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High strain rate hardening of metallic cellular metamaterials
Nejc Novak, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek

Opis: Strain rate hardening caused by the changed deformation mode is a fascinating phenomenon in cellular metamaterials where the material’s stiffness and energy absorption capabilities increase as the strain rate increases. This unique behaviour is attributed to a combination of micro-inertia effects, base material’s strain rate hardening and inertia effects. At high strain rates, the metamaterial’s inertia influences its deformation response, which changes to shock mode. This work briefly presents the geometry and fabrication of different metallic metamaterials. Then, it evaluates their mechanical response at different strain rates, ranging from quasi-static to intermediate dynamic and shock, determined by experimental and computational investigation. The three deformation modes can be separated into two critical loading velocities, unique for each metamaterial, which are also presented and compared in this work for various metamaterials. The investigations show that the deformation mode change in metallic metamaterials depends on their porosity. The critical velocities separating the deformation modes decrease with increasing porosity, i.e., decreased density of the metamaterial results in reduced critical loading velocities. The shock deformation mode in cellular metamaterials is thus attainable at much lower loading velocities than in homogeneous (nonporous) materials.
Ključne besede: metamaterials, cellular structures, high strain rate, experimental testing, computational modelling, compression loading, mechanical properties
Objavljeno v DKUM: 22.05.2024; Ogledov: 155; Prenosov: 6
.pdf Celotno besedilo (3,42 MB)
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The cut method on hypergraphs for the Wiener index
Sandi Klavžar, Gašper Domen Romih, 2023, izvirni znanstveni članek

Opis: The cut method has been proved to be extremely useful in chemical graph theory. In this paper the cut method is extended to hypergraphs. More precisely, the method is developed for the Wiener index of ▫$k$▫-uniform partial cube-hypergraphs. The method is applied to cube-hypergraphs and hypertrees. Extensions of the method to hypergraphs arising in chemistry which are not necessary ▫$k$▫-uniform and/or not necessary linear are also developed.
Ključne besede: hypergraphs, Wiener index, cut method, partial cube-hypergraphs, hypertrees, phenylene, Clar structures
Objavljeno v DKUM: 11.04.2024; Ogledov: 188; Prenosov: 5
.pdf Celotno besedilo (318,42 KB)
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Numerical analysis of the racking behaviour of multi-storey timber-framed buildings considering load-bearing function of double-skin façade elements
Miroslav Premrov, Erika Kozem Šilih, 2023, izvirni znanstveni članek

Opis: The paper presents an innovative approach in the modelling of multi-storey timber-framed buildings, where double-skin façade elements (DSF) are additionally considered as load-bearing wall elements against a horizontal load impact. The mathematical model with a fictive diagonal element developed for timber-framed wall elements with classical oriented strand boards (OSB) or fibre–plaster sheathing boards (FPB) is upgraded for DSF elements. The diameter of the fictive diagonal is determined with either experimental results or numerically obtained results using the time-consuming FEM model with elastic spring elements, which simulates the bonding line between the timber frame and both glazing panes. In the second part of the study, the numerical analysis of a specially selected three-storey timber-framed building was performed using the developed mathematical model with fictive diagonal elements. Two alternative calculations were performed with the DSF elements as non-resisting and racking-resisting wall elements. It was demonstrated on the selected case that the racking resistance (R) of a building can essentially increase up to 35% if DSF elements are considered as resisting wall elements. As a secondary goal of the study, it is also important to point out that by using DSF elements as racking-resisting elements, the distortion in the first floor essentially decreased. It is demonstrated on the selected numerical example that this torsional influence decreased notably (by almost 18%) when the load-bearing DSF elements were used for seismic excitation in the X direction. Therefore, such an approach can open new perspectives in designing multi-storey timber-framed buildings with a more attractive and dynamic floor plan and structure.
Ključne besede: sustainability, timber, structures, multi-storey, numerical analysis, DSF, racking resistance
Objavljeno v DKUM: 19.03.2024; Ogledov: 185; Prenosov: 23
.pdf Celotno besedilo (4,93 MB)
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Development, fabrication and mechanical characterisation of auxetic bicycle handlebar grip
Nejc Novak, Vasja Plesec, Gregor Harih, Andrej Cupar, Jasmin Kaljun, Matej Vesenjak, 2023, izvirni znanstveni članek

Opis: The auxetic cellular structures are one of the most promising metamaterials for vibration damping and crash absorption applications. Therefore, their use in the bicycle handlebar grip was studied in this work. A preliminary computational design study was performed using various auxetic and non-auxetic geometries under four load cases, which can typically appear. The most representative geometries were then selected and fabricated using additive manufacturing. These geometries were then experimentally tested to validate the discrete and homogenised computational models. The homogenised computational model was then used to analyse the biomechanical behaviour of the handlebar grip. It was observed that handle grip made from auxetic cellular metamaterials reduce the high contact pressures, provide similar stability and hereby improve the handlebar ergonomics.
Ključne besede: auxetic cellular structures, computational simulations, experimental testing
Objavljeno v DKUM: 23.05.2023; Ogledov: 348; Prenosov: 40
.pdf Celotno besedilo (2,63 MB)

Simon Hudales, 2022, magistrsko delo

Opis: For the design of slender structures consisting of plates and tubes, such as supporting structures at cranes, buckling is beside stress and fatigue often the governing failure criteria. Stability analysis of such structures is usually performed using the GMNIA method according to DIN EN 1993. For this purpose, a suitable geometric equivalent imperfection must be applied to the structure. Buckling inherent shapes are determined for this purpose and scaled according to applicable safety concepts. Including imperfections in stability analysis can generally be relevant for the load-bearing behavior of a structure. Within this master thesis work, the influence of the initial geometric imperfection on stability behaviour is investigated. This study examines the influence, that imperfections imposed on members subjected to tensile stress have on stability behaviour. Tensile members of structures are identified and initial geometric imperfection is imposed on them in addition to critical members, that are subjected to compression stress. It is shown, that including imperfections on tensile members in stability analysis, has only a minor influence on stability behaviour and stiffness of the structure, both reducing it just slightly. Further on, investigation on boom model, that is supporting structure of the crawler crane, is made. Boom model consist of main chord members and diagonals connecting them. At the joint connection of boom and two diagonal members, one subjected to tension and one subjected to compression stress, appears area of high shear stresses. Influence of the direction, that imperfection is imposed on the diagonal member, and what is the influence on the stability behaviour and structural strength is presented in this work. Most severe case of the two chosen direction is pointed out and discussed.
Ključne besede: stability analysis, initial geometric imperfections, thin-walled structures, finite element method
Objavljeno v DKUM: 06.07.2022; Ogledov: 539; Prenosov: 53
.pdf Celotno besedilo (5,14 MB)

Retaining structure in demanding ground conditions: PK-16, road Hrastnik - Zidani Most : master's thesis
Aleksandr Sokolov, 2021, magistrsko delo

Opis: The master thesis presents the findings of the review of the design documentation of PGD plans for the PK-16 retaining structure, reconstruction of the G2-108 Hrastnik - Zidani Most road and deviation of the G1-5 Rimske Toplice - Zidani Most - Radeče road. The PK 16 retaining structure is foreseen between the Sava riverbed and the new road. The length of the retaining structure is substaintal (approx. 1140 m), the morphology of the terrain along the wall varies greatly. However, due to the erosion of the Sava River, it is estimated that the wall will need to be deep or corrosion protection should be constructed. Temporary security and work platforms based on the Sava River Basin (which is already impounded and quite deep in this part) will be required. The retaining structure is designed as a vertical cantilever wall that is on the underside rigidly fixed to the horizontal foundation plate. On the bulk of the structure, the foundation plate is supported by piles in two rows. The vertical wall at the top passes into a horizontal cantilever along which a corridor with a fringe runs. The controlling calculations were done employing a computational 2D model that takes into account the elastoplastic Mohr - Coulomb model for soil and the elastic model of concrete structures. The accompanying geotechnical calculations of the retaining structure in profiles P283 and P299 were compared with the analyses made in the design project to confirm the possibility of carrying out the proposed structures.
Ključne besede: civil engineering, geotechnical design, retaining structures, cantilever walls, piles
Objavljeno v DKUM: 13.10.2021; Ogledov: 975; Prenosov: 50
.pdf Celotno besedilo (2,99 MB)

Modeliranje in armiranje prekladnih elementov mostnih konstrukcij s programom Tekla Structures : diplomsko delo
David Tomaž, 2021, diplomsko delo

Opis: Diplomsko delo obravnava možnosti uporabe programa Tekla Structures, Rhino in Grasshopper pri modeliranju, armiranju in izdelavi armaturnih risb na realnih primerih prekladnih mostnih konstrukcij Viadukta Pesnice ter Mostu čez Savo v Krškem, ki je zahtevnejše oblike. V diplomskem delu je najprej predstavljen princip delovanja programov Tekla Structures, Rhino in Grasshoper, nato pa prikazan postopek modeliranja in armiranja ter izdelave armaturnih risb v programu Tekla Structures.
Ključne besede: modeliranje, armiranje, mostovi, Tekla Structures, Rhino, Grasshopper
Objavljeno v DKUM: 07.10.2021; Ogledov: 970; Prenosov: 127
.pdf Celotno besedilo (8,96 MB)

A three-dimensional static numerical model of a complex underground structure in high squeezing ground
Tina Marolt Čebašek, Jakob Likar, 2015, izvirni znanstveni članek

Opis: The present study assesses high squeezing ground confirmed by empirical and semi-empirical theories. High squeezing ground is often present in underground constructions at great depths, but it is hardly ever researched separately from light and fair squeezing ground. A three-dimensional, static numerical model is developed for a complex underground structure consisting of a shaft, a silo, and a mine roadway at great depth, which is certainly in high squeezing ground. Furthermore, a solution for the entire structure based on shotcrete with incorporated yielding elements is provided. The yielding elements, in general, absorb the strain energy by compressing at a relatively constant stress, but without rebounding. A three-dimensional, static numerical model of a support system with incorporated yielding elements is established in order to demonstrate that the presented forces are under control. Therefore, a failure of the lining is avoided because the stresses in the shotcrete lining are below its load-bearing capacity. It can be concluded that yielding elements incorporated in the shotcrete lining play an important role in the support solution in high squeezing ground.
Ključne besede: high squeezing ground, numerical model, underground structures, deformations, yielding support element
Objavljeno v DKUM: 14.06.2018; Ogledov: 1196; Prenosov: 204
.pdf Celotno besedilo (606,20 KB)
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Ground-sourced energy wells for heating and cooling of buildings
Heinz Brandl, Dietmar Adam, Roman Markiewicz, 2006, izvirni znanstveni članek

Opis: Energy wells are thermo-active elements for an economical extraction or storage of ground energy, similar to energy piles and other deep foundation elements also used as heat exchangers. Heating and/or cooling of buildings requires a primary and secondary thermo-active circuit, commonly connected by a heat pump. The paper gives several design aspects of energy wells which can be also used for the design of deep energy foundations. Thermal response tests have proved suitable for the in-situ determination of thermal ground properties required for an optimised design. Moreover, different systems of energy wells are discussed, and a comprehensive pilot research project is described.
Ključne besede: energy wells, energy foundations, geothermal geotechnics, geothermal heating/cooling, thermo-active structures, thermal ground properties, field testing
Objavljeno v DKUM: 17.05.2018; Ogledov: 1050; Prenosov: 124
.pdf Celotno besedilo (4,24 MB)
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The anchored pile wall optimization using NLP approach
Helena Vrecl-Kojc, 2005, izvirni znanstveni članek

Opis: The type of a retaining structure as well as the structure configuration mainly depends on geological conditions. If geological, urban and other data allow an alternative, the costs should also be considered as an important factor. In geotechnical practise, pile walls are especially used in excavations, in the erection of traffic facilities and in the sanitation of landslides. This paper is aimed at presenting economical differences between cantilever and anchoring pile walls and the impact of different parameters on costs. The optimization method, which uses mathematical programming, gives an optimal solution to geometry, self-manufacturing costs, and other characteristics of the structure in a uniform optimization process. This paper presents the optimization process using the nonlinear programming (NLP) approach for the anchored pile wall. The application presented only serves to confirm the effectiveness of the proposed optimization method. Therefore, the retaining structure is situated in homogeneous non-cohesive soil at three different soil friction angles of 35°, 30° and 25°. The generalized analytical method, the USA method, which was first introduced by Bowles [3], isused in the application. The analysis of the results shows the impact of parameters, the main controlling factors, configuration geometry and savings. The optimal results allowed from 18 up to 47 per cent savings compared to the cantilever pile wall depending on ground and structure input data and the excavation depth.
Ključne besede: civil engineering, optimum design, retaining structures, USA analytical method, nonlinear programming
Objavljeno v DKUM: 16.05.2018; Ogledov: 1373; Prenosov: 65
.pdf Celotno besedilo (216,45 KB)
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