamic Wind Study A Study of Parameters Affecting Different Wind Response Modes and Dynamic Performance of Tall Buildings
(2026) Hu, Bingjie; Kucins, Krisjanis
This thesis investigates the dynamic response of tall timber–concrete hybrid office build ings subjected to wind-induced vibrations, with a focus on occupant comfort according to ISO 10137:2008. It evaluates how different structural configurations influence the along-wind, across-wind, torsional, and combined responses of a high-rise building. A parametric study was carried out, varying core thickness, bracing system, aspect ratio, and added mass. Finite element models were developed and linked to a parametric workflow usingGrasshop per and Python. The results show that the along-wind response governs all configura tions, while the relative importance of across-wind and torsional responses varies with the structural strategy. However, considering only the along-wind response is not suf ficient for investigated configurations, and all three response modes should be assessed together. Serviceability in terms of occupant comfort governed both structural configuration and height. While the ultimate limit state was analysed, it was not governing for all studied configurations. Wind-induced accelerations were most effectively reduced by increas ing stiffness through diagonal bracing or a thicker core. Changes in aspect ratio signifi cantly reduced accelerations without additional material, indicating that early floor plan optimisation can be effective. However, with increasing height, timber–concrete hy brid structures become less material-efficient, requiring large concrete cores and added mass to meet serviceability criteria. The most efficient configurations were those up to 20 storeys. Overall, the thesis highlights the importance of considering all three response modes early in the design of tall timber–concrete hybrid buildings, as structural configuration strongly influences wind-induced vibration performance.
Elastic Rotational Stiffness of an Embedded Steel Plate-Timber Connection A Simplified Solution, Based on an Analytical Study Verified by Numerical Modeling
(2026) Gustafsson, Viktor; Katergi, Karam
Connections are among the most complex elements to analyze and design within struc tural engineering. They consist of multiple interacting components, involve intricate load-transfer mechanisms, and exhibit nonlinear behavior that is difficult to capture us ing simple assumptions. Although numerical modeling can be employed to evaluate connection behavior and stiffness, it is often computationally demanding and requires careful verification and interpretation. Consequently, connections are frequently idealized in the design phase as either perfectly pinned or fully fixed, and in some cases, assigned an intermediate stiffness. While such simplifications may be acceptable for simple structural systems, they offer limited insight into the governing parameters that influence connection stiff ness. These assumptions restrict the ability to optimize connection design and may be insufficient for structures with demanding performance requirements, such as high-rise hybrid buildings. The objective of this Master’s thesis is to develop a realistic analytical model for the internal parts of a steel-timber connection and the total rotational stiffness in the elastic state. The study considers an embedded steel plate connection, which is widely used due to its aesthetic appeal and ease of on-site installation. To achieve this objective, load paths and structural models are identified for internal parts in connection. By summing the resulting elastic deformations of each part, the total deformation and rotational response are obtained. The analytical results are sub sequently validated and calibrated against numerical simulations, including a 3D solid model and a 2D beammodel. Basedonthisprocess, asimplifiedandverifiedexpression for estimating the rotational stiffness of the embedded steel plate connection is derived. Keywords: embedded steel plate connections, slotted in steel plate-timber connection, elastic rotational stiffness, timber-concrete connection, connection rigidity.