Based on the definition given in the AASHTO LRFD Bridge Design Specifications, twin steel box-girder bridges are classified as bridges with fracture critical members (FCMs), in which a failure of a tension member is expected to lead to a collapse of the bridge. However, a number of such bridges with either a partial or full-depth crack in one girder have been reported and are still providing service without collapsing. The main objective of this research project is to understand the behavior of twin steel box-girder bridges and to develop methods for evaluating their redundancy level in the event of the fracture of one tension member. The research project included an experimental investigation on a small-scale steel twin box-girder bridge, field testing of a full-scale twin box-girder, analysis of existing research and design data, and an extensive amount of numerical analyses carried out on calibrated 3-D nonlinear finite element models. The results from this study provide in-depth understanding of twin steel box-girder bridge behavior before and after a fracture in the tension member occurs. In addition to the experimentally verified finite element method, the report also proposes simplified methods for evaluating the load-carrying capacity of twin steel box-girder bridges under vii concentrated loads and provides a list of important factors that could control the reserve capacity of the damaged bridge. The main conclusion of this research is that the redundancy exists in twin steel boxgirder bridges in an event that a fracture of a tension member(s) takes place. This research project also provides a comprehensive roadmap for assessing the redundancy of twin steel box-girder bridges in which the elements of the roadmap are identified, and solutions for several of the steps are provided. The development of solutions for remaining steps of the roadmap is proposed for a future research.

L'objet de cette thèse vise à montrer expérimentalement l'amplification dans le domaine terahertz d'échantillons à base de puits quantiques en nitrure de gallium (GaN), maintenus à basses températures (< 100 K), grâce au mécanisme physique de "résonance du temps de transit des phonons optiques". Po ur ce faire, un banc expérimental permettant de mesurer le spectre en transmission des échantillons dans différentes gammes de fréquences (0.220-0.325, 0.843-1.100 et 0.7-1.7 THz suivant la source utilisée), et sous différentes conditions (température, orientation, champ électrique appliqué) a été développé. Un deuxième banc, servant à mesurer les caractéristiques courant-tension en régime continu ou pulsé a également été réalisé en vue de l'étude électrique des composants à basses températures. Les résultats montrent l'existence d'un effet conséquent sur le spectre de transmission au fur et à mesure que le champ électrique appliqué augmente. / The objective of this thesis is to experimentally demonstrate the amplification in the terahertz frequency domain by quantum wells of gallium nitride (GaN), maintained at low temperatures (< 100 K), thanks to the so called "optical phonon transit time resonance" mechanism. To achieve that goal, an experimental setup have been developed to measure the transmission spectra of the samples under study in different frequency bands (0.220-0.325, 0.843-1.100, and 0.7-1.7 THz depending on the source), and under different experimental conditions (temperature, orientation, applied electric field). Besides this first setup, another bench have been developed to measure the DC and pulsed current-voltage characteristics at low temperatures. The results show a significant enhancement on the transmission spectra as the applied electric field is increased.

Public support for the US Supreme Court has been trending downward for more than a decade. High-profile decisions and hotly contested nominations have drawn the Court into our polarized politics. Recently, some justices have spent considerable time and energy giving interviews, speeches, and the like, assuring the public that the Court is an apolitical, neutral arbiter of disputes, distinct from the "political"branches. In this context, we turn to an understudied potential source of judicial legitimacy: The off-bench public rhetoric of Supreme Court justices. In this article, we present evidence from three original survey experiments to argue that Supreme Court justices' off-bench rhetoric can powerfully influence public perceptions of the Court's institutional legitimacy. Furthermore, these studies show that performance approval is key to changes in legitimacy: Respondents who disapprove of a Court decision were immune to the effects of justices' rhetoric.

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Yes / This paper presents the experimental results of axial compression tests on concrete-filled bimetallic tubes (CFBT). The cross section of the bimetallic tube is composed of an outer layer made of stainless steel and an inner layer made of carbon steel. A total of 12 specimens with a circular cross section were tested under axial compression. The test parameters included the thickness of the stainless steel tube layer (tss=0-1.36 mm) and the compressive strength of the infilled concrete (fcu=21.1-42.8 MPa). Test results showed that, the two layers of the bimetallic tube worked well together, and the CFBT specimens exhibited ductile characteristics. The influence of the parameters on the failure mode, load versus deformation relationship, axial compressive strength, and strain development of the tested specimens were investigated. Finally, the feasibility of three existing design codes for predicting the axial compressive strength of CFST under axial compression was evaluated. / Tsinghua University Initiative Scientific Research Program, China Postdoctoral Science Foundation

O problema das vibrações induzidas por vórtices em cilindros flexíveis inclinados em relação ao perfil de correnteza incidente é estudado através de uma abordagem experimental. Este tema se mostra de grande importância e aplicação na Engenharia Naval e Oceânica uma vez que são diversas as estruturas que se encaixam nesta descrição, como são o casos dos risers e linhas de amarração. Apesar de extensa, a literatura técnica especializada no assunto é focada em simplificações, tais como os estudos de cilindros rígidos fixos, cilindros rígidos montados em base elástica e cilindros flexíveis verticais ou lançados em catenária livre. A questão da inclinação é abordada em termos do Principio da Independência que diz que as forças e a frequência de emissão de vórtices em um cilindro inclinado são iguais as de um cilindro vertical se considerada apenas a parcela da correnteza normal à direção de inclinação. Estudos anteriores mostraram que este princípio é válido somente em algumas condições específicas e poucos deles apresentam resultados para cilindros flexíveis. Com base nisso, um ensaio em escala reduzida em tanque de reboque foi realizado com um modelo de linha composto por um tubo de silicone preenchido com microesferas de aço e condições de contorno articuladas em suas extremidades, o que conferiu características inerciais e geométricas ideais para a obtenção do fenômeno. Além da configuração vertical (? = 0°), que é o caso de referência, o modelo foi estudado em outras quatro inclinações com a vertical: ? = 10°, 20°, 30° e 45°. Estas inclinações foram ensaiadas para cinco diferentes azimute: ? = 0°, 45°, 90°, 135° e 180°, resultando em vinte e uma configurações de inclinação. Os resultados são analisados em termos da decomposição modal da vibração da linha, ou seja, são apresentadas amplitudes e frequências de oscilação ocorridas em cada um dos modos de vibrar. Além disso são realizadas análises espectrais, gráficos de evolução espaço-temporal, trajetórias de pontos ao longo do modelo flexível, entre outros. Frequências naturais, coeficientes de amortecimento e trações no topo são apresentados, complementarmente, como resultados de caracterização do modelo. Os estudos apontaram para uma validade do PI com algumas ressalvas, principalmente influenciadas pela diferença nas frequências do primeiro e segundo modo que é crescente com o aumento da inclinação. Além disso conclusões importantes sobre a coexistência modal, em regiões de ressonância e/ou de transição da dominância modal, foram obtidas. / The vortex-induced vibration problem in flexible cylinders yawed in relation to the incident current profile is studied through an experimental approach. This topic has great importance and application on Naval and Oceanic Engineering once there are multiple structures that fit into this description, such as risers and mooring lines. Though extensive, technical literature specialized on this topic is focused on simplifications such as the study of fixed rigid cylinders, elastic base rigid cylinders and flexible cylinders assembled vertically or launched in free hanging catenary. The inclination issue is addressed in the terms of the Principle of Independence which states that the forces and frequency shedding in an inclined cylinder are equal to those of a vertical cylinder if only considered the current component normal to the inclination plane. Previous studies showed that this principle is valid only on some specific conditions and few of them showed results to flexible systems. Based on this, a scaled tow tank test was performed with a line model composed of a silicone tube filled with steel microspheres and articulated end conditions, which offered the ideal inertial and geometrical conditions to obtaining the phenomenon. Besides the vertical configuration (? = 0°), which is the reference case, the model was studied in other four inclinations with the vertical: ? = 10°,20°, 30° and 45°. These inclinations were tested for five different azimuth directions: ? = 0°, 45°, 90°, 135° and 180°, resulting in 21 configurations. The results are analyzed on terms of the modal decomposition of the line motions, that is, amplitudes and oscillation frequencies are presented for each one of the vibration modes. Furthermore other analyzes are made, as spectral graphs, spatio-temporal evolution graphs, line points trajectories, among others. Natural frequencies, damping coefficients and tensions at the top are presented, complementarly, as results of the model characterization. The studies pointed to a validity of the IP with some reservations, mainly influenced by the difference in of the first and second mode frequencies that is increasing with the yaw increase. In addition, important conclusions about modal coexistence in regions of resonance and / or transition of modal dominance were obtained.