Browsing by Author "Markou, Athanasios A."

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    3D dataset of a twisted bending-active beam element digitized using structure-from-motion photogrammetry
    (Elsevier, 2024-06) Janiszewski, Mateusz; Elmas, Serenay; Markou, Athanasios A.; Jaaranen, Joonas; Filz, Günther H.; Department of Civil Engineering; Department of Architecture; Mineral Based Materials and Mechanics; Structures – Structural Engineering, Mechanics and Computation
    The current work presents the generation of a comprehensive spatial dataset of a lightweight beam element composed of four twisted plywood strips, achieved through the application of Structure-from-Motion (SfM) - Multi-view Stereo (MVS) photogrammetry techniques in controlled laboratory conditions. The data collection process was meticulously conducted to ensure accuracy and precision, employing scale bars of varying lengths. The captured images were then processed using photogrammetric software, leading to the creation of point clouds, meshes, and texture files. These data files represent the 3D model of the beam at different mesh sizes (raw, high-poly, medium-poly, and low-poly), adding a high level of detail to the 3D visualization. The dataset holds significant reuse potential and offers essential resources for further studies in numerical modeling, simulations of complex structures, and training machine learning algorithms. This data can also serve as validation sets for emerging photogrammetry methods and form-finding techniques, especially ones involving large deformations and geometric nonlinearities, particularly within the structural engineering field.
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    Experimental dataset of U-folded falling chain under various openings with high-speed imaging
    (Elsevier, 2023-02) Markou, Athanasios A.; Baroudi, Djebar; Cheng, Qiang; Bordbar, Hadi; Department of Civil Engineering; Department of Mechanical Engineering; Structures – Structural Engineering, Mechanics and Computation; Energy Conversion and Systems; Performance in Building Design and Construction
    A folded chain hanged by its two ends in U-shape at the same level with an opening, distance, between its two tips is known as U-folded chain, as studied in Markou et al. (2023). When one of the tips is fixed and the other one is released, the free tip of the U-folded falling chain accelerates faster than gravity, due to momentum conservation. This counterintuitive fact has long excited mechanicians around the globe. In the current paper we present a group of datasets (tip's coordinate timeseries), comprising three different subsets of this variable-mass dynamical system. A series of experiments of a U-folded falling chain of length 1.51m with total mass 31 gm, have been recorded with a high-speed imaging (2000 fps) (Markou et al., 2023). The distance between the tips of the chain (opening) varies throughout the experimental session series: (i) 0.045m, (ii) 0.087m and (iii) 0.128m. Three timeseries of the tip's coordinates (x,y) have been extracted using an edge detector based method, from the recorded high-speed videos.(c) 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
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    Geometrically nonlinear behaviour of actively twisted and bent plywood
    (Elsevier BV, 2024-03-01) Elmas, Serenay; Jaaranen, Joonas; Markou, Athanasios A.; Filz, Günther H.; Koponen, Simo; Department of Civil Engineering; Department of Architecture; Structures – Structural Engineering, Mechanics and Computation; UPM
    The current work aims to investigate the geometrically nonlinear behaviour of flexible plywood strips that undergo large displacements during the formation process of a structural element. Such deformations allow bending-active structures to reach curved geometries from initially planar elements. As our literature review points out, firstly, twist for plywood materials is not well studied, and secondly, the detailed determination of the stress state after the formation process of such structures, is usually oversimplified or even ignored. To this end, a finite element model using laminated shell theory is employed and calibrated against experimental data retrieved from physical prototypes, by paying particular attention in the accurate tuning of its boundary conditions. Furthermore, destructive tensile tests of twisted strips were implemented and their ultimate strength was compared with the numerical model. Our aim is to explore the material's stress state during the strip's 90°twist coupled with bending in two different directions, which is crucial for understanding the strip's further behaviour as a structural element. In addition, we conduct parametric studies to showcase the non-negligible impact of geometric aspects on stress distribution along the strip. The results show that the utilisation ratios, using the Tsai–Hill failure criterion in terms of strength, for the case of the constructed beam element, are quite uniform throughout the strip and below 50%, apart from local stress concentrations. Finally, the parametric studies highlight the need to comprehend the material response to inform geometry within a structurally sound environment in order to unlock new possibilities for using thin plywood strips in lightweight structural and architectural applications, as demonstrated by the built beam elements.
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    The structural geometry of a beam element from 4 torqued strips
    (2022-07-08) Filz, Günther H.; Elmas, Serenay; Markou, Athanasios A.; Department of Civil Engineering; Department of Architecture; Cruz, Paulo J.S.; Hvejsel, Marie Frier; Structures – Structural Engineering, Mechanics and Computation
    When assembling a tube from 4 identical, thin-walled, flexible, rectangular strips, which are hinge-joined along their longitudinal edges, a hollow, square cross-section is generated. One option for restraining the tube’s 1-DOF-mechanism around its longitudinal axis is to cross-wisely connect its ends at a common seamline. This procedure causes a twist of 90° and sideward shifts of each of the four strips. We provide a description and comparison of the structural geometry of such beam elements. Our investigations are based on physical prototypes, photogrammetric reconstruction, and computational simulations. The beam’s geometrical stiffness, paralleled with its ease of fabrication and assembly opens new avenues for the design of lightweight structures, firstly used in the realization of the kinematic Zero Gravity pavilion at Aalto University.
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    Unfolding the dynamics of free-falling folded chain : Experiments and simulations
    (Elsevier Ltd, 2023-01) Markou, Athanasios A.; Baroudi, Djebar; Cheng, Qiang; Bordbar, Hadi; Department of Civil Engineering; Department of Mechanical Engineering; Structures – Structural Engineering, Mechanics and Computation; Mineral Based Materials and Mechanics; Energy Conversion and Systems
    Contrary to educated intuition, the tip of a free-falling U-folded chain accelerates faster than gravity without violating the Newtonian laws. In the current work, we study the dynamics of a free-falling U-folded chain experimentally as well as numerically. To this end, high-speed imaging (up to 10000 fps) is used to capture the chain's falling tip by using different openings between the two tips of the chain. Thanks to high-speed digital imaging, the detailed geometry of the dynamic unfolding is captured. The post-processing of captured images has provided detailed quantitative temporal data for displacement, velocity, and acceleration of the falling tip of the chain. The experimental observations have revealed the various phases of dynamics of the falling U-folded chain, including unfolding, whipping, and rebounding phases for the first time. Furthermore, a Henky-type model is developed to capture the associated phenomena related to these phases, such as rebound effect, whip effect, local buckling, and transverse wave propagation. The model that includes nonlinear elastic, dissipative and bilateral gap-contact features, could successfully capture the experimentally observed phases and phenomena of the unfolding dynamics qualitatively.