Betono senėjimo koeficientas – tai pagrindinis rodiklis, kuris įvertina betono įtempių kitimą per laiką prognozuojant gežbetoninių elementų įlinkius, įtemptojo gelžbetonio armatūros nuostolius dėl betono valkšnumo ir t.t. Senėjimo keoficieno faktiškai neįmanoma gauti analitine forma iš Volterra integrodiferencialinės lygties, todėl jam yra taikomos skaitiniu būdu gautų rezultatų aproksimacijos arba tiesiog jis imamas apytiksliai lygus 0,8 nediferencijuojant tokių faktorių, kaip betono amžius, stebėjimo laikas, betono stirprumas, armaturos kiekis ir t.t. Baigiamajame magistro darbe atlikta įvairių autorių pasiūlytų empirinių betono senėjimo koeficiento formulių analizė. Nustatytos betono senėjimo koeficiento empirinių formulių kitimo ribos ir jų legitimumas tikslioms, skaitiniu būdu gautoms senėjimo koeficiento reikšmėms. Darbe, taikant vidutinių ekvivalentinių įtempių ir deformacijų metodą (ASSA), yra analitiškai išvestas koeficientas, leidžiantis įvertinanti armatūros įtaką gelžbetoniniam elementui, apkrautam pastovia per laiką jėga priklausomai nuo betoninio elemento, apkrauto nekintamu laiko atžvilgiu poslinkiu (grynosios relaksacijos uždavinys). Atlikta armavimo koeficiento įtakos betono senėjimo koeficientui analizė, gauti rezultatai palyginti su tiksliomis reikšmėmis bei EC-2 rekomenduojama viena reikšme - 0,8. Darbe suformuluotas senėjimo koeficiento neapibrėžtumo įvertinimo stochastinis uždavinys. Atlikta parametrų analizė, siekiant nustatyti kiekvieno jų įtaką... [toliau žr. visą tekstą] / The coefficient of aging is the major parameter accounting for the stress evolution in time in deflection analysis of reinforcement concrete elements and specification for losses of pre-stress due to concrete creep. This parameter cannot be derived analytically from Volterra's integro-differential equation and numerical solution is always feasible. Hence, the empirical formula to fit the numerically-based results for the coefficient of aging can be found in literature on the matter. In particular, the code Ec-2 uses a only one value for this coefficient equal to 0.8 neglecting the influence of concrete strength, its age, quantity of reinforcement, time of consideration, etc., and it is cleat that such attempt is quite scarce. Thereby, in the master's thesis, the analysis of various approximate relationships for the coefficient of aging found in literature is considered. Here, a legitimacy of these relations is defined in terms of numerically-based results and the error bounds is determined. The analytical derivation of factor specifying the conversion from a pure relaxation test of plain concrete to the reinforced concrete element is demonstrated via an average strain stress approach (ASSA). The influence of reinforcement quantity on the coefficient of aging is considered comparing the numerical values, EC-2 based value of 0.8 and values defined by empirical relations. Also, the stochastic formulation to define the uncertainties of coefficient of aging related to variation... [to full text]

The goal of this thesis was the verification of the advanced time-dependent elasto-plastic material model for modeling diaphragm walls. Currently, this type of construction is solved usually with a combination of linear-elastic volume and plate elements. To express time-dependent behaviour, there are both, volume and plate, elements active in short-term conditions, then only volume elements in long-term conditions, while plate elements are deactivated. In this thesis, the Shotcrete material model, which can capture the time-dependent behaviour without combining two types of construction elements, is used. First, a theory of time-dependent behaviour is presented and a design of concrete structures by Eurocode 2 is discussed. Next, the Shotcrete material model is described, then used for modeling a biaxial test and calibration of compression and bending test. Following the gained knowledge, a real boundary value problem of deep excavation supported by diaphragm walls with the strut was solved. To calculate values of the internal forces and horizontal deformation in diaphragm walls, three types of material models are used.

The presented paper deals with a theoretical analysis of the ultimate limit state. The results of experimental research carried out at the Institute of Metal and Timber Structures headed by Assoc. Prof. Karmazinová and Professor Melcher were applied. The geometrically and materially nonlinear solution based on the Timošenko’s solution is verified by the FEM model in the computer programme system ANSYS. The random influence of initial imperfections is taken into consideration. The FEM model also includes the influence of residual stress. In the parametric study, the influence of residual stress on the cross-section plastification is researched into, its influence on the load carrying capacity limit is, together with the influence of other imperfections, the subject of the stochastic analysis, applying the Latin Hypercube Sampling (LHS). Further on, the study proves a direct effect of the concrete part of the cross-section (combination of materials steel-concrete) on the decrease of load carrying capacity limit of the beam caused by influence of the residual stress of steel. With regard to the importance of time dependent phenomena of the concrete creep for the load carrying capacity, the studies given in the Ph.D. thesis are oriented in this respect. The parametric studies of the influence of the concrete creep having applied the Standard Eurocode 2 provide both a comparison of load carrying capacity limits when using common and high-strength concrete types, and also the variability of load carrying capacities. It follows from the comparison of the statistical analysis outputs according to the design reliability conditions of the Standard EN1990 and of the approach of Eurocode 4 that the Eurocode 4 can be recommended for dimensioning of this member type. According to the studies which we carried out, the design in compliance with Eurocode 4 can be evaluated as the reliable one. A larger set of experimental data is necessary to determine the economy.

The diploma‘s thesis deals with the design and assessment of prestressed cocrete tank of biogas station at ultimate limit state and also at serviceability limit state, according to ČSN EN 1992-1-1: Design of concrete structures. Specifically, the design of wall of the tank and foundation slab. The text part contains general information on the desing of the structure, static idealization of the structure, type of load and method for calculation of inner forces. Attachments contain drawing documentation and structural analysis, which completes the text part and solves in detail said structure.

Tragwerke aus Stahlbeton weisen infolge des Kriechens und Schwindens des Betons ein zeitveränderliches Materialverhalten auf. Die Folge sind Umlagerungen der im Querschnittsinneren wirkende Kräfte und im Zeitverlauf zunehmende Verformungen. Zur Beurteilung dieses Langzeitverhaltens sind geeignete Berechnungsmodelle erforderlich, die im Planungsstadium eine zuverlässige Prognose ermöglichen. Dabei spielen nicht nur reine Stahlbetonkonstruktionen eine Rolle, sondern im Zuge von Ertüchtigungsmaßnahmen werden zur Erhöhung der Tragfähigkeit zunehmend auch textile Bewehrungen aus Carbon- und AR-Glasfasern eingesetzt. Durch die beanspruchungsgerecht aufzubringenden Bewehrungsstrukturen und einen speziellen Feinbeton können sehr geringe Betonschichtdicken realisiert werden. Es entsteht ein Verbundquerschnitt mit unterschiedlichen Betonrezepturen, gleichfalls unterschiedlichem Betonalter und mit mehreren verschiedenen Bewehrungskomponenten. Um Aussagen zum Langzeitverhalten derartiger Konstruktionen treffen zu können, ist eine ganzheitliche Betrachtung über alle diese im Verbund liegenden Komponenten mit ihren jeweiligen Materialeigenschaften erforderlich. Im Rahmen der vorliegenden Arbeit sind in einem ersten Schritt die Stoffgesetze für die beteiligten Materialien Beton, Stahl- und Textilfaserbewehrung zu formulieren. Im Mittelpunkt steht dabei das viskoelastische Verhalten des Betons, für dessen baumechanische Beschreibung ein geeignetes rheologisches Modell in Form einer Feder-Dämpfer-Kombination dargestellt und die zugehörige Spannungs-Dehnungs-Zeit-Beziehung hergeleitet wird. Ferner wird aufgezeigt, wie die erforderlichen Materialparameter mit Hilfe üblicher Berechnungsansätze für Kriechen und Schwinden (z.B. nach EUROCODE 2) kalibriert werden können. Die betrachteten Textilfasern werden zunächst mit linear-elastischem Verhalten in Rechnung gestellt. Auf alternative Ansätze, die auch hier viskoelastische Eigenschaften berücksichtigen, wird hingewiesen, und das Berechnungsmodell ist dahingehend erweiterbar gestaltet. In einem zweiten Schritt werden die Materialmodelle der Einzelkomponenten nach den mechanischen Grundprinzipien von Gleichgewicht und Verträglichkeit und unter der BERNOULLIschen Annahme eines eben bleibenden Querschnittes miteinander in Beziehung gesetzt. Hierfür ist eine inkrementelle Vorgehensweise erforderlich, die mit dem Zeitpunkt der ersten Lastaufbringung beginnt und schrittweise den darauffolgenden Zustand berechnet. Im Ergebnis entsteht ein Algorithmus, der die am Querschnitt stattfindenden Veränderungen im Spannungs- und Dehnungsverhalten unter Einbeziehung der Stahlbewehrung sowie einer ggf. vorhandenen Textilbetonschicht wirklichkeitsnah erfaßt. Für statisch bestimmte Systeme mit bekanntem Schnittkraftverlauf wird gezeigt, wie sich so zu jeder Zeit an jeder Stelle der vorliegende Dehnungszustand und aus diesem über die Krümmung die Durchbiegung berechnen läßt. Der dritte und für viele praktische Anwendungen wichtigste Schritt besteht darin, die am Querschnitt hergeleiteten Beziehungen in ein finites Balkenelement zu überführen und dieses in ein FE-Programm zu implementieren. Auch das gelingt auf inkrementellem Wege, wobei für jedes Zeitinkrement die Spannungs- und Verformungszuwächse aller Elemente mit Hilfe des NEWTON-RAPHSON-Verfahrens über die Iteration des Gleichgewichtszustandes am gesamten System bestimmt werden. Hierzu werden einige Beispiele vorgestellt, und es werden die Auswirkungen des Kriechens und Schwindens mit den sich daraus ergebenden Folgen für das jeweilige Tragwerk erläutert. Ferner wird gezeigt, wie textilbewehrte Verstärkungsmaßnahmen gezielt eingesetzt werden können, um das Trag- und Verformungsverhalten bestehender Bauwerke unter Beachtung des zeitveränderlichen Materialverhaltens kontrolliert und bedarfsgerecht zu beeinflussen. / Structures of reinforced concrete show a time-varying material behaviour due to creeping and shrinking of the concrete. This results in the rearrangement of the stresses in the cross-section and time-depending increase of the deformations. Qualified calculation models enabling a reliable prediction during the design process are necessary for the assessment of the long-term behavior. Not only pure reinforced concrete structures play an important role, but within retrofitting actions textile reinforcements of carbon and AR-glass fibres are applied in order to enhance the load-bearing capacity. A small concrete-layer-thickness can be achieved by the load-compatible application of reinforced textile configurations and the usage of a special certain fine-grained concrete. It leads to a composite section of different concrete recipes, different concrete ages and also several components of reinforcement. To give statements for the long-term behaviour of such constructions, a holistic examination considering all this influencing modules with their particular material properties is necessary. Within this dissertation in a first step the material laws of the participated components, as concrete, steel and textile reinforcement, are defined. The focus is layed on the visco-elastic behaviour of the concrete. For its mechanical specification a reliable rheological model in terms of a spring-dashpot-combination is developed and the appropriate stress-strain-time-relation is derived. Furthermore the calibration of the required material parameters considering creep and shrinkage by means of common calculation approaches (e.g. EUROCODE 2) is demonstrated. For the textile fibres a linear-elastic behaviour is assumed within the calculation model. It is also refered to alternative approaches considering a visco-elastic characteristic and the calculation model is configured extendable to that effect. In a second step the material models of the single components are correlated taking into account the mechanical basic principles of equilibrium and compatibility as well as the BERNOULLIan theorem of the plane cross-section. Therefore an incremental calculation procedure is required, which starts at the moment of the first load-application and calculates the subsequent configuration step by step. In the result an algorithm is derived, that realistically captures the occuring changings of stress and strain in the cross-section by considering the steel reinforcement as well as a possibly existing layer of textile concrete. For statically determined systems with known section force status it is demonstrated how to calculate the existing condition of strain and following the deflection via the curvaturve at every time and at each position. The third step - for many practical applications the most important one - is the transformation of the derived relations at the cross-section into a finite beam-element and the implementation of this in a FE-routine. This also takes place in an incremental way, whereat for each time-increment the increase of stress and strain for all elements is identified by using the NEWTON-RAPHSON-method within the iteration process for the equilibrium condition of the whole system. Meaningful numerical examples are presented and the effects of creep and shrinkage are explained by depicting the consequences for the particular bearing structure. Moreover it is shown how the purposeful use of textile reinforcement strengthening methodes can influence and enhance the load-bearing and deflection characteristics of existing building constructions by considering the time-varying material behaviour.

The purpose of the diploma thesis is to design a expressway bridge over the river Vsetínská Bečva. The bridge is located between Valašské Meziříčí and Vsetín. Separate superstructures are designed for each directions of the expressway. The right superstructure, which is wider, is considered for detailed design. Two variants were proposed, A double T beam superstructure and a box girder superstructure. The three span box girder superstructure was chosen for the design. Spans are 48+65+48 m long. Two options of construction process of the superstructure were proposed. This bridge is designed according to the limit states, the influence of construction process is considered. Structural models of construction were made as a finite element model and a plate model. Structural analysis, drawings and visualization were developed.