Resumo O Brasil carece de uma legislação sobre alvenaria estrutural em situação de incêndio. Por conta disso, o Corpo de Bombeiros do Estado de São Paulo (2011) recomenda que se faça esse dimensionamento de acordo com as recomendações do Eurocode 6 (2005) ou norma internacional similar. Com o intuito de subsidiar futuras discussões sobre uma normatização nacional, neste artigo são apresentados os procedimentos de dimensionamento da alvenaria estrutural em situação de incêndio em vigor nos Estados Unidos, na Europa e na Austrália. Ao final, sem deixar ao largo o questionamento da aplicabilidade dessas três normas à situação brasileira, por conta das diferenças de materiais utilizados tanto nos blocos quanto nos acabamentos, sugere-se mesclar o que há de interessante nesses três códigos internacionais, de forma gradativa, na elaboração de futura norma brasileira sobre o assunto.
Utilização de fíler cerâmico e sílica ativa na composição de argamassa com baixo teor de cimento The use of ceramic filler and active silica with low cement content mortar
Neste trabalho, foi analisada a viabilidade de emprego de cola à base de PVA e argamassa de solo-cimento no assentamento de paredes de alvenaria de tijolos maciços de solo-cimento, em substituição à argamassa usual (cimento, cal e areia). Pequenos prismas, executados com quatro tijolos maciços de solo-cimento e assentados com as argamassas e a cola de PVA, foram ensaiados à compressão e à flexão. Os resultados dos ensaios dos prismas executados com a argamassa de assentamento usual foram tomados como padrão esperado de comportamento para os outros prismas executados com argamassa de solo-cimento e com cola de PVA. Os resultados obtidos nos ensaios dos prismas indicaram que tanto cola à base de PVA quanto argamassa de solo-cimento podem ser empregadas, satisfatoriamente, no assentamento de painéis de alvenaria de tijolos maciços de solo-cimento.
For the dimensioning of structural elements in fire situation, simplified equations and parameters are commonly used in analytical equations or numerical models. More complex equations or simplified values can be chosen by the designer for determine materials properties in high temperature in numerical models, however, numerical modeling can be quite sensitive to the variation of some of the physical and mechanical properties. In this paper, the sensitivity of the numerical model in relation to the values according to the level of simplification chosen was evaluated, presenting an analysis in relation to the results found to contribute to the choice of these parameters and presenting the indications found in the literature. In this sense, this work presents a study of sensitivity to the variation of the values of steel and concrete properties, presented in the Eurocode and Brazilian standards, in addition to the moisture content and emissivity of the surface exposed to fire, for the dimensioning, in a fire situation, of steel tube columns, of circular and square section, filled with concrete. The studies were carried out via numerical modeling developed in the software ABAQUS. It was verified that the resulting emissivity values equal to 0.7 or 0.8, recommended in the literature, are conservative, and the choice of either does not bring significant changes in the temperature field obtained for the structural elements under analysis. It was also verified that the concrete moisture content is a relevant aspect for the formation of its temperature field, also affecting, but to a lesser extent, the steel temperature. Regarding the physical and mechanical properties of the materials, this sensitivity study suggests the adoption of the values from the equations presented in Eurocodes, without simplifications, and with the specific heat and thermal conductivity of the concrete, adopted in accordance with the Eurocode 4.
The composite structures formed by the association of steel profiles with concrete have shown to be an advantageous alternative, improving the behavior of the steel structures concerning their load capacity, stiffness, and durability, under fire conditions. The concrete-filled tubular columns have become an attractive alternative for the civil construction area, offering constructive and esthetic advantages. The Eurocode 4 (EN 1994(EN -1-2, 2002 and ABNT NBR 14323:2013 show simple methods for the design of the composite columns under fire situations. Nevertheless, these present limitations in their application. In addition, regarding the determination of the temperature field in the cross section, the Eurocode 4 (EN 1994-1-2, 2002) describes a specific procedure for columns with section profile covered with concrete, but it is neglectful about concrete-filled tubular columns. The goal of this paper is to present a simplified procedure to determine the temperature registered in concrete-filled steel columns and apply the procedure to columns with square section tubes. The temperature distribution was determined by simulations using the computer package ABAQUS (Dessault Systemes Simulia Corp. 2013). After the studies, it has been considered that the procedure described in this paper is an effective alternative for the determination of the field's temperature and for the application of the design of the concrete-filled columns under fire conditions.
The reduction of natural resources combined with a substantial increase in the generation of solid waste in large urban centers, justifies the search for methods of reusing the construction industry waste. The ceramic industry has a high disposal rate during the manufacturing, transportation and eventual replacement of its products. In this case, research on the reuse of ceramic materials is urgent. A possible solution is the employment of ceramic waste as a coarse aggregate in structural concrete. Therefore, the mechanical properties of this new mix of concrete have to be assessed. This study evaluates the bond strength between steel rebar and concrete with ceramic waste aggregates, by means of the pull-out test method, proposed by RILEM-FIP-CEB (1978). Three concrete mixtures were produced: a mixture without any replacement, and two other mixtures with gradual substitution of natural coarse aggregate by ceramic coarse aggregate (40% and 100% substitution, in volume). Nine cylindrical specimens, three for each of the concrete mixtures, were evaluated in laboratorial conditions. Results concerning bond stress between concrete and steel rebar indicated the feasibility of employing ceramic waste to replace part of the coarse aggregate in structural concrete.
Argamassas com agregados alternativos: Potencialidade do emprego de areia de descarte de fundição e isoladores elétricos de porcelana Mortar with alternative aggregates: potential use of waste foundry sand and porcelain electrical insulator
In order to analyze the real behavior of the structure, the proof load test provides a very precise analysis of its actual behavior, because it is a test carried out on the structure, thus encompassing all the singularities that the structural element may have suffered during its manufacture and use that may affect its operation (failures in the design and execution of the structure, maintenance omission, incorrect use, exposure to bad weather, among others). The national standard NBR 9607 (ABNT, 2012) prescribes the use of load testing in the following situations: concerns about the quality of construction materials, inadequate use, or maintenance, or even a new use of the building, different from the one initially planned in the project. This study aims to present the most important criteria that must be considered in a load test. The procedures recommended by norms are exposed, highlighting the following topics: load test, load test guidelines, applied load intensity, how to apply the load, and the test evaluation criteria. On the basis of the theoretical foundation, a case study was made applying such criteria, analyzing its results, and defining the load to be supported by the structure analyzed.
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