This thesis presents results of an experimental investigation to characterize single straight steel fiber pullout in Ultra-High Performance Concrete (UHPC). Several parameters were explored including the distance of fibers to the edge of specimen, distance between fibers, and fiber volume in the matrix. The pullout load versus slip curve was recorded, from which the pullout work and maximum pullout load for each series of parameters were obtained. The curves were fitted to an existing fiber pullout model considering bond-fracture energy, Gd, bond frictional stress, 𝛕0, and slip hardening-softening coefficient, 𝜷. The representative load-slip curve characterizing the fiber pullout behavior will be implemented into a computational modeling protocol, for concrete structures, based on Lattice Discrete Particle Modeling (LDPM). The parametric study showed that distances over 12.7 mm from the edge of the specimen have no significant effect on the maximum pullout load and work. Edge distances of 3.2 mm decreased the average pullout work by 26% and the maximum pullout load by 24% for mixes with 0% fiber volume. The distance between fibers did not have a significant effect on the pullout behavior within this study. Slight differences in pullout behavior between the 2% and 4% fiber volumes were observed including slight increase in the maximum pullout load when increasing fiber volume. The suggested fitted parameters for modeling with 2% and 4% fiber volumes are a bond-fracture energy value of zero, a bond friction coefficient of 2.6 N/mm² and 2.9 N/mm² and a slip-hardening coefficient of 0.21 and 0.18 respectively. / Master of Science

Textile reinforcement concrete (TRC) is a new building material in increasing usage in modern engineering applications. The experimental investigations of TRC reveal a multiple cracking behavior which corresponds to concrete cracking and fiber pullout mechanisms. The aim of the presented research work is the mechanical analysis of the fiber pullout mechanism under dynamical loading conditions. Appropriate constitutive material models are proposed for the matrix-fiber interface taking into consideration two main mechanical characteristics, damage behavior and rate-dependent effects. These material models are the elastic damage model, the viscoelastic model and two developed viscoelastic damage material models. Moreover, an analytical model of the fiber pullout mechanism is provided, where the governing differential equation of motion is formulated and closed analytical solutions are derived under a dynamical excitation of a harmonic pullout displacement function at the fiber tip. These analytical solutions are derived for two material models of the interface, the elastic damage and the viscoelastic material models. Furthermore, the dynamical responses are also sought for the case of a linearly increasing pullout displacement function of a definite velocity. For the latter dynamical loads a numerical DISCRETE MODEL with an iterative solving scheme is formulated for the pullout problem to solve the corresponding nonlinear differential equation of motion. Moreover, comparisons between the obtained results regarding the different proposed material models of the interface are provided. The elastic damage model can be used with a dynamical increasing factor (DIF) on the bond strength and the stiffness of the interface with respect to the shear slip rate. On the other hand, the developed viscoelastic damage material models characterize the rate-dependent effects of the dynamical pullout through the viscous and the viscoelastic parts of the corresponding constitutive relations of these models. The second part of this doctorial thesis deals with the mechanical analysis of the uniaxial tensile behavior of TRC specimen under dynamical tensile loading. A corresponding analytical model is firstly formulated. Furthermore, a tested TRC tensile specimen and the corresponding fiber crack bridging behavior (cracked stage) are also analyzed by means of the Finite Element modeling approach by conducting 3-dimensional heterogeneous models. / Textil bewehrter Beton (Textilbeton) ist ein neues Baumaterial mit zunehmender Verwendung in modernen Ingenieuranwendungen. Die experimentellen Untersuchen an Textilbeton zeigen Mehrfachrissbildung, die zu Betonriss- und Faserauszugsmechanismen korrespondieren. Das Ziel dieser Forschungsarbeit ist die mechanische Untersuchung des Faserauszugsmechanismus unter dynamischer Belastung. Hierzu werden geeignete Materialmodelle für das Matrix-Faser-Interface vorgeschlagen, die zwei mechanische Phänomene, nämlich das Schädigungsverhalten und den Dehnraten-Effekt, berücksichtigen. Diese Materialmodelle sind das elastische Schädigungsmodell, das viskoelastische Modell und zwei entwickelte viskoelastische Schädigungsmodelle. Zudem wird ein analytisches Modell zum Faserauszugsmechanismus bereitgestellt, wobei die beschreibende Bewegungsgleichung aufgestellt und geschlossene, analytische Lösungen unter dynamischer Erregung durch eine harmonische Auszugsverschiebung am Faserende gefunden werden. Diese analytischen Lösungen werden für zwei Materialmodelle, das elastische Schädigungsmodell und das viskoelastische Modell, hergeleitet. Außerdem wird die dynamische Antwort für den Fall einer linear ansteigenden Auszugsverschiebung mit konstanter Geschwindigkeit gesucht. Zu dieser dynamischen Belastung wurde für die numerische Lösung der entsprechenden nichtlinearen Differentialgleichung ein diskretesModell (DISCRETE MODEL) entwickelt und mit einem iterativen Lösungsverfahren gelöst. Darüber hinaus wurde ein Vergleich zwischen den Ergebnissen, die bei Verwendung der unterschiedlichen vorgeschlagenen Materialgesetze für das Interface erhalten wurden, durchgeführt. Das elastische Schädigungsmodell kann zum einen mit einem von der Schlupfrate abhängigen dynamischen Vergrößerungsfaktor (DIF) für die Verbundfestigkeit bzw. die Steifigkeit des Interface verwendet werden. Zum anderen werden die Dehnraten-Effekte durch die viskosen und viskoelastischen Anteile in den entwickelten viskoelastischen Schädigungsmodellen abgebildet. Der zweite Teil dieser Dissertation behandelt die mechanische Untersuchung des uniaxialen Zugverhaltens von Textilbeton unter dynamischer Zugbelastung. Ein zugehöriges analytisches Modell wird zuerst formuliert. Zudem werden der Mehrfachrissbildungszustand und der Faserrissüberbrückungsmechanismus an einem Textilbetonprobekörper mittels einer Finite-Elemente-Analyse an einem dreidimensionalen, heterogenen Modell untersucht.

Textile reinforcement concrete (TRC) is a new building material in increasing usage in modern engineering applications. The experimental investigations of TRC reveal a multiple cracking behavior which corresponds to concrete cracking and fiber pullout mechanisms. The aim of the presented research work is the mechanical analysis of the fiber pullout mechanism under dynamical loading conditions. Appropriate constitutive material models are proposed for the matrix-fiber interface taking into consideration two main mechanical characteristics, damage behavior and rate-dependent effects. These material models are the elastic damage model, the viscoelastic model and two developed viscoelastic damage material models. Moreover, an analytical model of the fiber pullout mechanism is provided, where the governing differential equation of motion is formulated and closed analytical solutions are derived under a dynamical excitation of a harmonic pullout displacement function at the fiber tip. These analytical solutions are derived for two material models of the interface, the elastic damage and the viscoelastic material models. Furthermore, the dynamical responses are also sought for the case of a linearly increasing pullout displacement function of a definite velocity. For the latter dynamical loads a numerical DISCRETE MODEL with an iterative solving scheme is formulated for the pullout problem to solve the corresponding nonlinear differential equation of motion. Moreover, comparisons between the obtained results regarding the different proposed material models of the interface are provided. The elastic damage model can be used with a dynamical increasing factor (DIF) on the bond strength and the stiffness of the interface with respect to the shear slip rate. On the other hand, the developed viscoelastic damage material models characterize the rate-dependent effects of the dynamical pullout through the viscous and the viscoelastic parts of the corresponding constitutive relations of these models. The second part of this doctorial thesis deals with the mechanical analysis of the uniaxial tensile behavior of TRC specimen under dynamical tensile loading. A corresponding analytical model is firstly formulated. Furthermore, a tested TRC tensile specimen and the corresponding fiber crack bridging behavior (cracked stage) are also analyzed by means of the Finite Element modeling approach by conducting 3-dimensional heterogeneous models. / Textil bewehrter Beton (Textilbeton) ist ein neues Baumaterial mit zunehmender Verwendung in modernen Ingenieuranwendungen. Die experimentellen Untersuchen an Textilbeton zeigen Mehrfachrissbildung, die zu Betonriss- und Faserauszugsmechanismen korrespondieren. Das Ziel dieser Forschungsarbeit ist die mechanische Untersuchung des Faserauszugsmechanismus unter dynamischer Belastung. Hierzu werden geeignete Materialmodelle für das Matrix-Faser-Interface vorgeschlagen, die zwei mechanische Phänomene, nämlich das Schädigungsverhalten und den Dehnraten-Effekt, berücksichtigen. Diese Materialmodelle sind das elastische Schädigungsmodell, das viskoelastische Modell und zwei entwickelte viskoelastische Schädigungsmodelle. Zudem wird ein analytisches Modell zum Faserauszugsmechanismus bereitgestellt, wobei die beschreibende Bewegungsgleichung aufgestellt und geschlossene, analytische Lösungen unter dynamischer Erregung durch eine harmonische Auszugsverschiebung am Faserende gefunden werden. Diese analytischen Lösungen werden für zwei Materialmodelle, das elastische Schädigungsmodell und das viskoelastische Modell, hergeleitet. Außerdem wird die dynamische Antwort für den Fall einer linear ansteigenden Auszugsverschiebung mit konstanter Geschwindigkeit gesucht. Zu dieser dynamischen Belastung wurde für die numerische Lösung der entsprechenden nichtlinearen Differentialgleichung ein diskretesModell (DISCRETE MODEL) entwickelt und mit einem iterativen Lösungsverfahren gelöst. Darüber hinaus wurde ein Vergleich zwischen den Ergebnissen, die bei Verwendung der unterschiedlichen vorgeschlagenen Materialgesetze für das Interface erhalten wurden, durchgeführt. Das elastische Schädigungsmodell kann zum einen mit einem von der Schlupfrate abhängigen dynamischen Vergrößerungsfaktor (DIF) für die Verbundfestigkeit bzw. die Steifigkeit des Interface verwendet werden. Zum anderen werden die Dehnraten-Effekte durch die viskosen und viskoelastischen Anteile in den entwickelten viskoelastischen Schädigungsmodellen abgebildet. Der zweite Teil dieser Dissertation behandelt die mechanische Untersuchung des uniaxialen Zugverhaltens von Textilbeton unter dynamischer Zugbelastung. Ein zugehöriges analytisches Modell wird zuerst formuliert. Zudem werden der Mehrfachrissbildungszustand und der Faserrissüberbrückungsmechanismus an einem Textilbetonprobekörper mittels einer Finite-Elemente-Analyse an einem dreidimensionalen, heterogenen Modell untersucht.

When subjected to a combination of moment and shear force, a reinforced concrete (RC) beam with either little or no transverse reinforcement can fail in shear before reaching its full flexural strength. This type of failure is sudden in nature and usually disastrous because it does not give sufficient warning prior to collapse. To prevent this type of shear failure, reinforced concrete beams are traditionally reinforced with stirrups. However, the use of stirrups is not always cost effective since it increases labor costs, and can make casting concrete difficult in situations where closely-spaced stirrups are required. The use of steel fiber reinforced concrete (SFRC) could be considered as a potential alternative to the use of traditional shear reinforcement. Concrete is very weak and brittle in tension, SFRC transforms this behaviour and improves the diagonal tension capacity of concrete and thus can result in significant enhancements in shear capacity. However, one of the drawbacks associated with SFRC is that the addition of fibers to a regular concrete mix can cause problems in workability. The use of self-consolidating concrete (SCC) is an innovative solution to this problem and can result in improved workability when fibers are added to the mix. The thesis presents the experimental results from tests on twelve slender self-consolidating fiber reinforced concrete (SCFRC) beams tested under four-point loading. The results demonstrate the combined use of SCC and steel fibers can improve the shear resistance of reinforced concrete beams, enhance crack control and can promote flexural ductility. Despite extensive research, there is a lack of accurate and reliable design guidelines for the use of SFRC in beams. This study presents a rational model which can accurately predict the shear resistance of steel fiber reinforced concrete beams. The thesis also proposes a safe and reliable equation which can be used for the shear design of SFRC beams.

When subjected to a combination of moment and shear force, a reinforced concrete (RC) beam with either little or no transverse reinforcement can fail in shear before reaching its full flexural strength. This type of failure is sudden in nature and usually disastrous because it does not give sufficient warning prior to collapse. To prevent this type of shear failure, reinforced concrete beams are traditionally reinforced with stirrups. However, the use of stirrups is not always cost effective since it increases labor costs, and can make casting concrete difficult in situations where closely-spaced stirrups are required. The use of steel fiber reinforced concrete (SFRC) could be considered as a potential alternative to the use of traditional shear reinforcement. Concrete is very weak and brittle in tension, SFRC transforms this behaviour and improves the diagonal tension capacity of concrete and thus can result in significant enhancements in shear capacity. However, one of the drawbacks associated with SFRC is that the addition of fibers to a regular concrete mix can cause problems in workability. The use of self-consolidating concrete (SCC) is an innovative solution to this problem and can result in improved workability when fibers are added to the mix. The thesis presents the experimental results from tests on twelve slender self-consolidating fiber reinforced concrete (SCFRC) beams tested under four-point loading. The results demonstrate the combined use of SCC and steel fibers can improve the shear resistance of reinforced concrete beams, enhance crack control and can promote flexural ductility. Despite extensive research, there is a lack of accurate and reliable design guidelines for the use of SFRC in beams. This study presents a rational model which can accurately predict the shear resistance of steel fiber reinforced concrete beams. The thesis also proposes a safe and reliable equation which can be used for the shear design of SFRC beams.

When subjected to a combination of moment and shear force, a reinforced concrete (RC) beam with either little or no transverse reinforcement can fail in shear before reaching its full flexural strength. This type of failure is sudden in nature and usually disastrous because it does not give sufficient warning prior to collapse. To prevent this type of shear failure, reinforced concrete beams are traditionally reinforced with stirrups. However, the use of stirrups is not always cost effective since it increases labor costs, and can make casting concrete difficult in situations where closely-spaced stirrups are required. The use of steel fiber reinforced concrete (SFRC) could be considered as a potential alternative to the use of traditional shear reinforcement. Concrete is very weak and brittle in tension, SFRC transforms this behaviour and improves the diagonal tension capacity of concrete and thus can result in significant enhancements in shear capacity. However, one of the drawbacks associated with SFRC is that the addition of fibers to a regular concrete mix can cause problems in workability. The use of self-consolidating concrete (SCC) is an innovative solution to this problem and can result in improved workability when fibers are added to the mix. The thesis presents the experimental results from tests on twelve slender self-consolidating fiber reinforced concrete (SCFRC) beams tested under four-point loading. The results demonstrate the combined use of SCC and steel fibers can improve the shear resistance of reinforced concrete beams, enhance crack control and can promote flexural ductility. Despite extensive research, there is a lack of accurate and reliable design guidelines for the use of SFRC in beams. This study presents a rational model which can accurately predict the shear resistance of steel fiber reinforced concrete beams. The thesis also proposes a safe and reliable equation which can be used for the shear design of SFRC beams.