Highway bridges are considered to be one of the most susceptible constituents of transportation networks when they are subjected to severe natural hazards such as earthquakes and environmental exposures like subfreezing temperatures. To facilitate and enhance pre-hazard event mitigation and post-hazard emergency response strategies, probabilistic risk assessment methodologies have attracted increased attention, recently. Seismic fragility assessment is one of the probabilistic techniques which predicts the damage risk of the structure for a given hazard level. While fragility curves can be developed using different methods, such as expert-based, empirical, experimental, analytical, and hybrid, analytical fragility curves are perceived to be the most reliable and least biased technique. Seismic isolation systems are prevalently used in bridge structures to mitigate the damage risk of bridge components against natural hazards. However, the effectiveness of implementing recently emerged isolators such as Stable Unbonded Fiber Reinforced Elastomeric Isolators (SU-FREI) should be examined by developing analytical fragility curves of retrofitted bridges and quantifying the mitigation in the damage probability of different bridge components. In this regard, incorporating the Soil-Structure Interaction (SSI) is critical since the lateral response of bridges relies on the relative stiffness of bridge components, such as columns and isolators and the supporting soil. In addition, all bridge components are exposed to environmental stressors like subfreezing temperature that can alter the seismic response of bridges. In the first phase of this thesis, a seismic fragility assessment is carried out on an existing multi-span continuous reinforced concrete bridge. Two bridge representations are developed to simulate the as-built bridge along with its retrofitted counterpart utilizing SU-FREI. An Incremental Dynamic Analysis (IDA) is conducted using 45 synthetic ground motion records developed for eastern Canada and damage limit states are applied to generate fragility curves and determine the probability of damage to different bridge components. Bridges are analyzed in longitudinal and transverse directions, independently, and component- and system-level fragility curves are developed. In the second phase, the previously generated bridge models are expanded to incorporate the SSI effects by introducing the pile groups under piers and abutments. Several interactions including deck-abutment, abutment-embankment, pile-soil, and pile-soil-pile interactions are considered. A significant challenge in this phase is the accurate simulation of the lateral and vertical behavior of pile groups since all pile groups comprised of closely-spaced vertical and battered piles. A ground motion suite consisting of 45 ground motions has been selected, which reflects the seismicity of the bridge site. IDA is conducted to monitor the seismic performance of the bridge from the elastic linear region up to collapse. Fragility curves, which serve as an important decision-support tool have been developed to identify the potential seismic risk of the bridge. In the third phase, a multi-hazard assessment is carried out by conditioning the previously developed bridge models (i.e. monolithic fixed-base, isolated fixed-base, monolithic with SSI, and isolated with SSI) to a range of room and subfreezing temperatures and applying a seismic excitation, simultaneously. The cold temperature behavior of the constitutive materials of different bridge components, namely, concrete, reinforcing steel, rubber, and the supporting soil are studied and reflected in the bridge models. IDA is performed and damage potential of different bridge components are quantified. In summary, it is demonstrated that SU-FREI is a competing alternative for seismic isolation of bridges by offering potentially less manufacturing time and cost, lower weight, and easier installation which is an attractive feature for accelerated bridge construction applications. In all three phases, it is shown that the bridges which are isolated using SU-FREI have improved seismic performance in comparison with monolithic bridges by exhibiting lower probability of damage to the primary bridge components like columns and pile caps and transferring the damage to less important components such as abutments at which damage does not cause bridge closure. In addition, it is shown that seismic isolation using SU-FREI can effectively mitigate the seismic demand and damage potential of the constitutive components of a bridge supported by weak soil. While occurrence of seismic events along with an environmental stressor such as cold temperature can drastically jeopardize the functionality of a bridge supported by weak soil, it is demonstrated that seismic isolation using SU-FREI can significantly alleviate the probability of damage to bridge components. / Dissertation / Doctor of Philosophy (PhD)

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During strong ground motions, structures equipped with base isolation systems have been shown to have their seismic demand significantly reduced, mitigating adverse effects such as damage and loss of life. More recently, the fiber-reinforced elastomeric isolator (FREI) has been investigated as a relatively new type of isolator for the base isolation of structures. Constructed from alternating layers of elastomer and carbon-fiber cloth, FREI can be produced in large pads that can be cut to any desired size and shape when required. In bridges, FREI can to be used in an unbonded application (U-FREI) by placing them between the bridge deck and the piers. Experimental and numerical investigations have shown U-FREI as a viable option for the isolation of bridges. However, experimental studies have been limited to room temperature testing. In North America, climates vary drastically across the continent. Northern climates, such as those existent in Canada, are capable of reaching extremely low temperatures. Thus, base isolated bridges in these regions require isolation systems that perform adequately at cold temperatures. The studies presented in this dissertation have been completed in order to investigate the effects that low temperatures have on U-FREI used in bridge structures. An experimental program was conducted that evaluated the behaviour of U-FREI. It was found that U-FREI performed adequately under lateral displacements expected during a seismic event, and provided acceptable response under vertical and rotational testing that is typical of normal bridge operation. Using these results, a numerical model for U-FREI was then updated to account for the effects of low temperature. The model was combined with a bridge model to evaluate the seismic response of a bridge structure isolated with U-FREI subjected to low temperatures. A substantial reduction in seismic demand was achieved, even under the most severe conditions tested. / Thesis / Master of Applied Science (MASc)

In this dissertation, four distinct but in some ways related topics, mostly related to experimental and theoretical investigations of friction and adhesion of elastomeric materials, are presented. First, an experimental and theoretical study of the interaction between elastic beams and granular media under compressive loading is performed. Buckling loads of beams with different dimensions and boundary conditions within granular media of different depths and grain sizes are measured, and theoretically approximated using the Ritz energy approach, based on the concept of beam on an elastic foundation. Several nondimensional parameters and a scaling law are derived to characterize different interaction regimes between the beams and granular support. The findings from this work is believed to be helpful for improved understanding of interactions between elastic beams and surrounding elastic foundation with applications to piles, oil pipelines, and robotic needle insertion into soft tissues. Second, the role of axial compliance on the friction of extensible strips is investigated. Significant changes were observed in the static and kinetic friction of strips, when the effective axial compliance was changed. The underlying causes of the changes in the frictional response are explained and quantitatively predicted using an extended shear lag model. We believe that this study provides insights into the effect of axial compliance on the frictional response of materials, paving the way for design and optimization of systems where the static and kinetic friction forces play an important role. Third, the effect of normal force and rate on the kinetic friction of two different elastomers, namely acrylic and silicone-based elastomers is evaluated. A custom-built pendulum test setup was used to perform the friction test in dynamic conditions. Two substantially different responses with respect to the change in normal force were observed and the role of different contributions to the frictional response of viscoelastic materials, i.e. bulk hysteresis friction, adhesion friction, and cohesion friction, are discussed. Different scenarios such as modifying the surface by using graphite powder, reducing test velocity, and also performing drop tests to characterize the surface hysteresis of the elastomers, were considered to further explore the origin of frictional responses of the elastomers. This study could improve insights gained from Dynamic Mechanical Analysis (DMA) data when obtaining and interpreting the effect of normal force on kinetic COF of elastomers with potential applications to tires, shoes, etc. where friction plays an important role. Last, a generalized scaling law, based on the classical fracture mechanics approach, is developed to predict the bond strength of adhesive systems. The proposed scaling law, which depends on the rate of change of bond area with compliance, is in apparent discrepancy with the previously reported scaling relationship that depends on the ratio of area to compliance. This distinction can have a profound impact on the expected bond strength of systems, particularly when failure mechanism changes or the compliance of the load train is increased. Furthermore, the shear lag model is implemented to derive a closed-form relation for the system compliance and the conditions where the two models deviate from each other are discussed and demonstrated. The results obtained from this approach could lead to a better understanding of the relationship between the bond strength and the geometry and mechanical properties of adhesive systems, with applications to different types of adhesive joints such as bio-inspired adhesive, biomedical adhesive tapes, and structural adhesive joints. / Ph. D.

This study evaluates noise and vibrations in a heavy freight locomotive cab, and provides several measures for providing more comfort to the crew. A full-scale production cab and sill structure is used to provide the results. The cab is setup in a controlled laboratory environment in a manner similar to the installation on a locomotive. Field measurements are used to emulate actual vibration input to the cab structure. A 16-channel data acquisition system is used to collect both noise and vibration data on various parts of the cab structure and inside the cab. Upon establishing the baseline for laboratory vibration measurements and correlating them with field data, a design of experiment was conducted to evaluate the vibration contribution of various parts of the cab. This showed that the cab floor and cab roof had the largest vibrations. A series of solutions including stiffening the cab floor and damping the cab roof were investigated. The results showed that although such solutions reduce localized vibrations, the overall effect on reducing cab interior noise is minimal. As a more global solution, the cab was isolated from the sill structure through six elastomeric elements mounted at the base of the cab and at the crash post. The mounts at the base were selected such that they support the static weight of the cab, provide a resonance frequency that is below the excitation range, and offer good lateral and longitudinal stability. Two tube-form elastomeric mounts were placed between the cab structure and the crash posts which attach to the front of the sill structure. The test results showed that the soft-mounted cab had significantly lower noise and vibration than the original cab. The vibration levels were reduced 10 to 100 times at certain locations and frequency ranges. The overall noise level was reduced by approximately 6 dBA. In an attempt to provide an estimate of effectiveness of the mounts with different stiffness values, a simulation model was prepared in Matlab. Although the model did not yield accurate results, it resulted in several recommendations for future research work. / Master of Science

[pt] Arcos abatidos são usados com frequência para vencer grandes vãos. Exemplos incluem pontes em arco e coberturas de grandes espaços como galpões industriais e estádios. Em muitos casos empregam-se arcos atirantados ou apoiados em estruturas flexíveis, fazendo com que os apoios se movam quando o arco é carregado. Isto aumenta a flexibilidade do sistema e a probabilidade de perda de estabilidade na presença de cargas estáticas e dinâmicas. Em muitos casos estas estruturas podem ser modeladas como arcos com apoios elásticos. No presente trabalho resolve-se o problema de estabilidade estática de forma analítica e através de uma aproximação usando o método de Ritz, servindo a solução analítica para aferir a precisão do modelo numérico. A seguir, com base neste estudo, desenvolve-se, usando o método de Ritz, a formulação para análise das vibrações não lineares do arco com apoios elásticos, assunto inédito na literatura. Os resultados mostram a grande influência dos apoios nas vibrações não lineares e na estabilidade do arco sob cargas estáticas e dinâmicas. / [en] Shallow arches are often used to overcome large spans, for example, arch bridges or steel roofs to cover large spaces such as industrial sheds and stadiums. In many cases the arches are tied or are supported by a flexibility structure, causing that supports to move when the arch has been loaded. This increases the flexibility of the system and the probability of loss of stability in the presence of static and dynamic loads. In many cases, these structures can be modeled as arches with elastic supports. In the present work the static stability has been solved analytically and through the Ritz method, serving the analytical solution to assess the accuracy of the numerical model. Then, based on this study, the analysis of nonlinear vibrations of shallow arches with elastic supports is developed, using the Ritz method, a subject not yet studied in the literature. The results show the noticeable influence of the supports on the nonlinear vibration and stability of shallow arches under static and dynamic loads.

[pt] Dentro do campo dos controladores passivos, um dos dispositivos usados pelas suas propriedades de amortecimento são os Apoios Elásticos, que constituem uma solução econômica e efetiva na supressão ou atenuação das vibrações em sistemas dinâmicos com problemas de ressonância ou instabilidade, freqüentemente pela falta de amortecimento suficiente. Este trabalho envolve o estudo de um rotor horizontal com apoios elásticos (silicone), adaptado a partir de um rotor existente, o estudo de diversos efeitos sobre a sua operação, a medição de seu movimento, a identificação dos parâmetros do problema, a medição e validação a partir de resultados simulados em um modelo numérico. Os fenômenos incluídos no estudo são o efeito giroscópio (rotor descentrado com respeito do vão), desbalanceamento do rotor e empenamento do eixo. Neste trabalho os parâmetros do sistema foram determinados usando técnicas de identificação, análise modal e otimização não linear devido à anisotropia do sistema. / [en] Viscoelastic Passive Controllers are an important field of technological research due to the development of new materials and design techniques. Damping properties allow an easy retrofit of existing machines with excessive vibration problems, developing Elastomeric Bearing Supports. They are an economic and effective solution in the suppression or attenuation of vibrations in dynamic systems suffering from instability or resonance problems, which often lack of sufficient damping. This work involves the study of an horizontal rotor with elastomeric bearing supports, adapted of another one, the study of several effects on his operation, the measurement of his motion, the identification of the problems parameters, the measurement and validation from the simulated results in a numeric model. Phenomena included in the study are the gyroscopic effect (rotor out of the middle), rotor unbalance and shaft bow. In this work the systems parameters were determined using identification, modal analysis and nonlinear optimization techniques due to the anisotropy of the system.

Polymer networks are an important class of materials that are ubiquitously found in natural, biological, and man-made systems. The complex mesoscale structure of these soft materials has made it difficult for researchers to fully explore their properties. In this dissertation, we introduce a coarse-grained computational model for permanently cross-linked polymer networks than can properly capture common properties of these materials. We use this model to study several practical problems involving dry and solvated networks. Specifically, we analyze the permeability and diffusivity of polymer networks under mechanical deformations, we examine the release of encapsulated solutes from microgel capsules during volume transitions, and we explore the complex tribological behavior of elastomers. Our simulations reveal that the network transport properties are defined by the network porosity and by the degree of network anisotropy due to mechanical deformations. In particular, the permeability of mechanically deformed networks can be predicted based on the alignment of network filaments that is characterized by a second order orientation tensor. Moreover, our numerical calculations demonstrate that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. We show that swollen gel capsules allow steady, diffusive release of nanoparticles and polymer chains, whereas gel deswelling causes burst-like discharge of solutes driven by an outward flow of the solvent initially enclosed within a shrinking capsule. We further demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods in the capsule interior. We also probe the effects of velocity, temperature, and normal load on the sliding of elastomers on smooth and corrugated substrates. Our friction simulations predict a bell-shaped curve for the dependence of the friction coefficient on the sliding velocity. Our simulations also illustrate that at low sliding velocities, the friction decreases with an increase in the temperature. Overall, our findings improve the current understanding of the behavior of polymer networks in equilibrium and non-equilibrium conditions, which has important implications for synthesizing new drug delivery agents, designing tissue engineering systems, and developing novel methods for controlling the friction of elastomers.