In recent years, repetitive traumatic brain injuries have been linked to the progressive neurodegenerative disorder termed chronic traumatic encephalopathy. However, the mechanical characteristics of brain tissue exposed to repetitive loading still lack understanding. This research evaluated the response of porcine brain tissue undergoing cyclic, compressive loading in reference to three impact parameters: cycle number (N25, N50, N100, N150, and N200), strain level (15, 30, and 40%), and strain rate (0.00625, 0.025, 0.10, and 1.0/s). Following mechanical testing, tissue samples were processed for hematoxylin and eosin (H&E) staining. Stress values, hysteresis energy, and decreases in hysteresis energy for all parameters were compared. The data suggest that microstructural brain tissue damage is highly dependent on strain level and cycle number, whereas strain rate did not appear to cause permanent damage in the quasi-static range applied. The onset of permanent microstructural tissue damage may relate to movement of fluid molecules within the tissue.

No / This study explores the lateral deflections of diagonal braces in concentrically-braced earthquake-resisting frames. The performance of this widely-used system is often compromised by the flexural buckling of slender braces in compression. In addition to reducing the compressive resistance, buckling may also cause these members to undergo sizeable lateral deflections which could damage surrounding structural components. Different approaches have been used in the past to predict the mid-length lateral deflections of cyclically loaded steel braces based on their theoretical deformed geometry or by using experimental data. Expressions have been proposed relating the mid-length lateral deflection to the axial displacement ductility of the member. Recent experiments were conducted on hollow and concrete-filled circular hollow section (CHS) braces of different lengths under cyclic loading. Very slender, concrete-filled tubular braces exhibited a highly ductile response, undergoing large axial displacements prior to failure. The presence of concrete infill did not influence the magnitude of lateral deflection in relation to the axial displacement, but did increase the number of cycles endured and the maximum axial displacement achieved. The corresponding lateral deflections exceeded the deflections observed in the majority of the previous experiments that were considered. Consequently, predictive expressions from previous research did not accurately predict the mid-height lateral deflections of these CHS members. Mid-length lateral deflections were found to be influenced by the member non-dimensional slenderness ( ) and hence a new expression was proposed for the lateral deflection in terms of member slenderness and axial displacement ductility. / TATA Steel

The performance of connections and full-scale shear walls constructed with acrylic foam pressure sensitive adhesive (PSA) tape is the focus of this thesis. The objectives of this study were first to investigate the bonding characteristics of adhesive tape to wood substrates and then to expand this investigation to cover adhesive-based shear walls subjected to high wind and seismic loadings. A total of 287 monotonic connection tests and 23 reversed cyclic wall tests were performed to achieve these objectives. Connection tests were performed in accordance with ASTM D 1761-88 (2000), and walls were tested using the CUREE (Consortium of Universities for Earthquake Engineering) general displacement-based protocol. Variables investigated within the main study were the following: the use of OSB versus plywood sheathing, the effect of priming and surface sanding on adhesion, and the comparison of connections involving mechanical fasteners with those that utilized only adhesive tape or a combination of the two. It was found that an application pressure of 207 kPa (30 psi) or greater was needed to form a sound bond between the acrylic foam adhesive tape and a wood substrate. Properly bonded OSB and plywood connections provided fairly ductile failure modes. Full-scale walls constructed with adhesive tape performed similarly to traditional wall configurations, while walls constructed with a combination of adhesive tape and mechanical fasteners provided significant gains in strength and toughness. The results of this study serve to provide a foundation for expanding the engineering uses of acrylic foam adhesive tape for structural applications. / Master of Science

Post-tensioning (PT) strands have been employed in a number of self-centering seismic force resisting systems as part of the restoring force mechanism which virtually eliminates residual building drifts following seismic loading. As a result of the PT strands large elastic deformation capability, they have been proven to work efficiently in these types of systems. Although typically designed to stay elastic during design basis earthquake events, strands may experience inelastic cyclic loading during extreme earthquakes. Furthermore, the yielding and fracture behavior of PT strand systems is central to the collapse behavior of self-centering systems. The loading conditions to which PT strands are typically subjected in prestressed/post-tensioned concrete applications are vastly dissimilar, and only limited research has explored the behavior of PT strands as subjected to inelastic cyclic loading. The testing program conducted to characterize the behavior of PT strand systems as they might be applied in self-centering applications incorporated more than fifty tests, including monotonic and cyclic tests to failure. Variations in the test configuration included strand obtained from two manufacturers, single-use and multiple-use anchorage systems, and variations in initial post-tensioning strand stress. Characteristics of the response that were investigated included seating losses, deformation capacity prior to initial fracture, additional deformation capacity after initial fracture, and the overall load-deformation behavior. Data was analyzed to provide recommendations for PT strand system usage in self-centering seismic force resisting systems. It was concluded that significant strength and ductility allow PT strand systems to consistently provide self-centering systems with reliable restoring force capability. / Master of Science

The primary direction of this thesis was towards exploring qualitative and quantitative characteristics necessary for refining and understanding the flat wood double cantilever beam (DCB) as a valid means for testing Mode I fracture energy in wood adhesive bonds. Southern yellow pine (SYP) adherends were used with epoxy and phenol formaldehyde (PF) impregnated films, providing two systems with different characteristics for investigation. An adhesive penetration analysis was performed for both the epoxy and PF bonds. The PF penetration into the SYP was shown to be relatively shallow. The epoxy penetration was shown to be deeper. Epoxy-SYP DCBs were quasi-statically tested with varying widths (10 mm, 15 mm, and 20 mm), showing decreases in scatter of critical and arrest strain energy release rates, GIc and GIa, with increases in specimen width. Quasi-static fracture testing was also performed on PF SYP-DCBs, showing much higher critical and arrest fracture energy values than the epoxy-SYP DCBs, indicating that deep adhesive penetration is not necessarily a requisite for higher Mode I fracture energy values. Grain distribution influences were computationally investigated because of the stiffness difference between latewood and earlywood growth and the grain angle along the length of the beams. The grain angle and the stiffness difference between latewood and earlywood growth caused the effective stiffness, (ExxI)eff, to vary along the length of the beam. The effective stiffness variation caused variations in the beam's ability to receive and store strain energy, complicating and confounding determination of experimental results. Cyclic loading tests were performed on PF-SYP DCB's. The cycle frequency was 3Hz, with a valley to peak load ratio of R = 0.5. Specimen softening was observed with cycling, with re-stiffening occurring with crack growth. Contrary to expectations, specimen compliance occasionally decreased with small crack extensions. A toughening mechanism was frequently observed, whereby subsequent crack lengths required more cycles to failure than the previous crack length. Monotonically extending the crack length far from the fatigued region created a fresh crack that did not show the toughened behavior. But toughening did resume with subsequent crack lengths. / Master of Science

This thesis presents the results of testing to determine if spacing between bolts in a multiple-bolt, single-shear connection subjected to natural hazard loading affects seven strength and serviceability parameters: maximum load, failure load, E.E.P. yield load, 5% offset load, elastic stiffness, E.E.P. energy, and ductility ratio. This research also determines if a statistical difference exists between previously published research for 4D spacing as compared to results produced by this research for five alternate spacings: 8D, 7D, 6D, 5D, and 3D. Finally, this research determines which of the spacings examined: 8D, 7D, 6D, 5D, 3D; produced the most optimal results for each examined strength and serviceability parameter where optimization is based on economy and performance. Three connection configurations with five different spacings between bolts were subjected to reverse cyclic loading for a total of one hundred and fifty tests. The reverse cyclic protocol was based on recommendations by the Consortium of Universities for Research in Earthquake Engineering (CUREE) for testing woodframe structures. The same connection configurations were also subjected to monotonic loading for an additional forty-five tests. Results of this research can be used to evaluate the current design recommendation presented in the National Design Specification (NDS) for Wood Construction (AF&PA, 2001) of spacing bolts at four times the bolt diameter (4D) to determine if a different spacing should be recommended for natural hazard loading conditions. / Master of Science

Yes / The performance of buried rigid pipes underneath geogrid-reinforced soil while applying incrementally increased cyclic loading was assessed using a fully instrumented laboratory rig. The influence of varying two parameters of practical importance was investigated; the pipe burial depth and the number of geogrid-layers. Measurements were taken for pipe deformation, footing settlement, strain in pipe and reinforcing layers, and pressure/soil stress on the pipe crown during various stages of cyclic loading. The research outcomes demonstrated a rapid increase in the rate of deformation of the pipe and the footing, and the rate of generated strain in the pipe and the geogrid-layers during the first 300 cycles. While applying further cycles, those rates were significantly decreased. Increasing the pipe burial depth and number of geogrid-layers resulted in reductions in the footing and the pipe deformations, the pressure on pipe crown, and the pipe strains. Redistribution of stresses, due to the inclusion of reinforcing layers, formed a confined zone surrounding the pipe providing it with additional lateral support. The pipe invert experienced a rebound, which was found to be dependent on pressure around the pipe and the degree of densification of the bedding layer. Data for strains measured in the geogrid-layers showed that despite the applied loading value and the pipe burial depth, the tensile strain in the lower geogrid-layer was usually higher than that measured in the upper layer.

La mise en place de trains à grande vitesse a rendu de plus en plus cruciale la compréhension et la prévision du comportement dynamique à long terme des voies ferrées. En particulier, le tassement des infrastructures conditionne le coût de maintenance des voies. Ce tassement d’infrastructure est par ailleurs étroitement lié aux propriétés des matériaux constitutifs sollicités par le chargement cyclique. La thèse décrit les résultats obtenus pour la caractérisation d’un matériau de type « micro-ballast » de constitution semblable à celle d’un ballast utilisé en infrastructure ferroviaire, mais de taille de grain réduite (d/D=6/24). L’expérimentation utilise des appareils triaxiaux de deux diamètres F300mm et F100 mm. 1. Essais sous sollicitation monotone: Les essais poussés jusqu’à rupture ont permis de mettre en évidence une courbure de la courbe intrinsèque sous faible niveau de chargement et un effet d’échelle sensible entre les deux tailles d’échantillon. 2. Essais sous chargement cyclique: Le plan d’expériences a permis de prendre en compte l’influence de la fréquence d’application de la sollicitation cyclique, de la pression de confinement, de la charge appliquée et du nombre de cycles. Les résultats obtenus sont interprétés dans le cadre d’une loi de comportement adaptée à l’étude de sollicitations cycliques à grand nombre de cycles / The use of high-speed trains makes it crucial to understand and predict the long term dynamic behavior of railway tracks. In particular, the settlement of infrastructures incurs track maintenance costs. This settlement of infrastructure is besides closely linked to the physical properties of the material, when stressed by a cyclic loading. The thesis describes the experimental results obtained on a so called « micro-ballast » material whose grain properties are similar to those of a ballast used for train tracks, but having reduced grain size (d/D=6/24) . Experiments are performed by using triaxial testing on tow diameters (300 mm and 100 mm). 1. Tests under monotone compression: failure tests provided evidence for a curvature of the failure envelop and a significant scale effect between both sample sizes. 2. Tests under cyclic loading: The experimental plane took into account the influence of the application frequency used for the cyclic loading, the confining pressure, the applied charge and the number of cycles. An interpretation of the results in the context of constitutive equations which can be used for the simulation of a high number of cycles is presented

Ce travail porte sur la caractérisation, par une méthode acoustique, du comportement mécanique d’un milieu granulaire sous chargement cyclique. La propagation d’ondes ultrasonores, à travers le réseau des contacts supportant les efforts dans l’échantillon, permet de sonder les propriétés viscoélastiques de ces milieux hétérogènes. Dans une première partie, nous étudions le comportement visco-élasto-plastique d’un empilement de billes de verre lors d’un essai oedométrique. Nous examinons en particulier le tassement, ou la déformation résiduelle, et la dissipation hystérétique, en fonction du nombre de cycles, du taux de déformation et de l’état de surface des billes. Nous montrons que les modules déduits des donnés mécaniques (déformation e ~ 10?4-10?³) sont dix fois plus petits que ceux obtenus par les mesures acoustiques (e ~ 10?7) à cause de la réponse non linéaire du milieu. Dans une seconde partie, nous nous intéressons au fluage et à la relaxation de contrainte du milieu. L’originalité de cette étude est le suivi par la mesure de la vitesse du son, qui présente une augmentation de type logarithmique dans les deux types d’essais. Le modèle basé sur la mécanique des microcontacts entre grains rugueux décrit bien nos résultats expérimentaux / This work deals with the characterization, by an acoustical method, of the mechanical behaviour of a dry dense granular medium under cyclic loading using an acoustic technique. The sound propagation through the contact-force network supporting the external load offers a non-invasive probe of the viscoelastic properties of such heterogeneous media. First, we study the visco-elasto-plastic response of the glass bead packing during an oedometric test and investigate the settlement or residual deformation and the hysteretic dissipation as function of loading cycles, strain rate and the surface state of the grains. We show that the modulus deduced from mechanical results (strain e ~ 10?4-10?³)) are about tens time smaller than those from acoustic measurements (e ~ 10?7) due to the nonlinear response of the material. Next, we examine creep and relaxation phenomena of the granular medium. The novelty of our study lies in the simultaneous monitoring of the sample using acoustic measurements. We find quasi-logarithmic increase of sound velocities in both mechanical tests. The model based on the mechanics of micro-contact between rough grains describes fairly well our experimental results

L'objet de ce travail de recherche est d'étudier le comportement mécanique de structures multi-matériaux d'un point de vue empirique et théorique. Ces structures mixtes s'articulent autour de plusieurs matériaux : le bois, le béton, les résines et les armatures. Le but est de tirer avantage de chaque matériau pour améliorer le comportement général de la structure tant au niveau de la résistance ultime que de la rigidité. De nouvelles méthodes de liaison sont également étudiées pour proposer de nouvelles solutions constructives innovantes dans le domaine du Génie Civil. La première partie de ce travail est consacrée à l'étude des liaisons bois-béton. Ainsi une analyse expérimentale est menée à l'aide d'essais push out pour déterminer les meilleures configurations permettant la connexion des matériaux bois et béton. Ces essais push out ont permis de caractériser les joints collées bois-béton sous différentes configurations et ont également permis de retenir deux systèmes constructifs : une par voie sèche et une par voie humide. La seconde étape consiste à tester ces méthodes de fabrication à grande échelle. Une campagne expérimentale sur des poutres de 8 m de long et des planchers de 8,15 m a donc débuté. Des essais de flexion 4 points en chargement quasi statique ont permis de caractériser le comportement mécanique de onze configurations de poutres. Les résultats confirment l'intérêt des sections hybrides dans la construction : gain de capacité portante et gain de rigidité. Le collage et le nouveau système de liaison sont donc des systèmes performants qui évitent tout glissement entre les matériaux. Les tests sur plancher montrent que comparer aux charges classiques en bâtiment, les panneaux ont une marge de sécurité vis-à-vis de l'état limite de service et de l'état limite ultime. La dernière étape se concentre sur l'étude d'un chargement cyclique des panneaux hybrides. Un essai de flexion 4 points est utilisé pour solliciter pendant un million de cycles les planchers entre 4 et 20 kN. Ces charges correspondent respectivement à un plancher déchargé avec le poids mort du carrelage, cloisons et faux-plafond et un plancher chargé avec des charges d'exploitation de bureaux. Après les essais cycliques, un test de résistance résiduelle est également effectué. En parallèle, une étude analytique pour modéliser le comportement mécanique instantané des structures hybrides est effectuée. Ce modèle analytique se base sur un calcul itératif en étudiant les déformations de la section et en équilibrant les forces internes. Le comportement mécanique de chaque matériau est pris en compte et notamment leur non-linéarité. Ce modèle développé en chargement statique a également été adapté pour prendre en considération le fluage des matériaux et ainsi obtenir le comportement différé des structures bois-béton / The objective of this project is to develop composite structures. These kinds of structures are made with wood, concrete, adhesive and rebar. The purpose is to take advantages of each material in order to improve the mechanical behavior of the hybrid structure. New bonding systems are proposed and studied to offer innovating solutions in Civil Engineering.The first part is dedicated to the study of the liaison between wood and concrete by gluing. An experimental analysis is done with push out tests in order to determine the best configurations to connect wood and concrete. Two constructive methods have been retained: a dry way and a humid way.The second step consists to test these methods of fabrication in real condition. An experimental campaign on beams and panels is launched with 4 points bending tests and under static loading to characterize the mechanical behavior of eleven beams. The interest of such hybrid sections is confirmed: gain of the bearing capacity and rigidity. The gluing and the new system of bonding are both performing and avoid slip between materials. Tests on panels show a security margin compared to classic loads in construction, for both limit states.The last stage of the thesis focuses on the study of cyclic loading of hybrid panels where 4 points bending test is used to load panels for one million cycles between 4 and 20 kN. These loads correspond respectively to the dead load on the unloaded panels and the panels loaded with regulatory live loads. After cyclic tests are performed, a bending test to the rupture is conducted.In parallel, an analytical study to model the instantaneous mechanical behavior of composite structure is proposed. This model is based on an iterative calculation by studying the deformation of the section and by equilibrating internal forces. The mechanical behavior of each material is takes into account with their non-linearity. This modelling is developed for static loads and was adapted to take in consideration creep of materials and thus obtain the differential behavior of wood-concrete structures