In the dissertation are analyzing the main characteristics of asphalt concrete influencing shear deformation, appearance and increase of rutting connected with them, analyze the influence of geosynthetic material characteristics onto asphalt concrete functioning.

High performance cementitious composites have been increasingly used for a range of structural applications in many countries. More recently, a notable interest has been focused on structural performance under seismic loading. However, a critical lack of coherent information and experimental/numerical data available in the literature has to be recognized along with the absence of specific and well-accepted code-guidelines for use of FRC in seismic applications. More specifically, when dealing with seismic resistant frame systems, few researchers have investigated in the past the seismic response of beam-column joints reinforced with steel fibres. These preliminary experimental tests have shown that adding steel fibres in joints is an effective method for improving joint behaviour and energy absorption capacity as well as enhancing the damage tolerance of joints and reducing the number of stirrups in seismic joints. However, due to the limited number of experimental tests as well as of the wide dispersion in the type and mechanical properties of the fibres adopted in these independent researches, the actual contributions of concrete, steel fibres and stirrups to the overall joint shear capacity has not yet been clearly identified and understood. This research aims to investigate the seismic behaviour and failure modes of beam-column joint subassemblies reinforced with steel fibres with the intent to provide preliminary suggestions for a simple but rational analytical procedure to evaluate the joint shear strength when either fibres and/or stirrups are adopted. As part of a more comprehensive on-going research campaign on the seismic behaviour of FRC members and systems, six 2-D exterior beam-column joint subassemblies were tested under simulated seismic loading (quasi-static cyclic loading regime) at the Civil Engineering Laboratory of the University of Canterbury. In order to assess the contribution of steel fibres to the joint (panel zone) shear strength, both under-designed systems (with no transverse reinforcement in the joint, following older practice before the pre-1970s) and well designed systems (following the NZ concrete design standard NZS 3101:1995) were adopted as benchmark specimens. The performance of steel fibre reinforced beam-column joints were compared with that of conventional joints. Results showed that using steel fibre reinforced concrete (SFRC) within beam-column joints can significantly enhance the shear resistance capacity of joints. However, using steel fibre reinforcement alone can not prevent buckling of the reinforcing bars when joints are under high intensity seismic loading. Furthermore, the test results also showed that using steel fibre reinforcement is an effective method to reduce the lateral reinforcement in the beam plastic hinge region. As part of the analytical investigation, a simplified procedure to evaluate the joint shear contribution provided by different amounts of fibres with or without the presence of stirrups has been also introduced. Influence of the axial load on the joint nominal shear capacity has been accounted for by adopting principle stresses. Tentative strength degradation curves (principle tensile stress vs. shear deformation) have also been calibrated on the experimental data which confirmed that a tentative relationship between the joint shear contributions provided by concrete, stirrups and steel fibres was a viable tool for designing SFRC joint. Furthermore, joint shear resistance coefficient contributed by steel fibres has been compared with previous experimental test available in literature to obtain an appropriate value for SFRC joint design guidelines. M_N performance based domain visualization has also been used to evaluate the hierarchy of strength and sequence of events of beam-column joint subassemblies.

Les travaux présentés dans cette thèse sont consacrés à l'enrichissement de la méthode de modélisation par éléments finis de type poutre multifibre. La méthode a fait ses preuves pour le calcul dynamique d'éléments de structures élancés, lorsque les contraintes normales prédominent. Toutefois, lorsque les contraintes de cisaillement sont prépondérantes, l'approximation de la cinématique utilisée par les éléments poutre n'est plus assez précise pour obtenir des résultats satisfaisants. L'objet de ces travaux de thèse est d'améliorer la méthode en créant un nouvel élément permettant de tenir compte du gauchissement des sections transversales dû au cisaillement. Ce développement est réalisé en deux étapes. Les éléments sont enrichis dans un premier temps par les déformations de gauchissement sous sollicitation de torsion. Le modèle de gauchissement est validé dans le domaine linéaire par confrontation aux résultats d'une modélisation numérique 3D. Après implémentation du gauchissement de torsion dans l'élément multifibre, des simulations numériques de poutres en torsion pure sont comparées à des résultats d'essais, permettant de valider le comportement des éléments poutre dans les domaines linéaire et non linéaire. Un modèle d'endommagement est utilisé pour le béton, et le gauchissement est mis à jour au fur et à mesure du calcul en tenant compte de l'évolution des propriétés matériau. L'étape suivante d'enrichissement est alors réalisée, avec l'élaboration d'un modèle de gauchissement complet sous toutes sollicitations de cisaillement, couplé au modèle d'endommagement. Une validation locale du profil de gauchissement élastique sous effort tranchant est effectuée par comparaison à la solution analytique, puis le profil de gauchissement sous sollicitations couplées de torsion et d'effort tranchant est validé par confrontation aux résultats d'une modélisation 3D. Outre la prise en compte du cisaillement par effort tranchant, la principale différence de cet enrichissement avec le modèle précédent est le calcul implicite du profil de gauchissement de la poutre au cours du calcul de structure. Les deux modèles développés sont comparés sur le comportement de poutres en torsion monotone, afin de quantifier l'impact de la méthode de calcul sur la précision des résultats et sur l'efficacité du calcul. Finalement, le modèle complet avec gauchissement est appliqué à la simulation sismique d'une structure. L'ensemble de ces cas-tests montre que l'enrichissement de la méthode par éléments finis multifibres est fonctionnel, avec des perspectives d'amélioration en ce qui concerne l'efficacité numérique notamment, et des perspectives intéressantes d'application. / The 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.

<p> A microscopic study of two samples of the Gowganda Formation, both having undergone pure shear deformation at greenschist f acies metamorphism has shown: Sample A -Reduction in quartz grain size, and pressure solution shadows were evidence for strong pressure solution activity. Pre-lithification fractures provided channelways for the removal of quartz and water out of the system. Matrix quartz was not recrystallized. Sample B -Extensive local recrystallization of quartz due to pressure solution activity caused metamorphic segregation and the formation of a cleavage. Cleavage behaviour differs in the matrix from that observed in an area of contact strain, as produced by a buckled quartz vein. There is no evidence for removal of quartz from the system. </p> <p> A comparison between the two samples suggests that (a) water, in this case at least, is necessary to produce metamorphic segregation, (b) the system has to be closed to reach metamorphic segregation and (c) original features may be preserved through limited metamorphism if the rock is dried out early in its history. </p> / Thesis / Bachelor of Science (BSc)

Curved beams such as arches find ubiquitous applications in civil, mechanical and aerospace engineering, e.g., stiffened floors, fuselage, railway compartments, and wind turbine blades. The analysis of free vibrations of curved structures plays a critical role in their design to avoid transient loads with dominant frequencies close to their natural frequencies. One way to increase their areas of applications and possibly make them lighter without sacrificing strength is to make them of Functionally Graded Materials (FGMs) that are composites with continuously varying material properties in one or more directions. In this thesis, we study free vibrations of FGM circular beams by using a logarithmic shear deformation theory that incorporates through-the-thickness logarithmic variation of the circumferential displacement, and does not require a shear correction factor. The radial displacement of a point is assumed to depend only upon its angular position. Thus the beam theory can be regarded as a generalization of the Timoshenko beam theory. Equations governing transient deformations of the beam are derived by using Hamilton's principle. Assuming a time harmonic variation of the displacements, and by utilizing the generalized differential quadrature method (GDQM) the free vibration problem is reduced to solving an algebraic eigenvalue problem whose solution provides frequencies and the corresponding mode shapes. Results are presented for different spatial variations of the material properties, boundary conditions, and the aspect ratio. It is found that the radial and the circumferential gradation of material properties maintains their natural frequency within that of the homogeneous beam comprised of a constituent of the FGM beam. Furthermore, keeping every other variable fixed, the change in the beam opening angle results in very close frequencies of the first two modes of vibration, a phenomenon usually called mode transition. / Master of Science / Curved and straight beams of various cross-sections are one of the simplest and most fundamental structural elements that have been extensively studied because of their ubiquitous applications in civil, mechanical, biomedical and aerospace engineering. Many attempts have been made to enhance their material properties and designs for applications in harsh environments and reduce weight. One way of accomplishing this is to combine layerwise two or more distinct materials and take advantage of their directional properties. It results in a lightweight structure having overall specific strength superior to that of its constituents. Another possibility is to have volume fractions of two or more constituents gradually vary throughout the structure for enhancing its performance under anticipated applications. Functionally graded materials (FGMs) are a class of composites whose properties gradually vary along one or more space directions. In this thesis, we have numerically studied free vibrations of FGM circular beams to enhance their application domain and possibly use them for energy harvesting.

Fiber-reinforced polymeric (FRP) composites are being considered for structural members in bridge construction as lighter, more durable alternatives to steel and concrete. Extensive testing and analysis of a pultruded, hybrid double web beam (DWB) developed for use in bridge construction has been conducted at Virginia Tech. A primary purpose of this testing is the development of a structural design guide for the DWB, which includes stiffness and strength data. The design manual also includes design allowables determined through a statistical analysis of test data. Static testing of the beams, including failure tests, has been conducted in order to determine such beam properties as bending modulus, shear stiffness, failure mode, and ultimate capacity. Measuring and calculating the shear stiffness has proven to be an area of particular interest and difficulty. Shear stiffness is calculated using Timoshenko beam theory which combines the shear stiffness and shear area together along with a shear correction factor, k, which accounts for the nonuniform distribution of shear stress/strain through the cross-section of a structure. There are several methods for determining shear stiffness, kGA, in the laboratory, including a direct method and a multi-span slope method. Herein lays the difficulty as it has been found that varying methods produces significantly different results. One of the objectives of current research is to determine reasons for the differences in results, to identify which method is most accurate in determining kGA, and also to examine other parameters affecting the determination of kGA that may further aid the understanding of this property. This document will outline the development of the design guide, the philosophy for the selection of allowables and review and discuss the challenges of interpreting laboratory data to develop a complete understanding of shear effects in large FRP structural members. / Master of Science

The study experimentally examines the quasi-static shear deformation of a magnetorheological (MR) fluid structured in an external magnetic field. Experiments are carried out using a rheometer with a plate–plate configuration. The working surfaces of the measuring geometry are modified to demonstrate their influence on the response of the field-structured MR fluid. The simplest possible suspension of microparticles of carbonyl iron in mineral oil without using surfactants or any modifiers is used. The difference in results obtained for structured MR fluid with different concentrations of magnetic particles using different modifications of the surface is demonstrated. The results are intended to motivate more intensive research on the issue and further more in-depth theoretical analysis of static elastic properties of structured MR fluids. Certain related critical issues are briefly highlighted.

Fiber reinforced polymeric (FRP) composite materials are beginning to find use in construction and infrastructure applications. Composite members may potentially provide more durable replacements for steel and concrete in primary and secondary bridge structures, but the experience with composites in these applications is minimal. Recently, however, a number of groups in the United States have constructed short-span traffic bridges utilizing FRP members. These demonstration cases will facilitate the development of design guidelines and durability data for FRP materials. The Tom's Creek Bridge rehabilitation is one such project that utilizes a hybrid FRP composite beam in an actual field application. This thesis details much of the experimental work conducted in conjunction with the Tom's Creek Bridge rehabilitation. All of the composite beams used in the rehabilitation were first proof tested in four-point bending. A mock-up of the bridge was then constructed in the laboratory using the actual FRP beams and timber decking. The mock-up was tested in several static loading schemes to evaluate the bridge response under HS20 loading. The lab testing indicated a deflection criterion of nearly L/200; the actual field structure was stiffer at L/450. This was attributed to the difference in boundary conditions for the girders and timber panels. Finally, the bridge response was verified with an analytical model that treats the bridge structure as a wood beam resting upon discrete elastic springs. The model permits both bending and torsional stiffness in the composite beams, as well as shear deformation. A parametric study was conducted utilizing this model and a mechanics of laminated beam theory to provide recommendations for alternate bridge designs and modified composite beam designs. / Master of Science

Approved for public release, distribution is unlimited / The effect of friction-stir processing (FSP) on the microstructure of a cast nickel-aluminum bronze (NAB) material has been characterized by various micro-analytical methods including orientation imaging microscopy (OIM). Cast NAB is widely utilized in the production of propellers for the surface ships and submarines of the U.S. Navy due to excellent corrosion-resistance. New applications require improved mechanical properties that may be attainable using FSP to achieve localized microstructure modification. Friction between a rotating tool and the surface of the material results in a *stirring* action that, in turn, produces adiabatic heating and local softening of the material. The tool rotation results in very large shear deformations in the softened regions and thus microstructure refinement and homogenization; in effect FSP may convert an as-cast microstructure to a wrought condition in the absence of macroscopic shape change. In as-cast material, results of optical and scanning electron microscopy (using energy dispersive analysis) show an ` (FCC) matrix containing globular and particulate dispersions that correspond to the *I, *II and *IV second phases; these represent various morphologies of the Fe3Al intermetallic compound, which has a D03 structure. Also present are lamellar particles of *III, which is NiAl and has a B2 structure. The grain size in the ` matrix is ~ 1 mm. In OIM, the microtexture and microstructure in the ` (FCC) matrix may be readily obtained and analyzed. However, interatom distances in the Fe3Al and NiAl phases differ by only about one percent and so these phases are not distinguishable from one another during OIM. Altogether, microstructure and microtexture analysis showed that there are several regions in the thermomechanically affected zone (TMAZ) of a material subjected to FSP. From base material inward toward the TMAZ, these include: annealing effects in undeformed base material; a region just inside the TMAZ in which grain deformation and C-type shear deformation textures are observed; regions of highly refined and recrystallized grains further inside the TMAZ, wherein the grain size is < 5æm; and, finally, regions of elongated, banded and twinned grain structures that suggest grain growth following recrystalliztion. / Lieutenant, United States Navy

Approved for public release, distribution is unlimited / The extreme strain, strain rate and temperature gradients during Friction Stir Processing (FSP) render measurement of key parameters in the stir zone infeasible with common methods. The objective of this research was to separate the effects that temperature and deformation in an experimental study of the microstructure and mechanical properties of Ni-AL bronze (NAB). This was accomplished by subjecting as-cast NAB material to several isothermal annealing and quenching treatments as well as isothermal hot rolling processes. Sufficient material was generated to provide results and data for subsequent optical microscopy, tensile, & hardness tests. All results were then compared to similar data collected from previous works completed here at Naval Postgraduate School and with other DARPA FSP program participants. During the course of this work correlations were drawn between FSP material and the material subjected to isothermal hotworking, which may enhance our understanding of the roles that various FSP process parameters have on the microstructural transformation sequence within this material. The hot-rolling study conducted here suggests that FSP process parameters leading to severe deformation at temperatures between 950-1000 C in the NAB material provides high ductility (elongation approximately 28%) with moderate strengths. / Lieutenant, United States Coast Guard