Дисертації з теми "Concrete Structures-Shear and Torsion"
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Puurula, Arto. "Assessment of prestressed concrete bridges loaded in combined shear, torsion and bending /." Luleå, 2004. http://epubl.luth.se/1402-1757/2004/43.
Повний текст джерелаAlnuaimi, Ali Said Mohammed. "Direct design of reinforced and partially prestressed concrete beams for combined torsion, bending and shear." Thesis, Connect to e-thesis, 1999. http://theses.gla.ac.uk/652/.
Повний текст джерелаShaarbaf, Ihsan Ali Saib. "Three-dimensional non-linear finite element analysis of reinforced concrete beams in torsion : reinforced concrete members under torsion and bending are analysed up to failure : a non-linear concrete model for general states of stress including compressive strength degradation due to cracking is described." Thesis, University of Bradford, 1990. http://hdl.handle.net/10454/3576.
Повний текст джерелаPham, Keimann, and Jesse Olsson. "Bestämning av skjuvhållfasthet med vridprovning för pågjutna betongkonstruktioner." Thesis, KTH, Byggteknik och design, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-136826.
Повний текст джерелаDamages and wear on concrete bridges are due to de-icing salt or salt water, reinforcement corrosion and repeated freeze-thaw cycles in combination with increasing traffic loads. The most common repair operation for these types of damages is to remove the deteriorated concrete and replace it with a new concrete overlay. To evaluate how well a bonded concrete overlay is, the bond strength between the new and old concrete has to be determined. The most widely used method for this purpose is the so-called pull off test to determine the tensile bond strength. In practice however the shear bond strength is of greater interest and is therefore approximated on the basis of tensile bond strength, but with a torsion test the shear bond strength can be directly determined. The purpose of this study is to investigate the reliability of the torsion test to determine the shear bond strength in a more direct and accurate manner. The thesis examines the reliability of the torsion test to determine the shear bond strength with the pull off test as a reference. The study includes eight parallel tests of pull off and torsion tests where the lowest measured shear bond strength is compared with the calculated design value of shear bond strength according to EC2. The work is done in connection with the Spårväg city project at Sergels torg, Stockholm, in collaboration with the Traffic Administration Office in Stockholm and CBI, the Swedish Cement and Concrete Research Institute. The results of the tests showed that the failures in the interface between new and old concrete, which are of interest, were more common for pull off tests than torsion tests where only two of the eight test samples showed failure in the interface. The wide scatter of the measured values is a consequence of the low number of failures in the interface. The mean value of the tensile bond strength was 1,43 MPa, which indicates good bond strength. The shear bond strength however made with torsion tests show a mean value of only 1,61 MPa. Lower than the expected value of about twice the tensile bond strength of 2,86 MPa. Interestingly, the lowest measured value of the shear bond strength of 0,83 MPa was unusually low, but still higher than the calculated design value of shear bond strength of 0.59 MPa according to EC2. The study has shown that torsion test is a difficult method for determining the shear strength of the bond between the new and old concrete. The reason for this is mainly due to three factors, the low number of tests, the large scatter of values, and the difficulty to interpret failures of the test samples. Despite this the torsion test seems to be a future method for structural engineers and contractors as a tool to determine shear strength for repaired concrete structures in general and not only the shear bond strength.
Bairán, García Jesús Miguel. "A non-linear coupled model for the analysis of reinforced concrete sections under bending, shear, torsion and axial forces." Doctoral thesis, Universitat Politècnica de Catalunya, 2005. http://hdl.handle.net/10803/6177.
Повний текст джерелаEl objetivo principal de esta tesis es generalizar el análisis de secciones de hormigón armado mediante fibras, de forma que se pueda reproducir la res-puesta no-lineal acoplada frente a esfuerzos normales y tangenciales bajo solicitaciones tridimensionales generales. De igual forma, se pretende obtener, para los esfuerzos cortantes y torsión, la misma capacidad de representación de geometrías y combinación de materiales que ofrecen los modelos de fibras para esfuerzos de flexo-compresión.
La primera problemática estriba en representar adecuadamente la cinemática de la sección transversal. Con la excepción de las deformaciones normales contenidas en el plano de la sección, no existe una teoría cinemática que a priori pueda dar la distribución del resto de deformaciones o tensiones en la sección, sin dejar de satisfacer las condiciones de equilibrio interno o continuidad entre las fibras que componen la misma.
Por otra parte, para materiales anisótropos, como el hormigón fisurado, en general todos los esfuerzos internos pueden estar acoplados. Además, es preciso considerar la distorsión de la sección transversal para satisfacer el equilibrio entre fibras.
El problema se aborda de forma general, considerando una sección de forma y materiales cualesquiera. Se parte del problema diferencial de equilibrio de un sólido con el que se ha podido deducir un sistema de equilibrio entre fibras (equilibrio a nivel sección). Se puede demostrar que éste es complementario al problema estándar de vigas. El sistema complementario permite recuperar información tridimensional que normalmente se pierde al resolver un problema de vigas.
Posteriormente, se propone una solución interna del problema complementario, en la que el alabeo y la distorsión de la sección quedan expresados como una función de las deformaciones generalizadas de una viga: deformaciones axil y cortantes, curvaturas de flexión y torsión. No son necesarios grados de libertad adicionales a nivel estructura ni hipótesis a-priori sobre la forma de los campos de deformación o tensión interna.
A partir de la formulación teórica, se desarrolla un modelo de elementos finitos plano de la sección transversal. El modelo está preparado para servir como respuesta constitutiva de cualquier tipo de elemento viga en sus puntos de integración. %Se evita así la necesidad de realizar un modelo de elementos sólidos de toda la barra para estudiar la respuesta frente a una combinación general de esfuerzos normales y tangenciales.
Se implementan una serie de modelos constitutivos para distintos materiales. En particular, se implementa un modelo constitutivo triaxial para hormigón fisurado, considerando la anisotropía inducida por la fisuración e incluyendo la superficie de rotura según un criterio multiaxial.
La formulación seccional es validada mediante varios casos de estudio teóricos y experimentales. La respuesta no-lineal acoplada bajo diversas combinaciones de esfuerzos normales y tangenciales es reproducida con precisión, lo cual queda patente tanto en las curvas esfuerzo-deformación obtenidas como en las matrices de rigidez seccionales.
Finalmente, se recopilan las conclusiones derivadas de la presente investigación y se
ofren recomendaciones para futuros trabajos.
Most RC structures are subjected to combined normal and tangential forces, such as bending, axial load, shear and torsion. Concrete cracking, steel yielding and other material nonlinearities produce an anisotropic sectional response that results in a coupling between the effects of normal and shear forces, i.e. normal force or bending moments may produce shear strains and vice versa. Although this interaction is sometimes taken into account, in a simplified manner, in the design of RC structures, a deep analysis of the coupling effects of RC sections using fiber models has not yet been made for arbitrary shape sections under general 3D loading.
The main objective of this thesis is to generalize the fiber-like sectional analysis of reinforced concrete elements, to make it capable of considering the coupled non-linear response under tangential and normal internal forces, from a general 3D loading.
Similarly, it is desired to obtain, for torque and shear forces, the same capacity and versatility in reproducing complex geometry and materials combination that fiber-like sectional representations offers for bending and stretching.
The first problematic lies in finding a proper representation of the section's kinematics under such general loading. Except for in-plane normal strains, there is no single kinematical theory capable of a-priori representing the correct distribution of the others strains or stresses satisfying, at the same time, inter-fiber equilibrium and continuity. On the other hand, for rather anisotropic materials, such as cracked concrete, all internal forces are, in general, coupled. It is also required that distortion is allowed for the section's kinematics in order to guarantee satisfaction of internal equilibrium.
The problem is dealt in a general form considering arbitrary shaped sections and any material behaviour. Starting from the differential equilibrium of a solid, an inter-fiber equilibrium system (equilibrium at the sectional level) was deduced. This system, which is complementary to the standard equilibrium problem of a beam-column, allows to recuperate information of the three-dimensional problem that is generally lost when solving a beam problem.
Further, a solution of the equilibrium at the sectional level is proposed in which the section's warping and distortion are posed as a function of the generalized beam-column strains (axial and shear strains, bending and torsion curvatures). No additional degrees of freedom are required at the structural level nor a-priori hypotheses on the distribution of the internal strains or stresses.
After the theoretical formulation, a planar finite element model for cross-sectional analysis is developed. The model can be used as a constitutive law for general beam column elements at their integration points.
A series of constitutive models have been implemented for several materials. In particular, a triaxial constitutive model for cracked concrete is implemented considering crackinduced anisotropy and a multiaxial failure criterion.
The sectional formulation is validated by means of various theoretical and experimental case studies. Non-linear coupled response under normal and tangential internal forces is reproduced with accuracy, as can be seen both in the predicted internal force-strain curves and in the sectional stiffness matrixes.
Finally, the conclusions drawn from the current research are summarized and
recomendations for future works are given.
Grosser, Philipp R. [Verfasser], and Rolf [Akademischer Betreuer] Eligehausen. "Load-bearing behavior and design of anchorages subjected to shear and torsion loading in uncracked concrete / Philipp R. Grosser. Betreuer: Rolf Eligehausen." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2012. http://d-nb.info/1028801254/34.
Повний текст джерелаCapdevielle, Sophie. "Introduction du gauchissement dans les éléments finis multifibres pour la modélisation non linéaire des structures en béton armé." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI109/document.
Повний текст джерелаThe present work is dedicated to the numerical modeling of structures using multifiber beam elements. This numerical method was proved to be efficient to simulate the behavior of slender structural elements subject to normal stresses. However, the response of the model for shear-dominating stresses lacks of accuracy. This problem is addressed by introducing warping in the kinematics of multibfiber beam elements. A new multifiber element is developed in two steps. Torsional warping is first introduced in the deformations of an arbitrary-shaped composite cross section. The resulting warping profiles are validated by comparison with the axial displacements obtained by three-dimensional modeling of beams in torsion. After implementation of the warping kinematics in a Timoshenko multifiber beam element, the formulation is validated against the experimental behavior of beams subject to pure torsion. The material is modeled by a 3D damage law, and warping is updated throughout the computations to account for damage evolution. A comparison of torque–twist curves predicted with enhanced and classical beam elements to experimental curves highlights the importance of including warping in the model. The second step consists in formulating an element with additional warping degrees of freedom, accounting for the warping deformations due to both transverse shear and torsion. This element is validated using an analytical model for a beam subject to transverse shear. Then the linear elastic behavior of a beam subject to both shear and torsion is successfully compared to the results of a 3D simulation. The complete formulation is coupled to damage through an implicit soulution procedure for the beam and the warping degrees of freedom. The enhanced method is eventually used to compute the behavior of a full structure subject to a seismic loading
Nádvorník, Ondřej. "Návrh mostní konstrukce na rychlostní komunikaci." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-226420.
Повний текст джерелаEl-, Shihy A. M. "Unwelded shear connectors in composite steel and concrete structures." Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374861.
Повний текст джерелаIshtewi, Ahmad M. "Shear Capacity of Fiber-Reinforced Concrete Under Pure Shear." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1354725447.
Повний текст джерелаLindwall, Caroline, and Jonas Wester. "Modelling Lateral Stability of Prefabricated Concrete Structures." Thesis, KTH, Betongbyggnad, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188586.
Повний текст джерелаVid stabilitetsberäkningar av prefabricerade betongstommar med hjälp av FEM-verktyg ställs krav på kunskap om hur elementen förhåller sig till varandra. Detta arbete berör hur fogar mellan byggnadselement påverkar modellering av prefabricerade betongstommar med avgränsning till fogar mellan håldäckselement och mellan solida väggelement. Arbetet berör även en studie i hur ett bjälklags egenskaper kan justeras så att fogarnas effekt kan tillvaratas utan att modellera varje enskilt håldäckselement. Arbetet inleddes med att utböjningen analyserades hos 10 st ihopskarvade håldäckselement, lastade i dess plan likt en hög balk, i en FE-modell skapad i programmet Robot™, från Autodesk®. Fogarna mellan håldäcken modellerades som antingen rigida eller elastiska och håldäckens tvärsnittsgeometri och längd varierades under testet. Den linjära styvheten mellan håldäcken togs från litteraturen som 0.05 (GN/m)/m. Resultatet visade att ändrad tvärsnittsgeometri gav större skillnader för deformationen än varierad längd på håldäcken. Håldäckens skjuvmodul justerades sedan i dess plan för de rigida testen tills dess att de uppnådde samma utböjning som de elastiska. Resultatet visade att skjuvmodulen behövdes reduceras med en faktor 0.1, i medeltal för de olika tvärsnittsgeometrierna och håldäckslängderna. Utefter geometrin på en fog med förtagningar mellan prefabricerade väggar togs en beräkningsmodell fram för den linjärelastiska styvheten i väggfogarna. Resultatet blev en styvhet på 1.86 (GN/m)/m. För att verifiera den beräknade styvheten togs en FE-modell fram bestående av en 30m hög vägg lastad horisontellt i dess plan med en eller två vertikala fogar där en linjär styvhet applicerades. Utböjningen samt reaktionskrafterna noterades, resultatet för den uträknade linjära styvheten jämfördes med andra styvheter och bedömdes utifrån detta vara rimlig. Reaktionskrafterna visade sig vara beroende av styvheten på fogen. Den sänkta skjuvmodulen för håldäcken och den beräknade linjära elasticiteten för väggarna användes sedan i en FE-modell av en 10-våningsbyggnad med två stabiliserande enheter där de vertikala reaktionskrafterna analyserades. Resultatet visade att endast 0.02 procentenheter skiljer reaktionskrafterna i de stabiliserande enheterna då hänsyn tas till fogarna mellan håldäcken och 0.09 procentenheter då hänsyn tas till fogarna mellan väggarna. Resultatet skiljer sig från när endast väggen modellerades, vilket tros bero på att bjälklaget hjälper till att motverka deformationer i väggfogarna. Fogen mellan bjälklagselementen tros kunna ha större inverkan på en byggnad med stabiliserande enheter som drastiskt ändrar styvhet från ett plan till ett annat, i dessa fall kan den framtagna reduktionsfaktorn vara av nytta.
Malm, Richard. "Shear cracks in concrete structures subjected to in-plane stresses." Licentiate thesis, KTH, Civil and Architectural Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4215.
Повний текст джерелаAfter only two years of service, extensive cracking was found in the webs of two light-rail commuter line bridges in Stockholm, the Gröndal and Alvik bridges. Due to this incident it was found necessary to study the means available for analysing shear cracking in concrete structures subjected to in-plane stresses. The aim of this PhD project is to study shear cracking with these two bridges as reference. In this thesis, the first part aims to study the possibility of using finite element analysis as a tool for predicting shear cracking for plane state stresses. The second part is concerning how the shear cracks are treated in the concrete design standards.
Shear cracking in reinforced beams has been studied with non-linear finite element analyses. In these analyses the shear cracking behaviour was compared to experiments conducted to analyse the shear failure behaviour. Finite element analyses were performed with two different FE programs Abaqus and Atena. The material model used in Atena is a smeared crack model based on damage and fracture theory with either fixed or rotated crack direction. The material model used in Abaqus is based on plasticity and damage theory. The fixed crack model in Atena and the model in Abaqus gave good results for all studied beams. For the two studied deep beams with flanges the results from the rotated crack model were almost the same as obtained with the fixed crack model. The rotated crack model in Atena gave though for some beams a rather poor estimation of the behaviour.
The calculation of crack widths of shear cracks has been studied for the long-term load case in the serviceability state for the Gröndal and Alvik bridges, with the means available in the design standards. The methods based on the crack direction corresponding to the principal stress and do not include the effect of aggregate interlocking seems to be too conservative. Two of the studied methods included the effect of aggregate interlocking, it was made either by introducing stresses in the crack plane or implicitly by changing the direction of the crack so that it no longer coincide with the direction of principal stress. For calculations based on probable load conditions, these methods gave estimations of the crack widths that were close to the ones observed at the bridges. Continuous measurements of cracks at the Gröndal and the Alvik bridges have also been included. Monitoring revealed that the strengthening work with post-tensioned tendons has, so far, been successful. It also revealed that the crack width variations after strengthening are mainly temperature dependent where the daily temperature variation creates movements ten times greater than those from a passing light-rail vehicle. Monitoring a crack between the top flange and the webs on the Gröndal Bridge showed that the top flange was moving in a longitudinal direction relative to the web until the strengthening was completed. The crack widths in the sections strengthened solely by carbon fibre laminates seem to increase due to long-term effects.
Shehata, Emile F. G. "Fibre-reinforced polymer (FRP) for shear reinforcement in concrete structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0001/NQ41626.pdf.
Повний текст джерелаAhmad, Syed Iftikhar. "Flexural and shear strengthening of concrete structures with prestressed GFRP sheets." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/29336.
Повний текст джерелаJaafar, Kamal Rachid. "Spiral shear reinforcement for concrete structures under static and seismic loads." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616166.
Повний текст джерелаWong, Sze-man. "Seismic performance of reinforced concrete wall structures under high axial load with particular application to low-to moderate seismic regions." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B34739531.
Повний текст джерелаOlimb, Ane Marte. "Testing of Fibre Reinforced Concrete Structures : Shear Capacity of Beams with Openings." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18527.
Повний текст джерелаCarolin, Anders. "Strengthening of concrete structures with CFRP : shear strengthening and full scale applications." Licentiate thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17937.
Повний текст джерелаGodkänd; 2001; 20070316 (ysko)
Yamamoto, Taira. "Nonlinear finite element analysis of transverse shear and torsional problems in reinforced concrete shells." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0002/MQ45940.pdf.
Повний текст джерелаNordbrøden, Hanna Haugen, and Siri Hansen Weydahl. "Testing of Fibre Reinforced Concrete Structures : Shear Capacity of Beams with Corbel-End." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18561.
Повний текст джерелаBin, Mohamed Zainai. "Shear strength of reinforced concrete wall-beam structures : upper-bound analysis and experiments." Thesis, University of Cambridge, 1987. https://www.repository.cam.ac.uk/handle/1810/244866.
Повний текст джерелаKhan, Jalil Mohammad. "Nonlinear response of reinforced concrete coupling members in earthquake-resisting shear wall structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq29605.pdf.
Повний текст джерелаMorphy, Ryan David. "Behaviour of fibre-reinforced polymer (FRP) stirrups as shear reinforcement for concrete structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0002/MQ45102.pdf.
Повний текст джерелаKhan, Mohammad Jalil. "Nonlinear response of reinforced concrete coupling members in earthquake-resisting shear wall structures." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=27232.
Повний текст джерелаIn the first specimen a central reinforcement cage was provided in the slab between the shear walls. In the second and third models this central cage was replaced by a longitudinal beam. In addition, transverse concealed beams were provided at critical wall-toe regions. The flexural capacities of the concealed transverse beams were different in the second and third specimen. All these specimens were tested under progressively increasingly relative displacements being imposed between the walls. The force-displacement characteristics, reinforcement strains and the wall deflection profiles are presented.
The results of the tests were found to be in a good agreement with those of the previous studies by Taylor (8) and by Malyszko (15). The horizontal legs of the stirrups in the central cage were found to be effective in confining the excessively cracked concrete at higher displacement ductilities. The longitudinal beam along with transverse concealed beams effectively controlled the punching shear failure at the critical wall-toe regions. The transverse concealed beams were also helpful in distributing the concentrated deformations across the width of the slab.
Gwozdziewicz, Piotr. "Time analysis of prestressed concrete structures with accounting for bending and shear effects." Clermont-Ferrand 2, 1999. http://www.theses.fr/1999CLF22119.
Повний текст джерелаXu, Jiaming. "Computational modelling of concrete structures subjected to high impulsive loading." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20954.
Повний текст джерелаWong, Sze-man, and 黃思敏. "Seismic performance of reinforced concrete wall structures under high axial load with particular application to low-to moderate seismicregions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B34739531.
Повний текст джерелаRubiano-Benavides, Nestor Roberto. "Predictions of the inelastic seismic response of concrete structures including shear deformations and anchorage slip /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Повний текст джерелаSchuman, Paul Michael. "Mechanical anchorage for shear rehabilitation of reinforced concrete structures with FRP : an appropriate design approach /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3158466.
Повний текст джерелаMirtalaie, Kamal. "Shear transfer between precast prestressed bridge beams and in-situ concrete crosshead in continuous structures." Thesis, University of Leeds, 1988. http://etheses.whiterose.ac.uk/310/.
Повний текст джерелаCardinetti, Filippo <1980>. "Fiber beam-columns models with flexure-shear interaction for nonlinear analysis of reinforced concrete structures." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3989/1/Fiber_beam-columns_models_with_flexure-shear_interaction_for_nonlinear_analysis_of_reinforced_concrete_structures.pdf.
Повний текст джерелаCardinetti, Filippo <1980>. "Fiber beam-columns models with flexure-shear interaction for nonlinear analysis of reinforced concrete structures." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3989/.
Повний текст джерелаAdam, Viviane [Verfasser], Josef [Akademischer Betreuer] Hegger, Luc R. [Akademischer Betreuer] Taerwe, and Oliver [Akademischer Betreuer] Fischer. "Shear in reinforced concrete structures without shear reinforcement : analysis and design / Viviane Felizitas Adam ; Josef Hegger, Luc R. Taerwe, Oliver Fischer." Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/1241401454/34.
Повний текст джерелаZaghlool, Baher SalahElDeen Othman Ahmed. "Behaviour of three-dimensional concrete structures under concurrent orthogonal seismic excitations." Thesis, University of Canterbury. Civil Engineering, 2007. http://hdl.handle.net/10092/1177.
Повний текст джерелаFerreira, Denise Carina Santos. "A model for the nonlinear, time-dependent and strengthening analysis of shear critical frame concrete structures." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/116540.
Повний текст джерелаLos modelos de vigas, debido a su simplicidad inherente y eficiencia computacional, pueden ser alternativas adecuadas a complejos modelos de elementos finitos planos y sólidos. Sin embargo, el comportamiento de elementos estructurales de hormigón sometidos a fuertes esfuerzos cortantes, no pueden ser correctamente simulado mediante estos modelos, ya que no consideran los efectos no lineales del cortante y la interacción cortante-flexión. A su vez, la presencia del cortante en el hormigón armado fisurado da lugar a un complejo mecanismo resistente cuya modelización no está aún claramente definida. En esta tesis si propone un modelo de vigas que considera la no linealidad y el comportamiento paso-a-paso en el tiempo de estructuras porticadas de hormigón construidas evolutivamente teniendo en cuenta los efectos del cortante. El modelo se basa en una formulación existente de flexión y está concebido para el análisis de estructuras planas porticadas de hormigón armado (HA) y pretensado sometido a la acción combinada del esfuerzo axil, flexión y cortante. La interacción cortante-flexión si consigue mediante una formulación seccional basada en suposiciones mixtas de cinemática y fuerza. Las características clave del modelo son: (i) a nivel del material el HA se simula mediante una aproximación de fisuración distribuida rotacional; (ii) a nivel de la fibra un procedimiento iterativo garantiza el equilibrio entre el hormigón y la armadura transversal, permitiendo calcular el estado biaxial de tensiones y deformaciones en cada fibra; (iii) a nivel de la sección un patrón de tensiones tangenciales constantes estima la distribución interna de tensiones y deformaciones de cortante y (iv) a nivel del elemento se aplicada la formulación del elemento de viga Timoshenko. De este modo, los aspectos relevantes de la formulación propuesta se resumen en: (i) su capacidad para considerar los efectos del cortante en estados de servicio y últimos; (ii) el procedimiento paso-a-paso en el tiempo permite tener en cuenta la respuesta diferida debido a fluencia y retracción del hormigón, variaciones de temperatura y relajación del pretensado considerando el estado multiaxial de tensiones y deformaciones en las fibras y; (iii) el análisis secuencial permite evaluar los efectos del refuerzo teniendo en cuenta el estado de la estructura antes de la intervención El modelo se valida mediante ensayos experimentales disponibles en la literatura, así como, a través de una campaña experimental realizada por la autora, demostrando su capacidad para reproducir la respuesta de vigas críticas a cortante. La importancia de incluir la interacción cortante-flexión en el análisis numérico es destacada por medio de la comparación de los resultados con los proporcionados por el modelo básico de flexión. Con el modelo propuesto se estudia la influencia del cortante en la respuesta diferida de vigas dominadas por cortante y flexión. La consideración de los efectos del cortante es relevante en la modelación de la respuesta diferida de vigas de HA con fisuras diagonales y en vigas pretensadas. El modelo propuesto se compara con éxito con los resultados experimentales de una viga dañada a cortante y posteriormente reforzada mediante un recrecido de hormigón y armadura transversal. Adicionalmente, se analiza numéricamente otra solución alternativa de refuerzo basada en estribos pretensados. La importancia de considerar el daño previo de la viga reforzada queda demostrada en la evaluación numérica. Finalmente, se simula la respuesta de un puente pretensado desmantelado con deficiente resistencia a cortante y sometido a ensayos de carga a larga-escala. Son también estudiadas diferentes propuestas de refuerzo basadas en soluciones de pos-tensado. De este modo, se demuestra la capacidad del modelo para determinar la seguridad de estructuras existentes y analizar la eficiencia de las medidas de refuerzo.
Haas, Martin. "Investigations on shear including the development of a material model for the FE analysis of cracked RC structures." Thesis, University of Sheffield, 1996. http://etheses.whiterose.ac.uk/3534/.
Повний текст джерелаLim, Albert Kee Wah. "Non-linear response of reinforced concrete coupling slab with drop panel in earthquake-resisting shear wall structures." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55618.
Повний текст джерелаNeagoe, Catalin Andrei. "Structural performance of FRP-concrete hybrid beams with flexible shear connection." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/397749.
Повний текст джерелаSustainability of buildings and public infrastructure is a relatively recent topic put into discussion by the engineering community. A solution to designing structures that have long-term durability and low maintenance requirements is to introduce new construction materials or to implement new structural systems. In this regard, fiber reinforced polymers (FRP) represent one of the novel solutions in the civil engineering field that offer promising results. To optimize the use of FRP shapes, researchers have proposed to form hybrid structural systems by combining the composite materials with conventional materials, such as concrete, in order to improve on the stiffness, ductility, and buckling resistance of single FRP members. However, due to the novelty and wide variety of hybrid elements, the technology demands further experimental testing to prove its viability. In addition, because there is a current lack of mandatory codes for the design of structures built with composite profiles and consequently FRP-concrete members, reliable predictive models have to be developed. Addressing the above-mentioned issues is essential in lessening the introduction of advanced composite materials in common types of public works and constructions. The present research aimed thus to study the structural performance of hybrid beams made of FRP pultruded profiles attached to concrete slabs by carrying an experimental, analytical, and numerical investigation. Since interface slip effects had been largely overlooked in the past, the thesis focused also on the influence of the connection flexibility over bending behavior. With respect to the developed experimental campaign, eight glass FRP-concrete hybrid beams with mechanical shear connectors were fabricated and their flexural behavior was assessed against that of equivalent reinforced concrete beams and single GFRP structural profiles. The variables of the research were the type of hybrid cross-section and the concrete strength class. The laboratory campaign was divided in two phases depending on the specific test setup configuration, and observations were made regarding the short-term behavior of the novel elements under positive bending moments. Previous to the experimental tests, a nondestructive characterization procedure was proposed for obtaining the elastic properties of the constitutive materials of hybrid members in a reduced amount of time, by using an analysis of the free vibration response. Overall, the bending tests have demonstrated the high structural efficiency of the hybrid beam solution and have underlined the importance of accounting for shear connection deformability. An analytical procedure was introduced for the design of FRP-concrete beams under short-term loading. Design equations for the serviceability and ultimate limit states were proposed in function of complete or partial shear interaction assumptions. The feasibility of using simplified formulas to quantify for interlayer slip effects was studied in evaluating deflections, flexural stiffness, bending capacities, normal and shear stress distributions. Due to the improved precision of the expressions that had considered the shear connection flexibility, the proposed analytical procedure was able to capture appropriately the structural behavior and performance of the specimens. Finally, referring to the numerical analyses, predictive finite element models capable of simulating the fundamental behavior of FRP-concrete beams with bolted joints were developed. The model that included material, contact, and geometry nonlinearities offered the best results in comparison with the experimental data and analytical estimations. Concrete slab crushing and cracking, tension stiffening effects, interface friction, and the elasto-plastic behavior of the shear connectors were all taken under consideration.
Mensah, Kenneth Kwesi. "Reliability assessment of structural concrete with special reference to shear resistance." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19967.
Повний текст джерелаENGLISH ABSTRACT: Structural design standards based on the principles of structural reliability are gaining worldwide acceptance and are fast becoming the new basis of structural safety verification. The application of these principles to establish a standardised basis for structural design using partial factor limit states design procedures is done in the European Standard for the Basis of Structural Design EN 1990 from which it is adapted to the South African Basis of Design Standard for Building and Industrial Structures SANS 10160-1. The basis of design requirements stipulated in EN 1990 and SANS 10160-1 apply to all aspects of structural design: This includes reliability levels of structural performance and their differentiation and management; identification of various limit states and design situations; the specification of all the basic variables; separate treatment of actions and material-based resistance. However, application of these requirements is then primarily focused on actions whilst the provision for structural concrete is then left to the materials based design standards. This two-part thesis describes a systematic assessment of the degree to which the application of the reliability framework presented in the basis of design requirements has been achieved in the present generation of structural concrete design standards. More importantly, attempts are made to identify ways in which the process can be advanced. Special attention is drawn to issues that are specific to South African conditions and practice in structural concrete. Part One of the thesis focuses on the key elements of the reliability framework presented in EN 1990 and traces to what extent the requirements have been propelled through the design stipulations of the Eurocode Standard for Design of Concrete Structures EN 1992-1-1. The implications of the different reference level of reliability between the Eurocode default value of ß = 3.8 and that characteristic of South African practice ß = 3.0 through various issues are highlighted. The use and advantage of explicit treatment of reliability performance on reliability management related to some aspects of quality control are explored. A critical aspect is the shear prediction model providing unconservative estimates of shear resistance. Part Two of the thesis focuses on characterising the model factor of the EN 1992-1-1 shear prediction model for members requiring design shear reinforcement. This is done by a comparison to a compiled experimental database with special focus on situations with high reinforcement ratios. The significance of the modelling uncertainty in shear prediction is verified by this comparison. The use of the more conceptually rational modified compression field theory (MCFT) to improve on the quality of shear predictions is investigated and proves to yield more precise values with lower scatter hence making it a more reliable tool for predicting shear. The MCFT can then be used as reference for the reliability calibration and possible improvement for the Eurocode procedure.
AFRIKAANSE OPSOMMING: Strukturele ontwerpstandaarde gebaseer op die beginsels van strukturele betroubaarheid verkry wêreldwye aanvaarding en word vinnig die nuwe basis van strukturele veiligheid bevestiging. Die toepassing van hierdie beginsels om ʼn gestandaardiseerde basis vir strukturele ontwerp is bevestig deur gebruik te maak van gedeeltelike-faktorbeperkende stadiums ontwerpprosedures in die Europese Standaard vir die Basis van Strukturele Ontwerp EN 1990 waarvandaan dit herbewerk is na die Suid-Afrikaanse Basis van Ontwerp Standaarde vir Bou en Industriële Strukture SANS 10160-1. Die basis van ontwerpvereistes bepaal in EN 1990 en SANS 10160-1 is van toepassing op alle aspekte van strukturele ontverp: Dit sluit inbetroubaarheidsvlakke van struktureele prestasie en hul diversifikasie en bestuur; identifikasie van verskeie beperkende state en ontwerpsituasies; die spesifikasie van al die basiese veranderlikes; afsonderlike behandeling van aksies en materiaal-gebaseerde weerstand. Desnieteenstaande, die toepassing van hierdie voorwaardes is dan hoofsaaklik gefokus op aksies terwyl die voorsiening van strukturele beton is dan gelaat op die materiaalgebaseerde ontwerpstandaarde. Hierdie tweeledige verhandeling beskryf ʼn stelselmatige beoordeling van die graad waartoe die toepassing van die betroubaarheidsraamwerk aangebied word in die basis van ontwerpvereistes bereik in die huidige generasie van strukturele beton-ontwerp standaarde is. Meer belangrik, pogings is aangewend om die maniere hoe die proses bevorder kan word te identifiseer. Spesiale aandag word gevestig op kwessies wat spesifiek op Suid-Afrikaanse toestande en praktyke in strukturele beton toepaslik is. Deel Een van die verhandeling fokus op die sleutel-dele van die betroubaarheidsraamwerk aangebied in EN 1990 en skets die mate waartoe die vereistes aangespoor word deur die ontwerp voorskrifte van die Eurocode Standard for the Design of Concrete Structures EN 1992-1-1. Die implikasie van die verskillende verwysingsvlakke van betroubaarheid tussen die Eurocode standaardwaarde van ß = 3.8 en die eienskap van Suid-Afrikaanse praktyk ß = 3.0 deur verskillende kwessies word uitgelig. Die gebruik en voordeel van spesifieke behandeling van betroubaarheidsuitvoering op betroubaarheidsbestuur verwantskap met sekere aspekte van kwaliteit kontrole word ondersoek. ʼn Kritiese aspek is die model vir die voorspelling van skuif-weerstand wat die onkonserwatiewe beramings vir skuif-weerstand gee. Deel Twee van die verhandeling fokus op karakterisering die modelfaktor van die EN 1992- 1-1 skuif-weerstand voorspellings-model. Dit word gedoen deur ʼn vergelyking na ʼn saamgestelde eksperimentele databasis met spesifieke fokus op situasies met hoe herbevestigingsvergelykings. Die oorheersing van die modellering- onsekerheid in skuifweerstand voorspelling is bevestig deur hierdie vergelyking. Die gebruik van ʼn meer konseptuele rasionele gemodifiseerde druk-veld teorie (bekend as MCFT) om die kwaliteit van skuif voorspelling te verbeter is ondersoek en verskaf ‘n meer presiese waarde met laer verspreiding wat lei tot ʼn meer betroubaree instrument om skuif mee te voorspel. Die MCFT word dan gebruik as verwysing vir die betroubaarheid-samestelling en moontlike verbetering van die Eurocode prosedures.
Tuken, Ahmet. "Quantifying Seismic Design Criteria For Concrete Buildings." Phd thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/12604907/index.pdf.
Повний текст джерелаBorland Delphi&rdquo
, have been developed to make the analysis and design easy for the engineer. A method is also developed to satisfy the ductility requirement of composite buildings subject to lateral seismic loading based on a plastic analysis. The commonly accepted sway ductility of &
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Uduehi, June. "Comparative study of the structural behaviour of prestressed beams of brickwork and concrete and the shear strength of brickwork beams." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/11485.
Повний текст джерелаZhang, Xuesong, and n/a. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion." Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051104.153239.
Повний текст джерелаZhang, Xuesong. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion." Thesis, Griffith University, 2003. http://hdl.handle.net/10072/365777.
Повний текст джерелаThesis (Masters)
Master of Philosophy (MPhil)
School of Engineering
Full Text
Černý, Pavel. "Mostní nadjezd přes dálnici." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2020. http://www.nusl.cz/ntk/nusl-409788.
Повний текст джерелаBlanksvärd, Thomas. "Strengthening of concrete structures by the use of mineral based composites : system and design models for flexure and shear." Doctoral thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26504.
Повний текст джерелаEn betydande del av samhällets tillgångar är investerade i vår existerande infrastruktur som t ex järnvägsbroar, vägbroar, tunnlar, dammar,, fastigheter etc. En majoritet av dessa konstruktioner är byggda av armerad betong. Samtliga av dessa betongkonstruktioner har både en förväntad funktion och en förväntad livslängd. Men både funktionen och livslängden kan komma att ändras på grund av yttre påverkande faktorer som till exempel nedbrytning och förändrade belastningsförhållanden. Ytterligare kan vara tidiga misstag i projekteringsfasen eller under själva uppförandet. Genom reparation och/eller förstärkning kan både funktion och livslängd hos dessa konstruktioner ofta återställas eller till och med uppgraderas. Förstärkning av betongkonstruktioner genom att limma fast kolfiberväv eller kolfiberkompositer har visat sig vara en bra och tillförlitlig metod för att öka bärförmågan hos befintliga konstruktioner. Det lim som till största delen används vid denna typ av förstärkning är epoxilim. Dessvärre har epoxilim vissa nackdelar, så som diffusionstäthet, dålig termisk kompabilitet med betong och krav på skyddad arbetsmiljö. Ytterligare en begränsande faktor är kravet på omgivande temperatur vid limning. Vissa av dessa nackdelar kan reduceras genom att byta ut epoxilimmet mot en mineralbaserad vidhäftningsprodukt med egenskaper liknande betongens.Förstärkningssystemet som omfattas av denna avhandling har benämningen "mineralbaserade kompositer" (MBC) och omfattar kolfibernät med hög draghållfasthet som fästs på befintlig betongkonstruktion med ett cementbaserat bruk.Det vetenskapliga förfarandet i denna avhandling omfattar analytiska metoder för att beskriva bärförmågan för den förstärkta betongkonstruktionen i både böjning och tvärkraft. De analytiska metoderna är sedan verifierade mot laboratorieförsök. Utöver de teoretiska och experimentella resultaten för MBC systemet så ingår även en aktuell granskning och kartläggning av existerande mineralbaserade förstärkningssystem och därmed möjliga materialkombinationer och utformningar, dvs. andra än MBC systemet.Avhandlingen består av en litteraturstudie och sex bifogade artiklar.Den första artikeln beskriver hur MBC system uppför sig vid förstärkning i böjning. I denna artikel ingår provning av en större betongplatta som förstärkts med MBC systemet och epoxibaserade system samt en parametersstudie på småskaliga provkroppar med MBC systemet och olika cementbaserade bruk.Den andra artikeln beskriver hur förstärkningssystemet presterar vid förstärkning i tvärkraft. Denna studie omfattar experimentella resultat på 23 balkar med olika betongkvalitéer, armeringsmängd samt olika variationer av MBC systemet och jämförelse mot traditionell epoxibaserad förstärkning. Dessutom innehåller denna artikel en analytisk uppskattning av tvärkraftskapaciteten.Den tredje artikeln beskriver olika existerande förstärkningssystem och hur dessa presterar i jämförelse med MBC systemet i böjning och tvärkraft.Den fjärde artikeln kartlägger olika möjligheter till att kombinera material i mineralbaserade förstärkningssystem för att optimera dessa system. Dessutom ingår även experimentella försök med ett högpresterande fiberförstärkt cementbruk (ECC). Denna artikel omfattar även resultat och diskussion om MBC systemets beteende i enaxligt drag, brottenergiupptagande förmåga samt hur dessa observationer kopplas till iakttagelser i böj- och tvärkraftsförstärkning.Den femte artikeln behandlar en rekommendation till dimensionering för tvärkraft av MBC systeme baserat på traditionella dimensioneringsmetoder med fackverksteori samt en ny tillämpning baserat på tryckfältsteori.Det sjätte bidraget beskriver hur töjningsutvecklingen sker i tvärkraft för betongbalkar med och utan MBC systemet.Resultaten från dessa undersökningar indikerar på att MBC systemet bidrar till att öka bärförmågan hos förstärkta betongelement och att denna ökning kan i vissa avseenden jämföras mot epoxibaserad förstärkning. Det är även visat att MBC systemet, i tvärkraftsförstärkning, bidrar till att minska töjningar i det armerade betongtvärsnittet i övergångszonen mellan tillväxten av mikrosprickor till makro sprickor samt att töjningarna reduceras även under öppningen av makrosprickor. Analytiska metoder för att uppskatta bärförmåga för förstärkning i böjning och tvärkraft är redovisade och dessa indikerar på att realistiska uppskattningar är möjliga. Dimensionering av bärförmågan i böjning är relativt enkel medan dimensionering i tvärkraft är lite mer komplicerad. En av slutsatserna gällande tvärkraftsdimensioneringen är att det är möjligt på ett enkelt sätt använda befintliga dimensionerings anvisningar grundade i "additions" principen för att uppnå en säker uppskattning av bärförmågan i tvärkraft.
Godkänd; 2009; 20090313 (thojoh); DISPUTATION Ämnesområde: Konstruktionsteknik Opponent: Professor Thanasis C Triantafillou, University of Patras, Grekland Ordförande: Professor Björn Täljsten, Technical University of Denmark och Luleå tekniska universitet Tid: Fredag den 24 april 2009, kl 10.00 Plats: F 1031, Luleå tekniska universitet
Wieneke, Katrin Marie [Verfasser], Josef [Akademischer Betreuer] Hegger, and Linh Cao [Akademischer Betreuer] Hoang. "Horizontal shear design of concrete interfaces in beam and slab structures / Katrin Marie Wieneke ; Josef Hegger, Linh Cao Hoang." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1211096661/34.
Повний текст джерелаSaadé, Katy. "Finite element modeling of shear in thin walled beams with a single warping function." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211043.
Повний текст джерелаA unified approach is formulated in this thesis for 3D thin walled beam structures with arbitrary profile geometries, loading cases and boundary conditions. A single warping function, defined by a linear combination of longitudinal displacements at cross sectional nodes (derived from Prokic work), is enhanced and adapted in order to qualitatively and quantitatively reflect and capture the nature of a widest possible range of behaviors. Constraints are prescribed at the kinematics level in order to enable the study of arbitrary cross sections for general loading. This approach, differing from most published theories, has the advantage of enabling the study of arbitrary cross sections (closed/opened or mixed) without any restrictions or distinctions related to the geometry of the profile. It generates automatic data and characteristic computations from a kinematical discretization prescribed by the profile geometry. The amount of shear bending, torsional and distortional warping and the magnitude of the shear correction factor is computed for arbitrary profile geometries with this single formulation.
The proposed formulation is compared to existing theories with respect to the main assumptions and restrictions. The variation of the location of the torsional center, distortional centers and distortional rotational ratio of a profile is discussed in terms of their dependency on the loading cases and on the boundary conditions.
A 3D beam finite element model is developed and validated with several numerical applications. The displacements, rotations, amount of warping, normal and shear stresses are compared with reference solutions for general loading cases involving stretching, bending, torsion and/or distortion. Some examples concern the case of beam assemblies with different shaped profiles where the connection type determines the nature of the warping transmission. Other analyses –for which the straightness assumption of Timoshenko theory is relaxed– investigate shear deformation effects on the deflection of short and thin beams by varying the aspect ratio of the beam. Further applications identify the cross sectional distortion and highlight the importance of the distortion on the stresses when compared to bending and torsion even in simple loading cases.
Finally, a non linear finite element based on the updated lagrangian formulation is developed by including torsional warping degrees of freedom. An incremental iterative method using the arc length and the Newton-Raphson methods is used to solve the non linear problem. Examples are given to study the flexural, torsional, flexural torsional and lateral torsional buckling problems for which a coupling between the variables describing the flexural and the torsional degrees of freedom occurs. The finite element results are compared to analytical solutions based on different warping functions and commonly used in linear stability for elastic structures having insufficient lateral or torsional stiffnesses that cause an out of plane buckling.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
Tassotti, Luca. "Seismic analysis and design of innovative steel and concrete hybrid coupled wall systems." Doctoral thesis, Università Politecnica delle Marche, 2015. http://hdl.handle.net/11566/242920.
Повний текст джерелаThe concept of structural fuse applied to earthquake resistant systems has led to the development of several seismic-resistant structural solutions, including interesting steel and concrete hybrid systems. These systems are obtained through a combination in series of steel elements and reinforced concrete elements with the aim of exploiting at their best the potentialities of each material. In this work the seismic behaviour of an innovative hybrid coupled shear wall (HCSW) system, developed in the European research project INNO-HYCO (INNOvative HYbrid and COmposite steel-concrete structural solutions for building in seismic area), is investigated. The earthquake resistant solution is composed by a reinforced concrete wall coupled to steel side columns by means of easily replaceable steel links with the objective to exploit both the stiffness of reinforced concrete wall, necessary to limit building damage under low-intensity earthquakes, and the ductility of steel links, necessary to dissipate energy under medium- and high-intensity earthquakes. The seismic behaviour of the system is assessed through nonlinear static (pushover) analysis and multi-record nonlinear incremental dynamic analysis (IDA). For this purpose, firstly a set of realistic case studies is designed, then a finite element model is developed into the platform Opensees and validated through comparisons against experimental tests including local and global responses quantities. A selection of results including global and local response quantities is shown in order to highlight the potentialities of the proposed innovative HCSW systems and the actual possibility to develop a ductile behaviour where plastic deformation are attained in the steel links before yielding in the reinforced concrete wall. The final results permit to provide a support for the identification of optimal solutions that could be competitive against existing seismic resistant structural systems.
Gunel, Orhun Ahmet. "Influence Of The Shear Wall Area To Floor Area Ratio On The Seismic Performance Of Existing Reinforced Concrete Buildings." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615678/index.pdf.
Повний текст джерелаOlsson, Daniel. "Numerical simulations of energy absorbing boundaries for elastic wave propagation in thick concrete structures subjected to impact loading." Thesis, Umeå universitet, Institutionen för fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-58015.
Повний текст джерелаMånga av världens kärnkraftverk närmar sig slutet på sin beräknade livslängd och ett behov uppstår då att kunna utvärdera de komponenter som är väsentliga för säkerheten på dessa verk. Reaktoromslutningen i betong är en av dessa komponenter och oförstörande provning (NDT) är en attraktiv metod för att bedöma dess tillstånd. Traditionellt har utvärdering av betongkonstruktioner bestått av stresstester på borrprover men p.g.a. den radioaktiva miljön på insidan av omslutningen är denna metod ej att föredra. NDT är självklart möjligt att använda på allsköns betongkonstruktioner då det ger både konstruktionsmässiga och estetiska fördelar. NDT metoden som rör denna studie kallas impact echo och går ut på att man med en hammare slår till en punkt på väggen och mäter responsen en bit därifrån. Lasten ger upphov till vågor i form av deformation som propagerar i väggen och dessa ger i sin tur upphov till Lamb moder. Lamb moderna är strukturella oscillationer av väggen och genom att studera dess frekvenser kan väggens tjocklek bestämmas. Elastiska egenskaper i väggen erhålls utifrån de olika vågornas propageringshastigheter. Impact echo metoden kan även användas för att finna strukturella oegentligheter inuti väggen så som sprickor och delaminering. För att utföra numeriska simuleringar av dynamiska system med NDT-metoder är finita elementmetoden (FEM) användbar. Syftet med denna studie är att bedöma vilka möjligheter som finns för att implementera absorberande ränder med ökande dämpning (ALID) i datamodeller för att minska beräkningstiden av FEM-analyser. ALID används vid kanterna för att simulera ett oändligt system, dess uppgift är att dämpa bort inkommande vågor så att dessa ej reflekteras tillbaka och stör mätningarna. Samtliga modeller i denna studie är två-dimensionella med antagen oändligt liten spänning i normalriktningen. Vinsten i beräkningstid av att använda ALID är stor och ökar ytterligare om modellen utökas till tre dimensioner. Ett ALID definieras genom dess längd och maximala massproportionerlig Rayleigh-dämpning (CMmax). I denna rapport har längderna 0.5, 1.5 and 4.5 m använts med CMmax i intervallet från 103 till 2*105 Ns/m. Dämpningen ökar med ökat avstånd in i ALID med det specificerade maxvärdet vid den bakre kanten. Det bör noteras att skillnad i dämpning mellan element leder till skillnad i impedans; reflektioner av vågorna uppstår vid övergång från ett element med lägre impedans till ett med högre impedans. Ett ALID måste således vara definierat så att det dämpar bort tillräckligt av de inkommande vågorna utan att oönskade reflektioner i ALID uppstår. Studien pekar på att ett 0.5 m långt ALID inte åstadkommer önskvärda resultat för något av valen för CMmax som använts i denna rapport. Både det 1.5 och 4.5 m långa ALID har däremot get bra resultat; ett 1.5 m långt ALID bör ha 2*104 < CMmax <5*104 Ns/m och ett 4.5 m långt ALID 5*103 < CMmax < 104 Ns/m. Förhoppningen med studien är att resultaten skall underlätta utvecklingen av NDT-metoder som kan användas vid konstruktion och underhåll av reaktoromslutningar och andra tjocka betongkonstruktioner.