Prototyping Elliptically Profiled Inverted Pendulum Walls in Cross-laminated Timber (CLT) for Passive Self-centering and Seismic Resiliency

Cross-laminated timber (CLT) buildings garnered international attention, nearly a decade ago, for elevating wood construction to new heights on fully panelized assemblies of floors and walls. While highly regarded as a sustainable building material, use of CLT as a structural wall system depends on seismically resilient strategies like controlled rocking. This project prototyped elliptically profiled CLT panels and slotted-pin steel connections, at full-scale, to produce rolling and slip-friction inverted pendulum wall systems of one-story height and inspired by seismic isolation concepts. Digital fabrication realized elliptical profiles along the load-bearing edges of six 5-ply CLT panels and various customized slot shapes for accompanying steel connections. Pins traveling within V-shaped slots intended only to guide rolling as displacement restraints, in contrast with pins constrained within vertical slots that forced panels into slip-friction combinations of rolling and sliding. Six CLT panels and two versions of shear transfer connections yielded a total of 12 full-scale wall prototype configurations for cyclic lateral load-displacement testing that emulated standard quasi-static protocols for seismic isolation. The hysteresis plots generated by the tests confirmed that elliptical eccentricity predictably controlled effective lateral stiffness and displacement capacity, while providing inherent self-centering. When configured to roll using traction along steel bearing surfaces as the primary mechanism of story shear transfer, CLT panels supported simulated gravity loads as high as 400 kN (90 kips) while achieving story drifts commonly exceeding 10 and even 20 percent. When configured to transfer shear primarily through a pin connection, however, CLT panels slid and sustained damage that limited gravity load capacity to 133 kN (30 kips). Connection constraint, therefore, dictated whether friction essentially transferred story shears transfer or dissipated energy. To help explain implications of friction, Digital Image Correlation (DIC), piezoelectric film pressure mapping, Finite Element Analysis, and fundamental free-body diagrams visualized the behavior of high-pressure contact between timber and steel. Despite the low damping exhibited by rolling and increased damage of slip-friction rocking, both models of elliptically profiled rocking walls can develop into viable options for isolation planes within multistory building schemes, based on the results of this study

What the avian eye tells its brain: processing of chromatic and achromatic information at the level of chicken retinal ganglion cells

Birds have highly sophisticated vision, including tetrachromacy but it is unknown how visual information is processed within the retina. Using a high density multielectrode, stimulus driven extracellular electrical signals of multiple retinal ganglion cells (RGC) were measured in parallel. Twenty-seven functionally distinct RGC types were identified by clustering, revealing major principles of avian RGC electrophysiology: Firstly, most RGCs were excited by both ON and OFF steps, and had complex chromatic sensitivities and opponency responses, often in combination with wavelength dependent and long response latencies in the ON channel. These RGCs resemble small bistratified (blue-ON) RGCs in the primate retina. A second group of RGCs showed OFF dominant responses, faster response latencies, and simpler spectral sensitivities, likely matching double cones. These cells potentially form a classical achromatic contrast pathway, like primate alpha/parasol RGCs. Focusing on wavelength dependent response latencies, we found that except for near UV responses, long wavelength ON-responses yielded the shortest latency and most synchronised responses, consistently followed by shorter wavelengths. Combining these insights, we used principal component analysis of flash-responses to reveal that greyscale and “colour” stimuli are encoded in a near-orthogonal manner. We tentatively suggest that birds use a combination of time- and opponency-coding to represent spectral information, while a smaller proportion of cells act as fast greyscale OFF channels which serve achromatic vision

Development of hybrid composite plate (HCP) for strengthening and repair of RC structures

Tese de Doutoramento em Engenharia CivilThis research work deals with development of a novel retrofitting element for RC structures designated as “Hybrid Composite Plate (HCP)”. This prefabricated element is composed of a thin strain hardening cementitious composite (SHCC) plate reinforced with either near surface mounted CFRP (NSM-CFRP) laminates, designated as HCP(L), or externally bonded CFRP (EB-CFRP) sheets, designated as HCP(S). From the materialstructural point of view, this system benefits from the high ductility of SHCC and the high tensile strength of CFRP in retrofitting of RC structures. HCP is essentially tailored to be significantly free of the shortcomings identified in the most advanced available retrofitting techniques, such as textile reinforced mortar (TRM) and conventional FRP systems. Furthermore, it is possible to attach this proposed system to the RC members by means of either adhesive, chemical anchors or a combination thereof. The investigation carried out is mainly dedicated to the development of HCP and assessment of its structural efficiency for upgrading/repairing RC members with a variety of retrofitting demands. In this framework, series of experimental tests are executed to assess HCP retrofitting efficiency for upgrading shear, flexural and energy dissipation capacity of RC members. Results of these experimental tests confirmed HCP’s high potential for retrofitting RC structures. An analytical approach is presented to estimate the ultimate flexural capacity of the beams with an HCP attached to their soffit, which is further complemented with a numerical strategy to predict the load-deflection response of such retrofitted beams. The proposed analytical and numerical approaches accurately predict the flexural capacity and load-deflection response, of flexurally strengthened beams using HCP. Finally, adopting a combination of experimental tests and finite element modelling, recommendations for an optimized HCP(L) and its connection with concrete are provided. The local bond stress-slip models at the interface of CFRP-SHCC and interface of HCP(L)- concrete are determined. Based on results obtained, equations correlating the pull force capacity of the HCP(L) to the CFRP-SHCC bond length for CFRP laminates with two different axial stiffness are derived.Esta tese apresenta a investigação realizada para o desenvolvimento de um novo elemento visando o reforço de estruturas de betão armado (BA) designado por Hybrid Composite Plate (HCP). Este elemento consiste num painel pré-fabricado composto por uma fina camada de material de matriz cimentícia apresentando comportamento de endurecimento em tração ( SHCC) reforçada laminados de matriz polimérica reforçada com fibras de carbono (CFRP) inseridos à superfície (Near Surface Mounted), designado por HCP(L), ou com manta de CFRP aplicada segundo a técnica de colagem exterior (externally bonded, EB-CFRP), designadas por HCP(S). Do ponto de vista estrutural, este sistema beneficia da alta ductilidade do SHCC e da elevada resistência à tração do CFRP no reforço de estruturas de BA. O HCP afigura-se como uma solução apropriada essencialmente por não apresentar as deficiências identificadas nas técnicas mais avançadas de reforço estrutural atualmente disponíveis, tais como TRM (Textile Reinforced Mortar) e sistemas FRP (Fiber Reinforced Polymer). O sistema proposto permite uma ligação aos elementos de BA através de resina epóxi, ancoragem química ou uma combinação entre estes. A investigação realizada foi dedicada ao desenvolvimento do HCP e avaliação da sua eficiência estrutural para melhorar ou reparar elementos de BA para uma variedade de exigências de reforço. Com este objetivo, uma série de ensaios foram realizados para avaliar a eficiência do reforço do HCP ao corte, flexão e capacidade de dissipação de energia de elementos de BA. Uma formulação analítica foi desenvolvida para estimar a resistência à flexão de vigas de BA reforçadas com HCP ligado à sua face inferior. Esta abordagem foi completada com um modelo numérico para prever a resposta carga-deformação destas vigas. A formulação analítica e o modelo numérica propostos previram com precisão, respetivamente, a capacidade de flexão e a resposta carga-deformação de vigas reforçadas com HCP. Finalmente, com base na combinação de resultados de ensaios experimentais e modelos de elementos finitos, são fornecidas recomendações para a otimização do HCP(L) e a sua ligação ao betão. Para a caracterização das interfaces CFRP-SHCC betão-HCP(L) foram determinadas leis tensão versus deslizamento. Com base nos resultados obtidos, apresentamse as equações que relacionam a capacidade de carga à tração do HCP(L) com o comprimento de ligação do CFRP-SHCC composto por camadas de CFRP dotadas de rigidez distinta.Fundação para a Ciência e a Tecnologia (FCT) SFRH/BD/65663/2009.Fundação para a Ciência e a Tecnologia (FCT) PTDC/ECM/114511/200

Design considerations for a miniature atmospheric engine with a magnet-actuated autonomously-reciprocating in-cylinder regenerator for portable power production

Driven by the need for high energy-density power sources, demand has stimulated the development of small-scale engines. A small-scale engine with a fuel supply could replace batteries and utilize higher energy-density liquid hydrocarbon fuels; such an advance could deliver a new age of portable devices. Currently, operable small-scale engines exist; yet their efficiencies are poor. One possible alternative for improving efficiency is the incorporation of thermal regeneration. This thesis develops a concept for an efficient miniature reciprocating engine for portable power production that is based upon the regenerated atmospheric cycle and uses a magnet-actuated in-cylinder regenerator. As part of the development of the proposed engine, a dynamic model of the regenerator was developed concurrently with an engine simulator. The dynamic model was validated using the engine simulator and can now be used to develop a model to study the thermal aspects of regeneration. The engine simulator was also used to study a unique lubrication-free low-friction piston-cylinder set that utilizes a graphite-glass clearance seal. The piston cylinder set was subjected to several pressure tests, including one with a 26 h duration. It was found that with the addition of aspiration slots, the piston cylinder set with the engine simulator operating at 1800 rpm could reach a peak pressure of approximately 370 kPa with a pressure ratio of approximately 4.2. For the 26 h long-duration test, it was found that the graphite piston did not show any significant wear. However, elastomer cups that were part the ball-joint supports for the piston did exhibit wear that lead to a decrease in peak cycle pressure with time

Fracture mechanics life analytical methods verification testing

The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable

Synthesis of sulphonated and transition metal oxide doped polymeric nanocomposites for application in design of supercapacitors

Philosophiae Doctor - PhDTo meet a fast-growing market demand for next generation portable electronic devices with higher performance and increased device functionalities, efficient electrical energy devices with substantially higher energy, power densities and faster recharge times such as supercapacitors are needed. The overall aim of this thesis was to synthesize nanostructured sulphonated polyaniline and transition metal single, binary and ternary mixed oxide doped nanocomposites with electro-conductive properties. These nanocomposites were anchored on activated graphitic carbon and used in design of asymmetric supercapacitors. Tantalum(IV)oxide, tantalum(IV)oxide-nickel(II)oxide, tantalum(II)oxide-manganese(III)oxide, tantalum(II)oxide-nickel(II)oxide-manganese(II,III)oxide nanoparticles were synthesised using modified sol-gel methods. These were then dispersed, individually, in acidic media through sonication and incorporated in-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped with poly(4-styrene sulphonic acid). These novel polymeric nanocomposites were characterised with FTIR, UV-visible, TEM, SEM, EDS, XRD to ascertain successful polymerization, doping, morphology and entrapment of the metal oxide nanoparticles. SECM approach curves and interrogation of CV revealed that these nanocomposites are conductive and electro-active. The cells showed good supercapacitor characteristics with high specific capacitances of 170.5 Fg⁻¹ in TaO₂- PANi-PSSA, 166.1 Fg⁻¹ in TaO₂-NiO-PANi-PSSA, 248.4 Fg-1 in TaO-Mn₂O₃-PANi- PSSA and 119.6 Fg⁻¹ in TaO-NiO-Mn₃O₄-PANi-PSSA. Their corresponding energy densities were calculated as 245.5 Whg⁻¹, 179.4 Whg⁻¹, 357.7 Whg⁻¹ and 172.3 Whg⁻¹ respectively. They also gave respective power densities of 0.50 Whg⁻¹, 0.61 Whg⁻¹, 0.57 Whg⁻¹ and 0.65 Whg⁻¹ and showed good coulombic efficiencies ranging between 77.97% and 83.19%. These materials are found to have a long cycle life and therefore good electrode materials for constructing supercapacitor cells.National Research Foundation (NRF

Effect of Intraocular Pressure on Chick Eye Geometry, Finite Element Modeling, and Myopia

In most cases, myopia is characterized by an increase in axial length of the eye, but the exact mechanisms for the axial elongation are still unknown. Higher intraocular pressure (IOP) has been associated with myopia and could be involved in eye enlargement. Also, some investigators have argued that the mechanical stresses generated by the ocular muscles during near work cause the eye to stretch out of shape. The purpose of this work was to investigate the effect of IOP on eye geometry, build a finite element model of the corneo-scleral shell of a chick eye, and verify if the eye could elongate due to increased IOP and hence become myopic. In the present study, myopia was induced in the right eye of chicks using -15 dioptre (D) goggles. The in-vitro pressure-volume curves of normal and myopic chick eyes were obtained using a computer controlled syringe pump and a digital pressure gauge. The axial length and horizontal equatorial diameter of the chick eyes as pressure increased were measured from digital photographs. To build the finite element model, normal chick eyes were frozen, sliced using a microtome, and photographed. The image sequence was aligned using MATLAB software and imported into SolidWorks® and Mimics software packages for three-dimensional (3D) reconstruction. Three 3D models were constructed and imported into Abaqus/CAE® software for finite element analysis. Isotropic, homogeneous, linear elastic and exponentially stiffening material properties were used for the finite element models. The results of the finite element models were compared with the experimental data. The results showed that normal chick eyes elongated in the axial direction and initially contracted in the horizontal equatorial direction as IOP increased. Myopic chick eyes did not elongate as much in the axial direction and did not contract as much in the horizontal equatorial direction compared with normal eyes. The volumetric deformation of myopic eyes was similar to normal eyes suggesting that growth and remodelling of the ocular tissues was involved in experimental myopia in the chick. The 3D reconstructed geometry of a chick eye was similar to a real eye although small geometric inaccuracies were present. The finite element model with isotropic, homogeneous, and exponentially stiffening material properties agreed well with the experimental strains in spite of the fact that the anisotropy of the ocular tissues was not included in the finite element model. This suggests that the oblate geometry of the chick eye was the main parameter dictating its deformation under increased IOP. The natural tendency of chick eyes is to elongate in the axial direction as IOP increases and this suggests that IOP could play a role in myopia onset and progression. The way chick eyes deformed as pressure increased is probably due to their oblate geometry. The finite element model could be used in the future to study the effect of different parameters such as ocular muscle forces and ocular tissues material properties on eye geometry. This way, an eye configuration more prone to eye elongation and myopia could be determined