Une des manières d'augmenter la stabilité thermique de polymères consiste à leur ajouter de faibles quantités d'argile dispersées dans échelle nanométrique. De tels matériaux sont appelés de " nanocomposites ". Il existe plusieurs explications à ce phénomène, comme les effets de barrière de diffusion et la formation de charbon. D'autres sont en cours de vérification, comme les effets de piégeage de radicaux par les ions qui participent à des réactions de type Fenton. Notre objectif a été de suivre in situ des transformations chimiques de la phase argile, afin de mieux comprendre comment ces nanostructures lamellaires retardent la décomposition de polymères. Pour ce faire, trois types de nanocomposites ont été préparés: i) Poly(méthylméthacrylate)-co-Poly(trimetoxysilil propyl méthacrylate) et argiles montmorillonite (MMT) du type Cloisite (PMMA-co-PTMSM-Cloisite); ii) PMMA-argiles montmorillonites naturelles contenant différents taux d'ions Fe3+ dans les couches octaédrique (PMMA-MMT); iii) PMMA-hydroxydes doubles lamellaires (HDL), avec différentes proportions d' ions Zn2+ , Cu2+ et Fe3+ PMMA-HDL. La thermo-décomposition des argiles primitives et de leurs nanocomposites ont été suivies par des analyses thermiques, de diffusion de rayons X (SAXS et WAXS) et par spectroscopie d'absorption de rayons X (EXAFS). Les effets de l'atmosphère, de la composition chimique des lamelles, et de la quantité d'argile employée dans l'obtention des nanocomposites ont été évalués. L'étude des nanocomposites, PMMA-co-PTMSM-Cloisite a mis en évidence deux mécanismes de stabilisation. Elle a montré que l'addition d'argiles résulte en une stabilisation plus importante sous atmosphère d'air, que sous atmosphère de N2, et est aussi plus importante selon la quantité d'argile dispersée dans le polymère. La formation de charbon a aussi été observée seulement sous l'atmosphère d'air. La stabilité thermique des nanocomposites PMMA-MMT est aussi proportionnelle à la quantité d'argile employée dans l'obtention de la nanocomposite. Pour de faibles quantités d'argile, 0.3-1 % en masse, la stabilité thermique des nanocomposites est proportionnelle à la quantité de ions Fe3+ présents dans l'argile. Le suivi de l'environnement chimique des ions Fe3+ par EXAFS en fonction de la température, a montré que quand la phase argile est dispersée dans le PMMA, les ions Fe3+ sont réduits à Fe2+, ce qui ne se vérifie dans les phases primitives. Ces mécanismes de stabilisation indiquent que la phase argile stabilise le PMMA par des mécanismes de barrière de diffusion et par le piégeage des radicaux. Les nanocomposites PMMA-HDL contenant des ions Fe3+ sont plus stables que ceux qui contiennent des ions Cu2+. L'étude in situ de 'évolution de l'ordre local à moyenne distance en fonction de la température a montré que les phases HDL stabilisent le PMMA également par les mécanismes de barrière de diffusion et le piégeage de radicaux. L'ion Cu2+, induisant des distorsions dans l'ordre local, rend les lamelles moins stables : elles se décomposent à des températures inférieures, et l'effet de barrière de diffusion est alors réduit. Par contre, les ions Cu2+ et Fe3+ piègent des radicaux de la phase polymérique qui se décomposent et ralentissent le phénomène. Cette thèse démontre que les argiles peuvent agir comme des particules réactives ou inertes, c'est-à-dire, à travers des réactions chimiques avec le polymère ou comme barrière physique. La stabilisation thermique des polymères dépend d'une combinaison de mécanismes, parmi eux la barrière de diffusion, la formation de charbon et le piégeage de radicaux.

ABSTRACT EFFECTS OF VERTICAL EXCITATION ON SEISMIC PERFORMANCE OF HIGHWAY BRIDGES AND HOLD-DOWN DEVICE REQUIREMENT Domani&ccedil / , Kemal Arman M.S., Department of Civil Engineering Supervisor: Assist. Prof. Dr. Alp Caner February 2008, 152 pages Most bridge specifications ignore the contribution of vertical motion in earthquake analyses. However, vertical excitation can develop significant damage, especially at bearing locations as indeed was the case in the recent 1999 izmit Earthquake. These observations, combined with recent developments in the same direction, supplied the motivation to investigate the effects of vertical component of strong ground motion on standard highway bridges in this study. Reliability checks of hold-down device requirements per AASHTO Bridge Specifications have been conducted in this context. Six spectrum compatible accelerograms were generated and time history analyses were performed to observe the uplift at bearings. Selected case studies included precast pre-stressed I-girders with concrete slab, composite steel I-girders, post-tensioned concrete box section, and composite double steel box section. According to AASHTO specifications, hold-down devices were required in two cases, for which actual forces obtained from time history analyses have been compared with those suggested per AASHTO. The only non-linearity introduced to the analyses was at the bearing level. A discussion of effects on substructure response as well as compressive bearing forces resulting from vertical excitation is also included. The results of the study confirmed that the provisions of AASHTO governing hold-down devices are essential and reasonably accurate. On the other hand, they might be interpreted as well to be suggesting that vertical ground motion components could also be included in the load combinations supplied by AASHTO, especially to be able to estimate pier axial forces and cap beam moments accurately under combined vertical and horizontal excitations.

In this study influences of vertical ground motion on seismically isolated bridges were investigated for seven different earthquake data. One assessment of bearing effect involves the calculation of vertical earthquake load on the seismically isolated bridges. This paper investigates the influence of vertical earthquake excitation on the response of briefly steel girder composite bridges (SCB) with and without seismic isolation through specifically selected earthquakes. In detail, the bridge is composed of 30m long three spans, concrete double piers at each axis supported by mat foundations with pile systems. At both end of the spans there exists concrete abutments to support superstructure of the bridge. SCBs which were seismically isolated with nine commonly preferred different lead&amp / #8208 / rubber bearings (LRB) under each steel girder were analyzed. Then, the comparisons were made with a SCB without seismic isolation. Initially, a preliminary design was made and reasonable sections for the bridge have been obtained. As a result of this, the steel girder bridge sections were checked with AASHTO provisions and analytical model was updated accordingly. Earthquake records were thought as the main loading sources. Hence both cases were exposed to tri&amp / #8208 / axial earthquake loads in order to understand the effects under such circumstances. Seven near fault earthquake data were selected by considering possession of directivity. Several runs using the chosen earthquakes were performed in order to be able to derive satisfactory comparisons between different types of isolators. Analytical calculations were conducted using well known structural analysis software (SAS) SAP2000. Nonlinear time history analysis was performed using the analytical model of the bridge with and without seismic isolation. Response data collected from SAS was used to determine the vertical load on the piers and middle span midspan moment on the steel girders due to the vertical and horizontal component of excitation. Comparisons dealing with the effects of horizontal only and horizontal plus vertical earthquake loads were introduced.

Current seismic design approach of bridge structures can be categorized into two distinctive methods: (i) force based and (ii) performance based. AASHTO LRFD seismic design specification is a typical example of force based design approach especially used in Turkey. Three different importance categories are presented as &ldquo / Critical Bridges&rdquo / , &ldquo / Essential Bridges&rdquo / and &ldquo / Other Bridges&rdquo / in AASHTO LRFD. These classifications are mainly based on the serviceability requirement of bridges after a design earthquake. The bridge&rsquo / s overall performance during a given seismic event cannot be clearly described. Serviceability requirements specified for a given importance category are assumed to be assured by using different response modification factors. Although response modification factor is directly related with strength provided to resisting column, it might be correlated with selected performance levels including different engineering response measures. Within the scope of this study, 27216 single circular bridge column bent models designed according to AASHTO LRFD and having varying column aspect ratio, column diameter, axial load ratio, response modification factor and elastic design spectrum data are investigated through a series of analyses such as response spectrum analysis and push-over analysis. Three performance levels such as &ldquo / Fully Functional&rdquo / , &ldquo / Operational&rdquo / and &ldquo / Delayed Operational&rdquo / are defined in which their criteria are selected in terms of column drift measure corresponding to several damage states obtained from column tests. Using the results of analyses, performance categorization of single bridge column bents is conducted. Seismic responses of investigated cases are identified with several measures such as capacity over inelastic demand displacement and response modification factor.

Long span bridges are susceptible to wind. Hence it is important to study their wind-induced vibrations to avoid any probable structural failures. In this thesis, the results of an experimental and computational investigation of the aerodynamic characteristics of trapezoid bridge deck cross-sections with three different aspect ratios (10, 12 and 15) and four different side angles (75&ordm / , 60 &ordm / , 45 &ordm / and 30 &ordm / ) are analyzed and presented. The flow around rigid fixed bridge deck models is investigated to obtain the relevant aerodynamic coefficients and the vortex shedding frequency and Strouhal number. Two dimensional unsteady Reynolds Averaged Navier-Stokes equations are solved using commercial CFD software at different Reynolds numbers. The numerical results are compared with the experimental data obtained by testing the model bridge decks geometries in a low speed wind tunnel. The results of this study demonstrate that the models aerodynamic parameters except their lift coefficient are almost dependent on the aspect ratio. In addition, the influence of side angle on all aerodynamic parameters has to be taken in account.

Infrastructure systems are crucial facilities. They supply the necessary transportation, water and energy utilities for the public. However, while aging, these systems gradually deteriorate in time and approach the end of their lifespans. As a result, they require periodic maintenance and repair in order to function and be reliable throughout their lifetimes. Bridge infrastructure is an essential part of the transportation infrastructure. Bridge management systems (BMSs), used to monitor the condition and safety of the bridges in a bridge infrastructure, have evolved considerably in the past decades. The aim of BMSs is to use the resources in an optimal manner keeping the bridges out of risk of failure. The BMSs use the lifetime performance curves to predict the future condition of the bridge elements or bridges. The most widely implemented condition-based performance prediction and maintenance optimization model is the Markov Decision Process-based models (MDP). The importance of the Markov Decision Process-based model is that it defines the time-variant deterioration using the Markov Transition Probability Matrix and performs the lifetime cost optimization by finding the optimum maintenance policy. In this study, the Markov decision process-based model is examined and a computer program to find the optimal policy with discounted life-cycle cost is developed. The other performance prediction model investigated in this study is a probabilistic Bi-linear model which takes into account the uncertainties for the deterioration process and the application of maintenance actions by the use of random variables. As part of the study, in order to further analyze and develop the Bi-linear model, a Latin Hypercube Sampling-based (LHS) simulation program is also developed and integrated into the main computational algorithm which can produce condition, safety, and life-cycle cost profiles for bridge members with and without maintenance actions. Furthermore, a polynomial-based condition prediction is also examined as an alternative performance prediction model. This model is obtained from condition rating data by applying regression analysis. Regression-based performance curves are regenerated using the Latin Hypercube sampling method. Finally, the results from the Markov chain-based performance prediction are compared with Simulation-based Bi-linear prediction and the derivation of the transition probability matrix from simulated regression based condition profile is introduced as a newly developed approach. It has been observed that the results obtained from the Markov chain-based average condition rating profiles match well with those obtained from Simulation-based mean condition rating profiles. The result suggests that the Simulation-based condition prediction model may be considered as a potential model in future BMSs.

Die vorliegende Arbeit befasst sich mit experimentellen Untersuchungen zur physikalisch-chemischen und strukturellen Charakterisierung von neuartigen supramolekularen Kristalleinschlussverbindungen am Beispiel der Clathrate der Wirtverbindung 2,2’-bis(9-hydroxy-9-fluorenyl)biphenyl mit Aceton (polar) sowie Chloroform (unpolar). Durch die Kombination von Röntgenstrukturanalysen mit systematischen Messungen thermodynamischer Größen wie Löslichkeit, Einschluss-, Zersetzungs-, Lösungs- und Kristallisationsenthalpien konnten neue Erkenntnisse bezüglich der Struktur-Eigenschaftsbeziehungen sowie zur Rolle der Wirt-Gast Wechselwirkungen in den existierenden Einschlussverbindungen abgeleitet werden. Die Einschlussbildung bzw. Kristallisation verläuft für alle untersuchten Clathratphasen exotherm. Dies bedeutet, dass die Einschlussverbindungen gegenüber dem reinem Wirt energetisch stark begünstigt sind. Der bestimmende Beitrag hierfür resultiert aus der Bildung eines optimal gepackten Kristallgitters, während spezifische Wirt-Gast Wechselwirkungen nur eine untergeordnete Rolle spielen. Das Zersetzungsverhalten der verschiedenen Clathratphasen kann widerspruchsfrei aus der Packungsstruktur der Kristalle erklärt werden.

Data Centers (DCs) have become an intrinsic element of emerging technologies such as big data, artificial intelligence, cloud services; all of which entails interconnected and sophisticated computing and storage resources. Recent studies of conventional data center networks (DCNs) revealed two key challenges: a biased distribution of inter-rack traffic and unidentified flow classes: delay sensitive mice flows (MFs) and throughput-hungry elephant flows (EFs). Unfortunately, existing DCN topologies support only uniform distribution of capacities, provide limited bandwidth flexibilities and lacks of efficient flow classification mechanism. Fortunately, wireless DCs can leverage wireless communication emerging technologies, such as multi-terabit free-space optic (FSO), to provide flexible and reconfigurable DCN topologies. It is worth noting that indoor FSO links are less vulnerable to outdoor FSO channel impairments. Consequently, indoor FSO links are more robust and can offer high bandwidths with long stability, which can further be enhanced with wavelength division multiplexing (WDM) methods. In this thesis, we alleviate the bandwidth inefficiency by FSO links that have the desired agility by allocating the transmission powers to adapt link capacity for dynamically changing traffic conditions, and to reduce the maintenance costs and overhead. While routing the two classes along the same path causes unpleasant consequences, the DC researchers proposed traffic management solutions to treat them separately. However, the solutions either suffer from packet reordering and high queuing delay, or lack of accurate visibility and estimation on end-to-end path status. Alternatively, we leverage WDM to design elastic network topologies (i.e., part of the wavelengths are assigned to route MFs and the remaining for EFs). Since bandwidth demands can be lower than available capacity of WDM channels, we use traffic grooming to aggregate multiple flows into a larger flow and to enhance the link utilization. On the other hand, to reap the benefits of the proposed WDM isolated topology, an accurate and fast EF detection mechanism is necessary. Accordingly, we propose a scheme that uses TCP communication behavior and collect indicative packets for its flow classification algorithm, it demonstrates perfect flow classification accuracy, and is in order of magnitudes faster than existing solutions with low communication and computation overhead.

Content: The thermal degradation kinetics of hides before and after being tanned with formaldehyde were investigated using thermalgravimetric analysis (TGA) at four different heating rates of 5, 10, 20, 30 K/min. Such model-free methods as Flynn-Wall-Ozawa and Friedman as well as model-fitting method of Criado were employed to determine the thermal degradation active energy and degradation mechanism. Based on the Flynn-Wall-Ozawa and Friedman methods, the average active energy (Ea) of formaldehyde-tanned leather was 223.1 kJ/mol and 230.7 kJ/mol respectively. Results from general master curves showed diffusion processes in the thermal degradation of formaldehyde-tanned leather. Neither the thermal degradation activation energy nor the degradation mechanism is affected by the formaldehyde tanning. Nevertheless, the results by thermalgravimetric analyzer coupled with Fourier transform infrared spectrometry (TG-FTIR) indicated difference in the relative amounts of evolved products. According to the 3D-FTIR analysis, the dominant components of evolved gas for both untanned and tanned hides are CO2, CH4, H2O, NH3 along with small amount of HNCO. However, after formaldehyde tanning, both the evolved NH3 by the decomposition of free –NH2 groups and peptide –NH– groups from different amino acids in collagen and CH4 by the cleavage of -CH3 and -CH2- increase. Take-Away: 1. The theraml degradtion mechanism of hides before and after formaldehyde-tanning is eatablished in our paper. 2. The main degradation pathway of hides before and after formaldehyde-tanning is discussed with the help of TG-FTIR analysis.

The work deals with the preparation and study of polyphosphate composites. Aluminum phosphates provide some unusual properties like high-heat resistance in terms of inorganic binders. The addition of chromium in the form of Cr2O3 or directly the bond with the aluminum-chromium-phosphate can improve the properties of this binder. Highly viscous Al2Cr(H2PO4)9 and Al3Cr(H2PO4)12 binders were prepared by dissolving Al(OH)3 and CrO3 in 85% phosphoric acid, and mixed with Al2O3 and Cr2O3 fillers. The composites were cured in the furnace at 150 °C for 24 h under pressure of 10 MPa. During the annealing at temperatures up to 1 500 °C changes in chemical structure of the cured composites were observed, leading to the understanding of the creation of crystalline phases and their eventual changes. The characterization of binders was mainly based on FT-IR, EDAX, TG-DTA and optical microscopy analyses.