Papers by Carlos Alberto Caridade Monteiro Couto
ce/papers, Sep 1, 2022
Steel portal frames are common structures used in practice. Owing to their optimization, members ... more Steel portal frames are common structures used in practice. Owing to their optimization, members with tapered geometry and slender sections are prevalent. Since local buckling is a possible mode of failure, an additional complexity arises that requires the use of shell finite elements to assess the ultimate capacity of these structures. On the other hand, imperfections, either of geometric or material nature, must be considered because they are unavoidable and reduce the overall capacity of the frames to carry load. The main focus of this study is therefore to characterize the influence of imperfections. Plate imperfections (or local), global (or member) and frame imperfections, are considered as well as material imperfections such as residual stresses that may contribute to degrade the frame's behaviour.An extensive parametric study comprising a total of 24 frames and 15 different imperfection sets was carried out and based on this large pool of results, recommendations for the definition of imperfections are given and conclusions are drawn on their influence. This work aims to be a step further in establishing a numerical framework to generate results that can be later used to validate existing design methods.
Structural Engineering International, May 25, 2022
This paper describes a method for analyzing and predicting the timing properties of a program fra... more This paper describes a method for analyzing and predicting the timing properties of a program fragment. The paper first presents a little language implemented to describe a processor's architecture and a static WCET estimation method is then presented. The timing analysis starts by compiling a processor's architecture program followed by the disassembling of the program fragment. The assembler program is then decomposed into basic blocks and a call graph is generated. These data are later used to evaluate the pipeline hazards and cache miss that penalize the real-time performance. Finally, some experimental results of using the developed tool to predict the WCET of code segments with some Intel microcontroller are presented.
ce/papers, Sep 1, 2019
The General Method (GM) covers the safety check of structural elements with complex support condi... more The General Method (GM) covers the safety check of structural elements with complex support conditions and/or of non-prismatic members. However, it's not widely validated at normal temperature and is inexistent in fire part of the Standard EN 1993-1-2. With that in mind, this investigation aims at proposing and validating the GM to perform the safety check of unrestrained tapered columns at elevated temperatures. This is done, first, by including, in the original formulation, the reduction of steel material properties with the temperature, and later by improving the EN 1993-1-2 out-of-plane buckling curve. With this novel approach, the GM shows good agreement to numerical results and produces accurate predictions of out-of-plane resistance for tapered columns at elevated temperatures.
This paper presents a comparison between three switching techniques that can be used in three-pha... more This paper presents a comparison between three switching techniques that can be used in three-phase four-wire Shunt Active Power Filters (SAPFs). The implemented switching techniques are: Periodic-Sampling (PS), Triangular Carrier Pulse-Width Modulation (TC-PWM) and Space Vector PWM (SVPWM). The comparison between them is made in terms of the compensated currents THD%, implementation complexity, necessary CPU time and SAPF efficiency. To perform this comparison are presented and analyzed several experimental results, obtained with a 20 kVA Shunt Active Power Filter prototype, specially developed for this purpose. The control system of the developed SAPF is based in the p-q Theory with a grid synchronization algorithm p-PLL.
Applications of Structural Fire Engineering, Jan 18, 2016
According to the Eurocode 3 Part 1-2 (EN1993-1-2) (CEN 2005b), it is possible for structural engi... more According to the Eurocode 3 Part 1-2 (EN1993-1-2) (CEN 2005b), it is possible for structural engineers to consider physical based thermal actions and to do performance based design instead of using prescriptive rules based on nominal fire curves. However, some uncertainties remain in the use of such approaches. This study focus on the clarification of the use of the simplified design methods to assess the fire resistance of unbraced steel frames exposed to fire. On the other hand, a recent study (Couto et al. 2013) suggests the use of a buckling coefficient of 1.0 for all the columns except those belonging to the first storey of a pinned framed where 2.0 should be taken instead and it is unclear if the consideration of such values for the buckling lengths is adequate when using performance based designs. In this study, a comparison is made between simple and advanced calculation models and it is demonstrated that the simple design methods, using the suggested buckling coefficients to calculate the fire resistance of the frames are safe sided when compared to the use of advanced calculations using the finite element method (FEM).
Thin-walled Structures, May 1, 2022
DOAJ (DOAJ: Directory of Open Access Journals), 2000
This paper describes the study of the research program being carried out on the feeding system of... more This paper describes the study of the research program being carried out on the feeding system of an industrial overlock sewing machine. The results obtained from the presser foot bar displacement and compression force, together with the graphic kinematic analysis, which includes the velocity and acceleration taken from the displacement-time curves of the presser bar, led to further understanding of the feeding system dynamics. This study is providing the basis for the development of a redesigned and optimized fabric feeding system. The new actuation system, based on a proportional force solenoid integrated in the presser foot bar, will be also discussed as an important contribution to achieving a desired dynamic behaviour at high sewing speeds.
A typical sensing module is composed of sensors, interface electronics, a radio-frequency (RF) CM... more A typical sensing module is composed of sensors, interface electronics, a radio-frequency (RF) CMOS transceiver and an associated antenna. A 2.4-GHz RF transceiver chip was fabricated in a UMC 0.18 μm CMOS process. The receiver has a sensibility of-60 dBm and consumes 6.3 mW from a 1.8 V supply. The transmitter delivers an output power of 0 dBm with a power consumption of 11.2 mW. Innovative topics concerning efficient power management was taken into account during the design of the transceiver. A solution of individual sensing modules allows a plug-and-play solution. The target application is the integration of a wireless sensor network in smart electronic shirts, for monitoring the cardio-respiratory function and posture. I.
Structures, Dec 1, 2021
Abstract The accuracy of different fire design methodologies for hollow cross-sections subject to... more Abstract The accuracy of different fire design methodologies for hollow cross-sections subject to compression and major-axis bending is studied and compared in this paper. For that purpose, a numerical model based on shell finite elements is developed and validated against existing experimental results available in the literature. Comprehensive numerical parametric studies are then carried out by means of the validated numerical model, including different cross-section dimensions, loading conditions, steel grades and temperatures, to obtain a large set of results of the ultimate resistance of hollow sections in fire. Based on these results, the existing design rules of the Eurocode 3 Part 1–2, the AISC 360 specification and the recent design proposals of Couto et al. [1,2] and the Direct Strength Method adapted to fire are assessed in terms of their accuracy for predicting the section capacity, including the resistance against local buckling at elevated temperatures. It is demonstrated that the cross-sectional classification procedure for the case of fire, available in the Eurocode 3 and AISC specifications, results in inconsistencies and should be further investigated and revised in the future. To overcome the Eurocode 3 limitations it is proposed that the design methodology of Couto et al. [1,2] is adopted irrespective of the cross-section classification and for the AISC specification it is suggested the use of a reduced stress based on the 0.2% proof strength until more efficient design methods are developed.
Springer eBooks, 2001
This paper reports the design, modelling, fabrication and assembly of a silicon bulk-micromachine... more This paper reports the design, modelling, fabrication and assembly of a silicon bulk-micromachined soil moisture microsensor using the Dual-Probe Heat-Pulse (DPHP) method. Soil humidity measurement is essential to study soil preservation and control the development of plants, namely in closed ecosystem. The DPHP method uses a heater (Peltier effect) and a temperature probe (Seebeck effect) to determine the volumetric heat capacity of the soil and hence water content (θ v). This is the first time that the DPHP method is implemented in a microdevice and the first integrated sensor for soil moisture. This microdevice is more suited to measure at different soil depths in a non-destructive and automated manner.
Structures, May 1, 2017
The fire design of a steel frame is defined according to Part 1.2 of Eurocode 3 (EN 1993-1-2). It... more The fire design of a steel frame is defined according to Part 1.2 of Eurocode 3 (EN 1993-1-2). It is based on security check to standard ISO 834 fire, where the structure must resist to fire during time set by regulation. For a natural fire, the structural resistance is ensured in the way that the collapse does not occur during the fire, including fire decline phase, or alternatively for a certain period. The Eurocode makes it clear that to check the standard fire resistance requirements it is enough to perform analysis of elements but does not report if such analysis is sufficient for a natural fire design and some uncertainties remain. This study focus on the clarification of the use of the simplified design methods for assessment of the fire resistance of steel frames exposed to natural fire scenarios. Special attention is drawn to the use of the buckling lengths suggested in EN 1993-1-2 for the fire design of columns in braced frames and a recent proposal for unbraced frames suggesting the use of a buckling length of 1.0L for all columns except those belonging to the first storey of pinned frames where 2.0L should be taken instead. Finally, a comparison is made between simple and advanced calculation models and it is demonstrated that the simple design methods, using the suggested buckling lengths to calculate the fire resistance of the frames are safe sided when compared to the use of more advanced calculations by means of the finite element method (FEM).
Proceedings of SPIE, Jul 1, 2005
This paper presents a wireless sensor network for smart electronic shirts. This allows the monito... more This paper presents a wireless sensor network for smart electronic shirts. This allows the monitoring of individual biomedical data, such the cardio-respiratory function. The solution chosen to transmit the body's measured signals for further processing was the use of a wireless link, working at the 2.4 GHz ISM band. A radio-frequency transceiver chip was designed in a UMC RF 0.18 µm CMOS process. The power supply of the transceiver is 1.8 V. Simulations show a power consumption of 12.9 mW. Innovative topics concerning efficient power management was taken into account during the design of the transceiver.
Soil Dynamics and Earthquake Engineering, 2020
Large earthquakes may cause a chain of events, and one of which can be fire after an earthquake. ... more Large earthquakes may cause a chain of events, and one of which can be fire after an earthquake. The effects of fire after earthquake on urban areas can be even worse than the effects of the earthquake itself. Buildings are not adequately designed for fire after an earthquake since most standards ignore that possibility. The aim of the work is to evaluate the consequences of the damage introduced due to the seismic events on the fire resistance of reinforced concrete elements. Several numerical analyses were performed to reinforce concrete elements using the program SAFIR, considering the thermal and mechanical analysis of the structure. The main variables in the analysis were the type of damage in the elements and the type of loads. The thermal analysis was performed using the standard fire curve ISO 834. The results show that the damage imposed by earthquake on reinforced concrete structures reduces the fire resistance, especially if the cover of the elements is removed and the reinforcement is exposed to fire.
Journal of Constructional Steel Research, Jun 1, 2016
Abstract This paper describes an investigation on the critical temperatures of slender cross-sect... more Abstract This paper describes an investigation on the critical temperatures of slender cross-sections according to Eurocode 3 design. Slender cross-sections are prone to local buckling, which, as the name implies, is characterized by a local failure that occurs in the presence of compressive stresses and prevents the cross-sections from developing their full plastic bending resistance or axial compression resistance, which leads to the reduction of the load bearing capacity. Eurocode 3 classifies these cross-sections as Class 4, the highest class, and suggests a default critical temperature of 350 °C irrespective of the load level conditions. This study demonstrates that this temperature is too conservative especially if different degrees of utilization of the cross-section are taken into account. The establishment of a default critical temperature is invaluable from a practical standpoint and, therefore, it is the purpose of this work to recommend and validate new default critical temperatures for Class 4 cross-sections subject to compression and bending about the major axis for different reduction factors for the design load level under fire conditions, based on an extensive numerical investigation. From this study, it is observed that the critical temperatures for such cross-sections are within the range of 400 °C and 600 °C for the usual load levels and, based on that, new default critical temperatures are suggested.
Thin-walled Structures, Feb 1, 2019
In this work, an appraisal of the influence of the residual stresses and geometric imperfections ... more In this work, an appraisal of the influence of the residual stresses and geometric imperfections is carried out for thin-walled I-shaped sections covering both hot-rolled and welded profiles based on a numerical study using the Finite Element Method. The Eurocode 3 design provisions for local buckling are presented and evaluated in comparison to the numerical results. Several residual stress patterns and geometric imperfection's amplitude and shape are considered to determine their effect on the ultimate strength of the cross-sections. Additionally, it is described a procedure to assess the flange and web interaction under different imperfection assumptions, and its influence investigated. The conclusions from this study are that the Eurocode 3 design provisions for hot-rolled sections are appropriate, but should be further improved for welded sections, mainly because the influence of the welded residual stresses is detrimental for the cross-section capacity and its effect is not to accounted for adequately. Finally, this study provides relevant information for the numerical modelling of thin-walled I-shaped sections concerning the consideration of geometrical imperfections and residual stresses. Regardless of the efforts of Winter in providing a lower bound resistance curve, that included the experimental results, like the one preconized by Eq. (1), due to the lack of information about the imperfections and residual stresses of the tested specimens, it is difficult to
Revista da Estrutura de Aço, 2016
Resumo Os projetos estruturais dividem-se em duas partes distintas: a análise do comportamento gl... more Resumo Os projetos estruturais dividem-se em duas partes distintas: a análise do comportamento global, ou seja, a determinação dos esforços e dos deslocamentos; a verificação dos elementos e dimensionamento das ligações, devendo-se considerar na análise os efeitos não lineares geométricos globais e locais, o comportamento elastoplástico do material e as imperfeições globais e locais. Nesse artigo são abordados os principais aspetos relacionados com a análise e estabilidade estrutural de pórticos metálicos da EN 1993-1-1:2010 e da ABNT NBR 8800:2008 partir da comparação da análise estrutural de três pórticos planos utilizando metodologias simplificadas e análises numéricas recomendadas pelas duas normas técnicas. Verificou-se que os efeitos de 2ª ordem afetam significativamente os esforços internos e deslocamentos da estrutura, observaram-se resultados satisfatórios com os métodos aproximados e proximidade entre os resultados obtidos com a norma brasileira e aqueles obtidos com a norma europeia. Palavras-chave: Estruturas de aço; Efeitos da deslocabilidade global; Método da amplificação dos esforços solicitantes; Análise numérica.
The fabrication (using planar thin-film technology) of Bi 2 Te 3 and Sb 2 Te 3 microstructures, w... more The fabrication (using planar thin-film technology) of Bi 2 Te 3 and Sb 2 Te 3 microstructures, with high thermoelectric figure of merit, suitable for incorporation in Peltier elements and thermopiles, is reported. The microstructures were fabricated by co-evaporation of Bi and Te, for the n-type element, and Sb and Te, for the ptype element, on a 25 µm-thick polyimide (kapton) substrate. Kapton film is a flexible, robust substrate with a low thermal conductivity. While the plastic mechanical properties allow conformal coverage of surfaces with many different shapes without apparent damage of film or substrate, Kapton low conductivity ensures that the devices will not be thermally shorted through the substrate. High figures of merit are reported, sufficient to achieve more than 10ºC of cooling over a 1 mm 2 area.
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Papers by Carlos Alberto Caridade Monteiro Couto