Abstract The reliability of reinforced concrete (RC) columns in a fire situation is investigated in this paper by combining the General, Equilibrium, and Isotherm at 500 ° C Methods. The well-known Monte Carlo (MC) and the First Order Reliability Method (FORM) are used in a parametric study for the column’s safety. The columns, in a biaxial bending-compression situations, are analyzed by an algorithm that takes into consideration physical and geometric nonlinearities. The dead and live load actions, steel and concrete material strengths, section geometry, model error, and temperature are among the random variables taken into consideration. The findings indicate that increasing the cover can dramatically reduce the probability of failure.

Resumo A confiabilidade de pilares de concreto armado (CA) em situação de incêndio é investigada neste artigo combinando os Métodos Geral, de Equilíbrio e da Isoterma a 500 ° C. O Método de Monte Carlo (MC) e o Método de Confiabilidade de Primeira Ordem (FORM) são usados em um estudo paramétrico sobre a segurança das colunas. Os pilares em situação de flexo-compressão oblíqua são analisados por um algoritmo que considera as não linearidades físicas e geométricas. As cargas permanentes e acidentais, resistências do material aço e concreto, geometria da seção, erro de modelo e temperatura estão entre as variáveis aleatórias levadas em consideração. Os resultados indicam que o aumento do cobrimento pode reduzir drasticamente a probabilidade de falha final.

Abstract This article aims to evaluate the reliability of cross-sections of simply supported reinforced concrete (RC) beams in a fire situation considering the utilization of the simplified method proposed in the Brazilian standard NBR 15200 [1]. The impact of the concrete cover, the live-to-total load ratio, and the quantity of heated beam faces were all taken into account in this analysis. Besides, a sensitivity analysis is performed showing the random variables that are of major impact on reliability. In the end, it was concluded that the number of heated faces of the beam is very important to the safety of these structures. Also, it is found that a higher concrete cover can promote an increase in reliability and that a bigger proportion of live load relative to the total load generates a decrease in the probability of failure. Regarding the sensitivity analysis, the fire temperature and the concrete cover were the variables with the greatest observed impact.

Resumo Este artigo tem como objetivo avaliar a confiabilidade de seções transversais de vigas de concreto armado (CA) simplesmente apoiadas em situação de incêndio, considerando a utilização do método simplificado proposto na norma brasileira NBR 15200 [1]. O impacto do cobrimento do concreto, a relação carga variável/carga total e a quantidade de faces aquecidas da viga foram levados em consideração nesta análise. Além disto, uma análise de sensibilidade é feita mostrando as variáveis aleatórias que apresentam maior impacto na confiabilidade. Ao final, concluiu-se que o número de faces aquecidas da viga é muito importante para a segurança dessas estruturas. Além disso, verifica-se que um maior cobrimento de concreto pode promover um aumento na confiabilidade e que uma maior proporção de carga variável em relação à carga total gera uma diminuição na probabilidade de falha. Em relação à análise de sensibilidade, a temperatura do incêndio e o cobrimento de concreto foram as variáveis de maior impacto observado.

resumo: Neste trabalho os autores têm por objetivo investigar uma metodologia para determinação dos pavimentos ótimos ao implementar outriggers (ORs) e belt-trusses (BTs) ao longo da altura de um edifício alto para reduzir tanto o máximo deslocamento lateral (MDL), quanto o momento na base do núcleo (MBN), de forma separada e concorrente. Além disso, analisa-se a influência destes elementos sobre outros critérios como a máxima aceleração e as frequências naturais. Ao longo do trabalho verifica-se o comportamento da estrutura quando a relação de rigidez dos principais elementos do sistema de contraventamento (núcleo, colunas perimetrais, OR e BT) são variados. Sendo assim, um modelo tridimensional de um edifício alto sob ação lateral de vento é analisado, empregando o método dos elementos finitos usando o software ANSYS. As otimizações mono e multiobjetivo foram resolvidas, respectivamente, pelo método Nelder-Mead modificado para variáveis inteiras pelos autores e pela função de utilidade. Diante dos resultados, conclui-se que ao introduzir de forma específica os ORs/ORs-BTs em edifícios altos a influência na redução dos objetivos mencionados é extremamente relevante, podendo chegar a 68% para o MBN e 71% para o MDL, dependendo de suas quantidades empregadas.

abstract: This paper aims to investigate a methodology for determining the optimum floor positioning of outriggers (ORs) and belt-trusses (BTs) over tall buildings height. The primary goal is to reduce the maximum lateral drift (MLD) and the core base moment (CBM), individually and concurrently. Furthermore, the influence of these elements on other criteria such as maximum acceleration and natural frequencies are analyzed. Throughout the work, the behavior of the structure is verified when the stiffness ratio of the main elements used in the bracing system (core, perimeter columns, OR, and BT) are varied. Therefore, a three-dimensional model of a tall building under lateral wind load is analyzed, using the finite element method with ANSYS software. The mono and multi-objective optimizations were solved, respectively, by the Nelder-Mead method with the author’s modifications to deal with integer variables and by a utility function. Based on the results, it is concluded that by specifically adding ORs/ORs-BTs in tall buildings the influence on the reduction of the mentioned objectives is extremely relevant, reaching up to 68% for the CBM and 71% for the MLD, depending on the amounts employed.

Abstract A metaheuristic approach for variable axial composites considering multiobjective optimization is investigated. The proposed methodology is based on the combination of three main parts: a methodology for defining the orientation of the fibers in the laminate, a structural analysis program (based on the Finite Element Method) and an optimization algorithm. It is important to highlight that a radial basis function (RBF), which describes a smooth fiber pattern, is generated using control points. The novelties of the present methodology consist of a proposal for a generalized parameterization technique, which allows the investigation of mechanical strength and stress concentration of variable axial composites. Thus, NSGA-II multiobjective genetic algorithm is used as optimization tool to define the fiber orientations. Besides, ax metaheuristic approach is used in situations when it is desirable to simultaneously minimize the stress concentration factor ( K t) and a failure criterion index ( F I or Φ). Two case studies are investigated: a double notched plate and a tube with a transverse hole.

Abstract This work presents an efficient approach to quantify uncertainties in composite laminates using the interval analysis, anti-optimization technique, and the α-cut procedure. The solutions are compared with the traditional and robust Monte Carlo method in 3 cases scenarios: natural frequencies, buckling, and strength safe factor. For natural frequencies and buckling loads, the presented Interval based methodology showed 2.5% to 4.5% larger error values when compared to the Monte Carlo method using the same number of function calls. This implies a larger uncertain area, and hence, a better solution. For the strength test using Tsai-Wu failure theory, the error values are even greater: 22% to 46%. A violation of the failure limit was detected by the proposed Interval based approach, but not detected by Monte Carlo method. The solutions show that the presented methodology yields a safer and more precise analysis when compared to the traditional Monte Carlo approach.

INTRODUCTION: The cycling activity has increased in recent years, either as a means of leisure or physical activity or as means of transport. Discomfort is one of the main complaints for cyclists, especially when related to the type o pavement they use while riding. This work presents a study of measurement and evaluation of human exposure to hand-arm vibration in the leisure cyclist activity in different pavements in order to classify according to vibration discomfort and to vibration injury risk. METHODS: Vibration measurements are performed for three pavement types, asphalt (AS), precast concrete slab (PC), and interlocking concrete blocks (BI), using two bicycle models (time trial speed racing bike, S and mountain bike, MB), and cyclists with different physical characteristics. It is performed a quantitative analysis of each configuration - pavement type × bike model × cyclist - where the daily vibration exposure A(8) is evaluated, as defined in ISO 5349-1 Standard, for 2h daily exposure. It is also evaluated the maximum daily exposure in order to reach limit values, as defined by Directive 2002/44/EC. RESULTS: Based on a subjective analysis (survey), it is evaluated the comfort degree for vibration exposure for each tested pavement, according to a survey within cyclists. Finally, the results are compared using both quantitative and subjective analysis. CONCLUSIONS: Not surprisingly, it has been noticed that the most comfortable pavement type is the asphalt pavement (AS), followed by the precast concrete pavement (PC) and by the interlocking concrete blocks pavement (BI), confirming the opinion pool within cyclists. As a new finding, for some pavement types, bikes and daily journey activities, the vibration levels may reach health limit levels which justify the originality of the work and the importance as guidance for healthy public decisions for new cycle paths.

INTRODUCTION: The human body may interact with the structures and these interactions are developed through the application of contact forces, for instance due to walking movement. A structure may undergo changes in the dynamic behaviour when subjected to loads and human bodies. The aim of this paper is to propose a methodology using Artificial Neural Networks (ANN) to calibrate a force platform in order to reduce uncertainties in the vertical Ground Reaction Force measurements and positioning of the applied force for the human gait. METHODS: Force platforms have been used to evaluate the pattern of applied human forces and to fit models for the interaction between pedestrians and structures. The designed force platform consists in two force plates placed side by side in the direction of walking. The reference voltages applied to the Wheatstone bridge were used for calibration as the input data to the ANN, while the output data were the estimated values of the standard weights applied to the force platform. RESULTS: It was presented a framework to enhance traditional calibration methods for force platforms (vertical component) using an ANN. The use of ANN shows significant improvements for the measured variables, leading to better results with lower uncertain values that are smaller than those using a simple traditional calibration. CONCLUSION: The results suggest that the calibration with the ANN method may be useful in obtaining more accurate vertical Ground Reaction Forces and positioning measurements in a force platform for human gait analysis.

This paper provides some information and numerical tests that aims to investigate the use of a Fuzzy Controller applied to control systems. Some advantages are reported regarding the use of this controller, such as the characteristic ease of implementation due to its semantic feature in the statement of the control rules. On the other hand, it is also hypothesized that these systems have a lower performance loss when the system to be controlled is nonlinear or has time varying parameters. Numerical tests are performed using modal LQR optimal control and Fuzzy control of non-collocated systems with full state feedback in a two-dimensional structure. The paper proposes a way of designing a controller that may be a supervisory Fuzzy controller for a traditional controller or even a fuzzy controller independent from the traditional control, consisting on individual mode controllers. Some comments are drawn regarding the performance of these proposals in a number of arrangements.