Dimensionamento de vigas de concreto armado em situação de incêndio: aprimoramento de algumas recomendações do Eurocode

Silva, Valdir Pignatta e

doi:10.1590/s1983-41952011000200007

Cited by 6 publications

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“…In this analysis, the closest reinforcement to the heated face was considered. It is worth mentioning that this is a foundation of the tabular method along with width beams and level load (Bolina et al, 2018;Silva, 2011).…”

Section: Parametric Analysis Resultsmentioning

confidence: 99%

“…It is worth mentioning that this is a foundation of the tabular method along with width beams and level load (Bolina et al. , 2018; Silva, 2011).…”

Section: Parametric Analysis Resultsmentioning

confidence: 99%

“…The divergence occurred close to the time when the temperature in the tensile flexural reinforcement reaches 500 8C. According to the tabular method, this temperature is considered critical for the safety of reinforced concrete structural elements (Bolina et al, 2018) (Silva, 2011), which is justified by the fact that, for temperatures higher than 500 8C, the steel of the reinforcement has practically no resistance, failing to contribute to the strength of the reinforced concrete element. It is worth mentioning that the critical steel of 500 8C temperature corresponds approximately to the combinations of actions in fire conditions is 70% of combinations of actions in normal conditions.…”

Section: Trf Of Reinforced Concrete Beamsmentioning

confidence: 99%

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Evaluation of the TRF of reinforced concrete beams through thermal and thermostructural analysis

Nicoletti

Oliveira

Souza

et al. 2023

JSFE

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PurposeIn the analysis of structures in a fire situation by simplified and analytical methods, one assumption is that the fire resistance time is greater than or equal to the required fire resistance time. Among the methodologies involving the fire resistance time, the most used is the tabular method, which associates fire resistance time values to structural elements based on minimum dimensions of the cross section. The tabular method is widely accepted by the technical-scientific community due to the fact that it is safe and practical. However, its main criticism is that it results in lower fire resistance times than advanced thermal and thermostructural analysis methods. The objective of this study was to evaluate the fire resistance time of reinforced concrete beams and compare it with the required fire resistance time recommended by the tabular method of NBR 15200 (ABNT, 2012).Design/methodology/approachThe fire resistance time and required fire resistance time of reinforced concrete beams were evaluated using, respectively, numerical models developed based on the finite element method and the tabular method of NBR 15200 (ABNT, 2012). The influence of the following parameters was investigated: longitudinal reinforcement cover, characteristic compressive strength of concrete, beam height, longitudinal reinforcement area and arrangement of steel bars.FindingsAmong the evaluated parameters, the covering of the longitudinal reinforcement proved to be more relevant for the fire resistance time, justifying that the tabular method of NBR 15200 (ABNT, 2012) being strongly and directly influenced by this parameter. In turn, more resistant concretes, higher beams and higher steel grades have lower fire resistance time values. This is because beams in these conditions have greater resistance capacity at room temperature and, consequently, are subject to external stresses of greater magnitude. In some cases, the fire resistance time was even lower than the required fire resistance time prescribed by NBR 15200 (ABNT, 2012). Both the fire resistance time and the required fire resistance time were not influenced by the arrangement of the longitudinal reinforcements.Originality/valueThe present paper innovates by demonstrating the influence of other important design variables on the required fire resistance time of the NBR 15200 (ABNT, 2012). Among several conclusions, it was found that the load level to which the structural elements are subjected considerably affects their fire resistance time. For this reason, it was recommended that the methods for calculating the required fire resistance time consider the load level. In addition, the article quantifies the security degree of the tabular method and exposes some situations for which the tabular method proved to be unsafe. Moreover, in all the models analyzed, the relationship between the span and the vertical deflection associated with the failure of the beams in a fire situation was determined. With this, a span over average deflection relationship was presented in which beams in fire situations fail.

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Section: Parametric Analysis Resultsmentioning

confidence: 99%

“…It is worth mentioning that this is a foundation of the tabular method along with width beams and level load (Bolina et al. , 2018; Silva, 2011).…”

Section: Parametric Analysis Resultsmentioning

confidence: 99%

Section: Trf Of Reinforced Concrete Beamsmentioning

confidence: 99%

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Evaluation of the TRF of reinforced concrete beams through thermal and thermostructural analysis

Nicoletti

Oliveira

Souza

et al. 2023

JSFE

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“…When dimensioning reinforced concrete beams by the tabular method, [19] points out that the following hypotheses are admissible: (a) beams under slabs, which promote their heat on three surfaces only, (b) moment redistribution, as for continuous beams, and (c) critical temperature of bottom longitudinal reinforcements equals to 500°C. In order to define the strength reduction factors of materials subjected to high temperatures, [19] states that NBR 15200 relied on old correlations, presented in Equations (1) for steel, depicted as graphs in the standard. The strength reduction factors of reinforcements are used in the simplified and advanced methods as well.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the assessment methods of reinforced concrete beams in fire conditions proposed by NBR 15200

Bolina

Baques

Tutikian

et al. 2018

Rev. IBRACON Estrut. Mater.

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In Brazil, reinforced concrete structures designed based on NBR 6118 [1] must be assessed in fire conditions through NBR 15200 [2], which proposes multiple test methods. Concerning beams, this standard offers the tabular and simplified methods as possible choices. This study aimed to compare these two methods by applying their principles to isostatic and hyperstatic beams with section of 20x50 cm, designed at room temperature according to NBR 6118 [1]. The temperature distribution along sections was obtained by means of a software program. The results from this study indicated that the simplified method yielded higher fire-resistance ratings (FRR) in 75% of cases, although not surpassing the tabular method by 30 minutes. The simplified method allowed an optimization of the results, despite the longer design time.

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“…Estudou-se a possibilidade de redução do c 1 em casos em que haja reserva de segurança e, também, o aumento de c 1 lateral em algumas situações. Mais tarde, incorporaram-se as informações apresentadas emSilva (2010Silva ( , 2011 à versão atualizada da norma, a ABNT NBR 15200:2012. Dissertação.…”

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Dimensionamento de vigas de concreto armado em situação de incêndio.

Albuquerque¹

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criaram-se gráficos que associam o parâmetro µ, relação entre o momento fletor solicitante em situação de incêndio e o momento fletor resistente à temperatura ambiente, ao tempo de resistência ao fogo (TRF), para cada situação de interesse. Esses gráficos, que envolvem tanto armaduras positivas quanto negativas, também permitem levar em conta a redistribuição de momentos, o que conduzirá à otimização na solução encontrada. Nos exemplos de aplicação realizados, os resultados obtidos a partir do método gráfico se mostraram, em geral, mais econômicos, quando comparados aos do método tabular. Palavras-chave: Concreto armado. Vigas. Dimensionamento. Incêndio. Análise térmica. Método gráfico. ABSTRACTReinforced concrete beams lose their load capacity when subjected to fire. The most practical tool for their design is the tabular method, presented in ABNT NBR 15200:2012, in which, from the time required for fire resistance (TRRF), the minimum width of the transversal section and the smallest admissible distance between the centroid of the rebar and the heated face can be found. Yet, albeit simple, it limits the calculation to a few fixed values, not allowing the engineer to seek different solutions.Hence, an alternative method was developed in this Dissertation, using the Swedish Super Tempcalc software. Firstly, the temperature field of beams subjected to ISO 834 (1999) standard fire situation was defined, as a function of time. Next, considering the reduction in concrete and steel strength, the resistance bending moment was calculated for the different cases studied. Beams with different widths, heights, covers, diameters and reinforcing bars dispositions were thermally and structurally analyzed. The resistance moments in fire situation obtained from the software were compared to values deriving from simplified methods, proposed by Brazilian and European (Eurocode 2 part 1-2, 2004) standards, besides a more advanced method. After data validation, graphs were created, associating the parameter µ, ratio between the applied bending moment in fire and the resistance bending moment at ambient temperature, to time for fire resistance (TRF), for each situation of interest. These graphs, involving both positive and negative reinforcement, also allow consideration of the redistribution of moments, which will lead to the optimization of the solution found. In the examples analyzed, the results deriving from the graphic method were generally more economic compared to the tabular method.

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Dimensionamento de vigas de concreto armado em situação de incêndio: aprimoramento de algumas recomendações do Eurocode

Cited by 6 publications

References 0 publications

Evaluation of the TRF of reinforced concrete beams through thermal and thermostructural analysis

Evaluation of the TRF of reinforced concrete beams through thermal and thermostructural analysis

Analysis of the assessment methods of reinforced concrete beams in fire conditions proposed by NBR 15200

Dimensionamento de vigas de concreto armado em situação de incêndio.

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