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<p>Structural walls in existing buildings designed to pre 1970s codes may have deficient shear reinforcement and lap splice detailing. Lap splices at the bottom of the walls were designed in compression with anchorage length of 24-bar diameter. When the structural wall is subjected to lateral loads during a major seismic event, the lap splice is in the zone of maximum moment and shear and may be subjected to tension. Such design may cause nonductile behaviour and sudden failure of the wall due to shear or bond slip of the lap splice reinforcing bars. The effect of shear and ductility rehabilitation on the behaviour of reinforced concrete structural walls, without lap splice, have shown improvement in the structural wall shear resistance and ductility and hence overall structural ductility and seismic loads resistance. Research on rehabilitation of reinforced concrete (RC) structural walls with both deficient shear reinforcement and lap splice detailing is still needed. </p> <p> The principal objectives of this study were to evaluate the seismic behaviour of non-ductile reinforced concrete structural walls before and after rehabilitation using carbon fibre reinforced polymers (CFRP). These objectives were achieved through experimental and analytical investigations.</p> <p> The experimental phase of this research involved testing large scale models of RC structural walls with deficient shear strength and lap splice detailing to reproduce failure modes observed following major seismic events and to evaluate the rehabilitation schemes. Ten RC structural walls were built and tested under cyclic loading. Three control walls were tested as-built with non-ductile detailing and seven walls were rehabilitated before testing. The purpose of the rehabilitation techniques was to prevent brittle failure in shear or bond slip and to improve the ductility and energy dissipation of RC structural walls.</p> <p> The analytical phase of this study involved evaluation of the inelastic dynamic response of RC residential building with nonductile structural walls as well as retrofitted walls. An efficient macroscopic model to represent the behaviour of RC structural walls when subjected to pushover, cyclic and dynamic seismic loads was developed. The proposed model was intended to adequately describe the hysteretic behaviour of walls and to be capable of accurately predicting both flexural and shear components of inelastic deformation. The model predictions were compared with the experimental results. The comparisons showed that the developed analytical model predicted the inelastic walls response with a good accuracy. The analytical model was capable to evaluate the nonlinear dynamic behaviour of an existing building under seismic excitation before and after rehabilitation.</p> / Thesis / Doctor of Philosophy (PhD)

An investigation was undertaken to better understand the corrosion behaviour of dissimilar welded Cu-lean AA7003 and AA7108 extrusions. The major variables under study were the heat-treated condition (as-welded T6 vs. as-welded T6+Paint Bake (PB)), extrusion alloy Cu composition (AA7003 vs. AA7108), weld filler composition (ER4043 vs. ER5356), weld joint geometry (lap-joint vs. T-joint), and weld direction with respect to extrusion direction (parallel (═) vs. perpendicular (┴)). The corrosion behaviour of the various weld configurations under investigation was observed using an ASTM standard practice for modified salt spray testing (ASTM G85-A2), a GM worldwide engineering standard for cyclic corrosion testing (GMW-14872), and potentiodynamic polarization measurements. The effect of exposure to GMW-14872 on the tensile-shear behaviour of the various weld configurations under study was also investigated using a custom tensile jig. Examination post exposure to ASMT G85-A2 revealed the presence of differing pitting corrosion morphologies between AA7003 and AA7108. Due to increased Cu-content, AA7003 displayed deep pitting corrosion which penetrated the entirety of the dynamically recrystallized top surface layer and reached the fine-grained interior. Shallow pitting of the recrystallized surface layer was observed on AA7108, with very few penetration sites that reached the underlying fine-grained interior. No difference in corrosion behaviour was observed between the heat affected zone (HAZ) and unaffected base alloy of welded AA7003 and AA7108, also consistent with potentiodynamic polarization results. However, the HAZ displayed dual corrosion bands separated by a thin band of unattacked alloy; a result of distinct local microstructural changes induced by thermal cycling from welding. Tensile-shear testing revealed four types of observed fracture modes: shear across the weld throat, fracture along the AA7xxx/ER5356 interface, fracture along the AA6063/ER5356 interface and fracture in the HAZ of AA7xxx. Little to no corrosion was observed on weld configurations exposed to GMW-14872, resulting in no differences in the tensile-shear behaviour of exposed and unexposed weld configurations. Large variations observed in the tensile-shear results were a result of numerous weld defects. / Thesis / Master of Applied Science (MASc)

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No description available.

In motorsport, simulating road vehicles driving at the limit of handling is a valuable tool to study and optimize their overall performance during the design and set-up phases. Along with Quasi-Steady-State optimization, optimal control (OC) is the most utilized technique to simulate the control and states of a vehicle during minimum-time maneuvers and has been used for offline lap-time optimization for more than twenty years now. Since the first applications of optimal control in this field, it has been clear that the solution of the minimum-time optimization does not represent a model of the human driver but instead substitutes him/her. However, the common points or divergences between the minimum-time strategy of human race drivers and the OC one are still unclear. Moreover, it seems that in the literature there is no agreement about what vehicle models must be used, and in general the choice of one model or the other is not clearly justified. Finally, thanks to the rise in popularity of autonomous driving and racing, optimal control has been used as path planner for automated vehicles: %nonetheless, the application of free-trajectory real-time nonlinear optimal control in Model Predictive Control (MPC) schemes, where the optimal controls are directly fed to the vehicle, is still an unexplored topic. nonetheless, the application of free-trajectory real-time nonlinear optimal control in Model Predictive Control (MPC) schemes, where the optimal controls are computed from a single optimization and directly fed to the vehicle, is a topic still open for exploration. The first aim of this thesis is to provide an objective comparison of several vehicle, tire, powertrain and road models to be used in minimum-time OC. In the first part of this work we thus detail several models of the vehicle and its subsystems. We then solve minimum-time OC problems on a series of test tracks adopting most of the model combinations and discuss the differences in the solutions. We then draw conclusions on the best model combinations to obtain realistic and reliable minimum-time maneuvers. The second part of the thesis aims to prove that the solutions of minimum-time OC problems are indeed different from the driving behavior of professional drivers, but they can be employed to coach the human driver and improve his/her racing performance. After modeling a high-performance vehicle manufactured by Ferrari, we again use optimal control to compute minimum-time maneuvers on two different tracks. A professional racer driving is then coached in following the OC strategy on the Ferrari driving simulator, and we objectively prove that the driver can outperform his previous lap times. In the third and last part of the thesis, we aim to prove that free-trajectory real-time optimal control is a valid alternative to hierarchical MPC frameworks based on high-level path planning and low-level path tracing. We first develop a novel kineto-dynamic vehicle model able to satisfy the trade-off between computational lightness and accuracy in representing the vehicle's pure and combined dynamics. Then, by solving a minimum-time OC in real-time, we are able to autonomously drive a real scaled vehicle around a track at the limits of tire adherence.

It was the objective of this research to develop high temperature and high performance polyimides that also display (a) thermal stability; (b) crystallinity in the initial material and ability to crystallize from the melt; (c) fast crystallization kinetics and (d) melt processability. This unique combination of properties is presently unavailable in any other polyimide. In this regard, the present work investigates the crystallization, morphology and thermal stability of two novel semicrystalline polyimides based on the same diamine, 1,3-bis (4-aminophenoxy) benzene (TPER), but two different dianhydrides, 3,3',4',4'-biphenyltetracarboxylic dianhydride (BPDA) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). Phthalic anhydride was used as an endcapper to improve the thermal stability of the polyimides. The BPDA based polyimide was also tested extensively as a structural adhesive using Ti-6Al-4V coupons. Additionally, these polyimides are based on monomers, that are presently commercially available. The bulk thermal stability of the polyimides was first evaluated using dynamic and isothermal thermogravimetric experiments. DSC was utilized to test the ability of the polyimides to crystallize from the melt after exposures to varying melt times and temperatures. Exceptional thermal stability was demonstrated by BPDA based polyimide with no change in the melting behavior after 40 min at 430°C or 30 min at 440°C. The semicrystalline morphology of the material was studied using hot stage polarized optical microscopy (OM) and atomic force microscopy. The spherulitic growth rates were determined as a function of crystallization temperature after quenching from various melt times and temperatures. The effect of crystallization temperature, previous melt time and melt temperature on the morphology was considered. The spherulitic growth rates increased with increasing undercooling in the temperature range studied (nucleation controlled), while the growth rate at a specific crystallization temperature decreased on increasing the previous melt time and temperature. The melting behavior was studied after different crystallization times and temperatures and also as a function of different heating rates. Crystallization kinetics was followed both isothermally and non-isothermally using DSC and OM. Avrami analysis was performed for TPER-BPDA and the obtained results were correlated with microscopic observations. Melt viscosity measurements were carried out as a function of melt temperature, melt time and frequency. The adhesive investigations for TPER-BTDA utilized lap-shear test, wedge test and double cantilever beam tests. The durability of the adhesive and the fracture surface was studied after exposure to various solvents and after high aging and testing temperatures. The polyimide demonstrated very high average room temperature lap-shear strengths (8400 psi or 59 MPa), excellent solvent resistance and durability of strengths at high aging and testing temperatures. / Ph. D.

The tensile resistance of No. 15 lap spliced reinforcing bars with varying transverse spacing and lap splice length was evaluated in full-scale concrete block wall splice specimens. The range of the transverse spacing between bars was limited to that which allowed the bars to remain within the same cell, and included the evaluation of tied spliced bars in contact. Two-and-a-half block wide by three course tall double pullout specimens reinforced with contact lap splices were initially used to determine the range of lap splice length values to be tested in the wall splice specimens such that bond failure of the reinforcement occurred. The double pullout specimens were tested in direct tension with six replicates per arrangement. Three values of lap splice length: 150, 200, and 250 mm, were selected from the testing of the double pullout specimens and tested in the wall splice specimens in combination with three values of transverse spacing: 0, 25, and 50 mm, with three replicates per configuration. A total of twenty-seven two-and-a-half block wide by thirteen course tall wall splice specimens reinforced with two lap splices were tested in four-point loading. Both the double pullout and the wall splice specimens were constructed in running bond with all cells fully grouted. The tensile resistance of the lap spliced bars in the double pullout specimens was measured directly. The contact lap splices with a 150, 200, and 250 mm lap splice length developed approximately 38, 35 and 29% of the theoretical yield load of the reinforcement, respectively. The difference between the mean tensile resistances of the three reinforcement configurations tested in the double pullout specimens was found to be statistically significant at the 95% confidence level. Different than expected, the tensile resistance of the lap spliced reinforcing bars in the double pullout specimens was inversely proportional to the lap splice length provided. For the short lap splice lengths used in this investigation, the linear but not proportional relationship between bond force and lap splice length known from reinforced concrete is believed to have caused this phenomenon. An iterative sectional analysis using moment-curvature response was used to calculate the tensile resistance of the lap spliced reinforcement in the wall splice specimens. The calculated mean tensile resistance of the reinforcement increased with increasing lap splice length, and was greater when the bars were in contact. Securing the bars in contact may have influenced the tensile capacity of the contact lap splices as higher stresses are likely to develop as a result of the bar ribs riding over each other with increasing slip. Results of the data analysis suggest that the tensile resistance of non-contact lap splices within the same cell is generally independent of the spacing between the bars. A comparison of the experimental results for the wall splice specimens with the development and splice length provisions in CSA S304.1-04 and TMS 402-11 indicate that both the Canadian and U.S. design standards are appropriate for both contact and non-contact lap splices located within the same cell given the limited test database included in this investigation.

<p>Past earthquake damage assessments have shown the seismic vulnerability of older non-ductile reinforced concrete buildings. The life safety-risk these buildings pose has motivated researchers to study, develop, and improve modeling techniques to better simulate their behavior with the aim to prioritize retrofits.</p><p><br></p> <p>This study focuses on the lap splice detailing at the base of the building in columns, shorter than those recommended by modern codes which consider seismic effects. Current modeling efforts in non-ductile reinforced concrete frame structures have considered the connection at the foundation fixed. This study models the influence of the performance of short lap splices on the simulation of response of an instrumented perimeter-frame-non-ductile building located in Van Nuys, California, and to compare results with those of previous studies of the same building.</p><p><br></p> <p>The methodology consisted of evaluating the response of a non-ductile concrete building subjected to a suite of ground motions through the comparison of three base connections: fixed, pinned, and a rotational spring modeling the short lap splice. Comparison and performance evaluation are done on the basis of drift as the main performance metric. In the building response evaluation flexure and shear forces in frame elements were also compared using the different base conditions. </p><p><br></p> <p>The models consist of two-dimensional frames in orthogonal direction, including interior and exterior frames, totaling into 4 frames. The dynamic analysis was performed using SAP2000 analysis software. The proposed rotational spring at the base was defined using the Harajli & Mabsout (2002) bond stress – slip relationship and moment – curvature sectional analysis, applied to 24d_b and 36d_b lap splices. Deformation considered flexure and slip. Adequacy of shear strength was checked prior to the analysis to verify that shear failure did not occur prior to either reaching first yield of the column reinforcement or splice capacity. </p><p><br></p> In this study, the response of the frames using the proposed rotational spring model was found to be between the fixed and pinned base conditions with regard to roof displacement and interstory drift ratio, also termed as story drift ratio. The behavior of the frames changed depending on the yielding of the longitudinal reinforcement, as depicted by the interstory drift ratio and displacement. The performance of the building frames also depended on the ground motion. The N-S and E-W direction frame computational models considered three and four earthquakes, respectively, totaling to 14 computational models per base condition. Three computational models out of the 14 with the proposed rotational spring base condition simulated recorded roof displacement results with accuracy. In the frame simulations where yielding of most of the column longitudinal bars was not calculated, the maximum interstory drift occurred in the upper stories, matching column damage observations during the event. The findings of the study showed that short lap splice increases the drift and displacement compared to the fixed base supporting its effect, i.e. the behavior of a non-ductile reinforced concrete case study building to an earthquake.

[pt] Os materiais compósitos foram desenvolvidos para substituir o uso de ligas metálicas em aplicações de alto desempenho, se tornando materiais muito utilizados devido a uma ampla combinação de propriedades mecânicas. O setor de oleodutos, com o passar dos anos, tem enfrentado problemas nas tubulações devido ao envelhecimento e deterioração causados, principalmente, pela corrosão. Para solucionar esses problemas, normalmente, são utilizados reparos convencionais feitos com materiais metálicos tendo a finalidade de substituir a parte danificada. Porém, esse processo é muito trabalhoso e o setor de oleodutos tem visto como alternativa o uso de materiais compósitos poliméricos reforçados com fibra como reparo. As principais vantagens em relação aos reparos convencionais são a alta relação resistência-peso, a baixa concentração de tensão e a fácil aplicação. Entretanto, muitos estudos já mostraram que quando expostos a ambientes agressivos como temperatura, umidade e radiação ultravioleta, os materiais compósitos podem se deteriorar, ou seja, perdem suas propriedades mecânicas. Com isso, é importante analisar o efeito desses ambientes com o intuito de prever o comportamento mecânico, a vida útil e as possíveis falhas do reparo de juntas coladas. Com a finalidade de entender o comportamento mecânico, a adesão e a vida útil da junta adesiva, o objetivo desse trabalho foi analisar o envelhecimento de reparos em uma atmosfera salina. Foram utilizadas juntas Double-Lap Shear – DLS de compósito polimérico reforçado com fibra de vidro sobre um substrato de aço. As juntas foram fabricadas com quatro tipos tratamentos superficiais diferentes: I) Sem Silano / lixamento manual; II) Sem Silano / máquina Monti; III) Com Silano / lixamento manual; IV) Com Silano / máquina Monti. Os reparos de juntas coladas foram analisados em relação aos efeitos de temperatura (35 graus C, 55 graus C e 70 graus C) e da exposição a ambientes de névoa salina por um tempo de envelhecimento de até 6830h. O efeito do envelhecimento e a variação das propriedades mecânicas foram avaliados pelo ensaio destrutivo DLS e foi utilizado o ensaio não destrutivo de ultrassom para detectar o tamanho e localização dos defeitos. Como resultado, observou-se que quanto maior a temperatura de envelhecimento mais rápida foi a degradação das propriedades mecânicas e que as amostras que possuem silano, mantiveram maior resistência ao longo do tempo de envelhecimento. Também foi observado que o modo de falha de junta mudou com o passar do tempo e da temperatura tornando a falha adesiva a mais comum. Em relação ao ensaio de ultrassom, foi observado que a técnica de ultrassom foi eficiente para localizar e dimensionar o tamanho dos defeitos. Porém, não foi possível fazer uma comparação do aumento da área de defeitos com a variação das propriedades mecânicas. / [en] Composite materials have been developed to replace the use of metal alloys in high-performance applications, becoming widely used materials due to their broad combination of mechanical properties. Over the years, the pipeline sector has faced problems in pipelines due to aging and deterioration caused mainly by corrosion. To solve these problems, conventional repairs made with metallic materials are usually used to replace the damaged part. However, this process is very laborious, and the pipeline sector has seen the use of fiber-reinforced polymer composite materials as an alternative for repair. The main advantages compared to conventional repairs are high strength-to-weight ratio, low stress concentration, and easy application. However, many studies have shown that when exposed to aggressive environments such as temperature, humidity, and ultraviolet radiation, composite materials may deteriorate, meaning they lose their mechanical properties. Therefore, it is important to analyze the effect of these environments to predict the mechanical behavior, service life, and possible failures of adhesive joint repairs. In order to understand the mechanical behavior, adhesion, and service life of the adhesive joint, the aim of this work was to analyze the aging of repairs in a saline atmosphere. Double-Lap Shear (DLS) joints made of fiberglass-reinforced polymer composite on a steel substrate were used. The joints were made with four different surface treatments: I) Without Silane / manual sanding; II) Without Silane / Monti machine; III) With Silane / manual sanding; IV) With Silane / Monti machine. The bonded joint repairs were analyzed for the effects of temperature (35 degrees C, 55 degrees C, and 70 degrees C) and exposure to salt spray environments for an aging time of up to 6830h. The effect of aging and variation of mechanical properties were evaluated by destructive DLS testing, and non-destructive ultrasonic testing was used to detect the size and location of defects. As a result, it was observed that the higher the aging temperature, the faster the degradation of mechanical properties, and that samples with silane maintained greater resistance over the aging time. It was also observed that the joint failure mode changed over time and temperature, making adhesive failure more common. Regarding ultrasonic testing, it was observed that the technique was effective in locating and sizing defects. However, it was not possible to compare the increase in defect area with the change of the mechanical properties.