Ojačavanje podnih konstrukcija CLT pločama - numerička studija

The purpose of this article is to provide an insight into the field of timber floor strengthening with cross-laminated timber (CLT) panels. A classic timber floor strengthened with CLT panels is therefore analysed according to the current building standards in the European Union, the Eurocodes. Seven different CLT panels, with thicknesses from 60 mm to 120 mm, are taken into consideration for the numerical study. Self-tapping screws with a diameter of 6 mm and length of 200 mm are used as shear connectors. The gamma method is used for calculating the effective bending stiffness. The design procedure is briefly presented, and the results for different configurations are compared.Cilj je ovog rada pokazati kako ojačati podne konstrukcije koristeći unakrsno laminirane drvene panele (CLT paneli). Kao predmet studije uzete su klasične drvene podne konstrukcije ojačane sa CLT panelima i uspoređene s Eurocode standardima, službenim graditeljskim standardom u EU-u. Sedam različitih tipova panela debljine od 60 do 120 mm su analizirani u numeričkoj studiji. Kao sredstvo sprezanja uzeti su samourezujući vijci promjera 6 mm i duljine 200 mm. Za proračun efektivne savojne krutosti korištena je gama metoda. U radu je kratko prikazana procedura dimenzioniranja te su uspoređeni rezultati različitih konfiguracija podnih konstrukcija

THE MIXED INTEGER NONLINEAR PROGRAMMING OPTIMIZATION OF BEAMS AND COLUMNS

Magistrsko delo obravnava optimizacijo nosilcev in stebrov iz armiranega betona, jekla in lepljenega lameliranega lesa. Za izbrane konstrukcije so bili izračunani optimalni (najnižji) materialni stroški in izbrane optimalne dimenzije prečnih prerezov ter trdnostni razredi posameznega materiala. Izračuni so bili izvedeni za različne razpone nosilcev, različne višine stebrov in različne koristne obtežbe. Rezultati so bili med seboj primerjani. Za optimizacijo, ki je bila izvedena z mešanim celoštevilskim nelinearnim programiranjem, so bili razviti in uporabljeni optimizacijski modeli omenjenih konstrukcij, zapisani v višjem algebrajskem jeziku GAMS.This Master thesis deals with the optimization of beams and columns made of reinforced concrete, steel and glued laminated timber. For selected structures the optimal (minimal) material costs, optimal cross section dimensions and optimal strength classes were calculated. The calculations were performed for different spans of beams, different heights of columns and for different live loads. The results were compared. For the optimization, which was performed by the Mixed Integer Nonlinear Programming approach, optimization models of the mentioned structures were developed and applied, modelled in GAMS, a high level language

DEVELOPMENT OF A NEW PROCEDURE FOR STRENGTHENING OF OLD TIMBER FLOORS

Leseni stropi se pogosto ojačujejo na način, da se na spodnjo stran stropnikov, ki lesene strope sestavljajo, prilepijo ali drugače pritrdijo kovinski ali polimerni trakovi. S tem postopkom se zakrije večji del površine, ki določa videz lesenega stropa, in posledično je prvobitni videz lesenega stropa izgubljen. Z razvojem področja steklenih in delno steklenih konstrukcij (kompozitov) ter z napredkom tehnologije proizvodnje stekla in s tem tudi kakovosti tega transparentnega materiala, pa se ponuja neobičajna možnost uporabe stekla tudi za ojačitve, npr. lesenih konstrukcij. Če bi za ojačitev lesenih stropov uporabili steklene elemente, bi v veliki meri ohranili prvobitni videz. Ta ideja odpira številna vprašanja, ki so predmet te doktorske disertacije. V disertaciji je v kontekstu leseno-steklenih konstrukcij obravnavan razvoj postopka za ojačitev starih lesenih stropov s steklenimi elementi v obliki trakov, v natezni coni upogibnega prereza, ki kot prvi korak že zajema uporabo plošč iz križno lepljenega lesa (CLT) v tlačni coni upogibnega prereza. Za zvezo CLT plošče in stropnika so bili upoštevani lesni vijaki, za stik steklenega traku in stropnika pa sta bila upoštevana lepljeni in točkovni (mehanski) stik, ki je bil razvit v sklopu priprave doktorske disertacije. Doktorska disertacija obsega strižne preizkuse lepljenih stikov steklo-les pri različnih vlažnostih lesa in različnih temperaturah. Potrjeno je bilo, da ima lepljeni stik steklo-les potencial za uporabo pri starih lesenih konstrukcijah, ki so lahko podvržene različnim okoljskim pogojem. S strižnimi preizkusi novega točkovnega stika steklo-les je bilo dokazano, da se lahko pod določenimi pogoji stekleni elementi povežejo z lesenimi elementi tudi lesnimi vijaki. Točkovno pritrjevanje steklenih elementov z lesnimi vijaki je neinvaziven, reverzibilen in za videz konstrukcije neškodljiv način. Razviti so bili tudi analitični izrazi za oceno nosilnosti in togosti novega točkovnega stika, vzporedno pa je bila opravljena še numerična analiza togosti točkovnega stika. Z numeričnim izračunom so bili ocenjeni faktorji napetosti v steklu v okolici točkovnega stika pri različnih obremenitvah, s pomočjo katerih se lahko tudi z analitičnim izračunom ocenijo napetosti v točkovno pritrjenem steklenem traku. Najpomembnejši del doktorske disertacije predstavljajo štiritočkovni upogibni preizkusi z novim postopkom ojačanih lesenih stropnikov. Uporabljeni so bili stari leseni stropniki iz dvorca na Zgornji Polskavi, ki so bili iz objekta odstranjeni zaradi številnih poškodb. Mehanske lastnosti lesenih stropnikov so bile določene na podlagi nateznih preizkusov lesenih vzorcev, izdelanih iz lesa uporabljenih starih lesenih stropnikov. Vzporedno so bili opravljeni analitični in numerični izračuni nosilnosti in togosti ojačanih stropnikov z obtežbo, enako obremenitvi pri štiročkovnem upogibnem preizkusu. Predstavljena je tudi parametrična analiza nosilnosti z novim postopkom ojačanih lesenih stropnikov, s pomočjo katerih so bili identificirani najpomembnejši parametri, ki vplivajo na nosilnost ojačanih lesenih stropnikov. Dokazan je bil prispevek steklenih trakov k upogibni togosti lesenih stropnikov. Pod določenimi pogoji lahko stekleni trak poveča tudi nosilnost. Za bolj učinkovitega se je izkazal prilepljen stekleni trak, a tudi s točkovnim stikom pritrjen oz. privit stekleni trak lahko prispeva k nosilnosti lesenega stropnika.Timber floors are often strengthened in such a way that metal or polymer strips are attached to the underside of its timber joists. This process blocks the surface view that determines the appearance of the timber floor and consequently the original architecture of the timber floor is compromised. With the development in the field of glass and partial glass structures (composite materials) and with the development of the quality of the production of glass, a transparent material, there is also the unconventional possibility of using glass for reinforcements, e.g. in timber structures. In the case of glass elements used to strengthen timber floors, the original appearance would largely be retained. The idea of using glass elements to strengthen timber floors raises many questions which are the subject of this dissertation. In the context of timber-glass composites, the dissertation deals with the development of a method for the strengthening of old timber floors with glass elements in the form of strips in the tensile zone of the cross section. As a first step of the reinforcement method, cross laminated timber panels (CLT) are already provided in the compression zone of the cross section. Self-tapping screws were considered for the connection of the CLT panel with the timber floor joist, while for the contact of the glass strip with the timber floor joist, adhesive bonding and point (mechanical) fastening were considered. The point (mechanical) fastening for the glass-timber connection was developed within the scope of this dissertation. The dissertation includes shear tests of timber-glass adhesive joints at different timber moisture contents and different temperatures. It was confirmed that the bonded timber-glass contact has the potential to be used for old timber structures which may be exposed to different environmental conditions. The shear tests of the new timber-glass point connection have shown that under certain conditions glass elements can also be connected to timber elements using self-tapping screws. The timber-glass point connection with self-tapping screws represents a non-invasive, reversible and optically inconspicuous connection of the two materials. Analytical expressions were also developed to evaluate the load-bearing capacity and stiffness of the new point connection, and a numerical analysis of the stiffness of the point connection was also carried out. The numerical analysis was also used to estimate the stress factors in the glass element around the point connection under various loads, which provides the possibility to estimate the glass stresses around the point connection by analytical calculation. The most important part of the dissertation are the four-point bending tests with the new procedure for strengthening old timber floors. Old timber floor joists from the Manor Zgornja Polskava were used, which were removed from the building due to severe damage. The mechanical properties of the timber floor joists were determined on the basis of tensile tests on timber samples taken from the old timber floor joists. In parallel, analytical and numerical calculations of the load-bearing capacity and stiffness of the strengthened timber floor joists were carried out, whereby the loading conditions were equal to the load in the four-point bending test. In addition, a parametric analysis of the new procedure for strengthening of old timber floors is presented, which was used to determine the most important parameters influencing the load-bearing capacity of the strengthened timber floor joists. Finally, the contribution of glass strips to the bending stiffness of the timber floor joists was demonstrated. Under certain conditions, glass strips can also increase the load-bearing capacity. The adhesively bonded glass strip was shown to be more effective, but the mechanically connected glass strip can also contribute to the load-bearing capacity of a timber floor joist under certain conditions

Nonlinear Semi-Numeric and Finite Element Analysis of Three-Point Bending Tests of Notched Polymer Fiber-Reinforced Concrete Prisms

A nonlinear semi-numeric and finite element analysis of three-point bending tests of notched polymer fiber-reinforced concrete prisms was performed. The computational and experimental results were compared in terms of the load-displacement behavior. The vertical midspan displacement and the crack mouth opening displacement results were considered. The nonlinear semi-numeric computational procedure involved the moment-curvature relation, calculated by considering the constitutive material law from the fib Model Code for Concrete Structures 2010, and considered a plastic hinge mechanism to simulate the cracked region behavior. Two sets of tensile mechanical properties were considered for the constitutive material law: back-calculated (by an inverse analysis) tensile strength properties from the experimental results, and tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010. Other mechanical properties were determined by additional compressive tests and standard relations for the dependency of various mechanical properties on the concrete compressive strength. The nonlinear finite element analysis incorporated the Menetrey-Willam material model to simulate the fiber-reinforced concrete behavior. The nonlinear semi-numeric analysis load-displacement results based on the back-calculated tensile strength properties relatively accurately matched with the experimental results, whereas the nonlinear semi-numeric analysis load-displacement results based on tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010 and the nonlinear finite element analysis load-displacement results showed certain shortcomings

Full-Scale Test and Load-Bearing Capacity Evaluation of Synthetic-Polymer-Fiber-Reinforced Concrete Tetrapods under Quasi-Static Loading

This paper studies the load-bearing capacity of various concrete tetrapods under quasi-static loading. The tetrapods were made of plain concrete and synthetic-polymer-fiber-reinforced concrete. Load tests of the tetrapods were performed. The maximum load-bearing capacity and the residual-load-bearing capacity of the tetrapods (the load-bearing capacity after the first crack or at different crack widths) were evaluated. The strength and residual-strength values were back-calculated from the load-bearing capacities, and compared with available data from the literature. The specimens with and without fibers achieved similar maximum load-bearing capacities, with cracks occurring at identical locations. However, the differences in residual-load-bearing capacity were more significant. The synthetic-polymer-fiber-reinforced concrete tetrapods exhibited relatively high residual-load-bearing capacities, even at higher displacements and crack widths. Two different calculation-procedures were used for the load-bearing-capacity evaluation. A load-displacement calculation based on the moment-versus-curvature relation and the plastic-hinge approach was performed, and additionally proved the applicability of the employed calculation-procedures for the concrete tetrapod load-bearing-capacity evaluation

Full-Scale Test and Load-Bearing Capacity Evaluation of Synthetic-Polymer-Fiber-Reinforced Concrete Tetrapods under Quasi-Static Loading

This paper studies the load-bearing capacity of various concrete tetrapods under quasi-static loading. The tetrapods were made of plain concrete and synthetic-polymer-fiber-reinforced concrete. Load tests of the tetrapods were performed. The maximum load-bearing capacity and the residual-load-bearing capacity of the tetrapods (the load-bearing capacity after the first crack or at different crack widths) were evaluated. The strength and residual-strength values were back-calculated from the load-bearing capacities, and compared with available data from the literature. The specimens with and without fibers achieved similar maximum load-bearing capacities, with cracks occurring at identical locations. However, the differences in residual-load-bearing capacity were more significant. The synthetic-polymer-fiber-reinforced concrete tetrapods exhibited relatively high residual-load-bearing capacities, even at higher displacements and crack widths. Two different calculation-procedures were used for the load-bearing-capacity evaluation. A load-displacement calculation based on the moment-versus-curvature relation and the plastic-hinge approach was performed, and additionally proved the applicability of the employed calculation-procedures for the concrete tetrapod load-bearing-capacity evaluation