Papers (estruturas em incêndio)

To design a steel structure in fire is necessary to know its temperature. Using the data from many experimental fire tests, Margaret Law estimated the maximum temperature in a compartment (natural fire), the external heat transfer to steel elements and the maximum temperature value for steel. The Eurocode adopted her method, with minor adjustments. The method is very calculation intensive—it involves about 60 equations— too many for a quick hand calculation. Besides, while a distinction is made between steel members engulfed and not engulfed in flame, the method is not clear about partially engulfed members. The authors developed the software ExteelFire to determine the maximum temperature of external steel structures for buildings in fire based on the Eurocode method including the determination of the temperature of the partially engulfed elements. Aiming to ascertain the level of safety of the Eurocode method, the results from ExteelFire and a numerical analysis performed using Smartfire (CFD software for the fire model) and Super Tempcalc (finite element method, FEM, software for the thermal analysis) were compared. Furthermore, results from ExteelFire and from two full-scale experimental tests (Dalmarnock and Ostrava) were contrasted. Based on the comparisons, the Eurocode method is conservative.

ABSTRACT The study of non-symmetrical composite columns is complex and European and North American standards only approach this issue superficially. In this text, a new proposal is presented for non-symmetrical composite column design subject to biaxial bending and axial compression, based on the compatibility of the deformation method, which considers the nonlinearity of the material with constitutive models according to Brazilian standards and geometric nonlinearity, as well as the equilibrium of the column in the displaced position. As a strategy for solving the general method, use is made of the "fiber element method", and for solving problems involving nonlinear equilibrium equations, the Newton-Raphson method.

The structural materials, as reinforced concrete, steel, wood and aluminum, when heated have their mechanical proprieties degraded. In fire, the structures are subject to elevated temperatures and consequently the load capacity of the structural elements is reduced. The Brazilian and European standards show the minimal dimensions for the structural elements had an adequate bearing capacity in fire. However, several structural checks are not contemplated in methods provided by the standards. In these situations, the knowledge of the temperature distributions inside of structural elements as function of time of exposition is required. The aim of this paper is present software developed by the authors called ATERM. The software performs the thermal transient analysis of two-dimensional structures. The structure may be formed of any material and heating is provided by means of a curve of temperature versus time. The data input and the visualization of the results is performed thought the GiD software. Several examples are compared with software Super TempCalc and ANSYS. Some conclusions and recommendations about the thermal analysis are presented.

EEn este trabajo se propusieron dos métodos, uno simplificado y otro gráfico alternativo para el diseño de la conexión mecánica tipo canal en vigas compuestas de hormigón y acero en situación de incendio, a partir del estudio de su comportamiento. Se utilizó como herramienta la modelación numérica. El método simplificado desarrollado considera temperaturas definidas a través de la modelación térmica del ensayo push-out en situación de incendio y es coherente con las expresiones de diseño de las conexiones mecánicas tipo canal a temperatura ambiente y la formulación existente para el diseño de las conexiones tipo perno a elevadas temperaturas. El método gráfico alternativo propuesto constituye una opción que permite obtener de una forma directa y rápida, la resistencia a elevadas temperaturas de la conexión mecánica tipo canal para un tiempo de resistencia al fuego, en función de su resistencia a temperatura ambiente.

En el trabajo se realiza el análisis térmico del ensayo push-out de conexiones tipo canal en estructuras compuestas acero – concreto a elevadas temperaturas a partir de resultados numéricos generados por el programa SuperTempcalc. El estudio se realiza para dos alternativas: vigas sin revestimiento contra incendio y vigas revestidas. Se proponen las temperaturas a considerar en el concreto para determinar los factores de reducción de su resistencia y se valora el impacto de estos resultados en la determinación de la resistencia de la conexión. Finalmente, se propone un método simplificado para determinar la resistencia de la conexión, que considera temperaturas en el concreto definidas a través del análisis térmico y es coherente con las expresiones de cálculo de la resistencia de las conexiones tipo canal a temperatura ambiente y con la formulación para conexiones tipo perno a elevadas temperaturas vigente en la literatura internacional.

En el trabajo se aborda el estudio de los factores que inciden en la resistencia, en situación de incendio, de las conexiones tipo perno en estructuras compuestas hormigón–acero con tipología de viga y losa maciza. Se realiza el diseño del experimento, la modelación térmica de los especímenes del ensayo push-out y el análisis de significación de diferentes parámetros en las relaciones de temperatura en secciones compuestas con vigas sin revestimiento y con revestimiento contra incendio. Por último, se proponen las temperaturas a considerar en el hormigón y el conector, expresadas como porcientos de la temperatura en el ala del perfil, para determinar los factores de reducción de la resistencia de la conexión en situación de incendio. Los resultados demuestran que los porcientos propuestos por EN 1994-1-2 (2005) para determinar la temperatura en el hormigón y el conector a partir de la temperatura en el ala no son válidos para todas las situaciones de diseño dentro del alcance del código.

The design of cold-formed steel structures is generally ruled by the ultimate buckling limit state. Most cold-formed steel profiles display open and rather thinwalled cross sections, which means that their structural behavior is strongly affected by buckling. On profiles with stiffened sections, such as C, Zee, rack and hat, there is the occurrence of distortional buckling. However, verifying distortional buckling is not trivial. According to the Brazilian standard, knowledge of the critical load that causes distortional buckling is necessary to design cold-formed steel profiles. Nevertheless, the code does not provide a procedure to obtain this critical load. This paper conducts a brief literature review of the distortional buckling mode and, by means of software for linear stability analysis, developed by the authors, presents the resistances associated with the distortional buckling of various cold-formed steel profiles, enabling structural elements design according to the Brazilian standard.

A análise de estruturas de aço conforme ABNT NBR 8800:2008 requer que a estrutura seja analisada considerando os efeitos de não linearidade geométrica por meio de análises mais precisas e também permite a utilização do método simplificado conhecido como método B1-B2. O objetivo deste artigo é avaliar um novo método simplificado, como alternativa ao método B1-B2, comparando os resultados obtidos aos métodos convencionais já existentes. Para a comparação do método simplificado proposto ao método P-∆, foi utilizado o programa computacional MASTAN2.

Examina-se a análise térmica do ensaio push - out de ligações tipo U a temperaturas elevadas a partir de resultados numéricos gerados pelo programa de computador Super Tempcalc. Estabelece-se que as relações entre a temperatura na base do conector e a temperatura da mesa do perfil (θsc/θf) e entre a temperatura do concreto e a temperatura da asa do perfil (θc/θf) para 0-30 minutos são notavelmente menores que as obtidas para a 0-90 minutos, assim como que as relações θc/θf são significativamente maiores quando a temperatura do concreto se determina a um quarto da altura do conector. Além disso, a altura e a largura do conector têm pouco impacto na relação θsc/θf, enquanto a altura do conector tem um impacto notável na relação θc/θf , e a influência da largura depende do nível onde se determina a temperatura do concreto.

Foram pesquisados alguns dos mais importantes países da América Latina e as informações sobre sua legislação são apresentadas no artigo

The Brazilian standards of structures in fire prescribe minimum dimensions for the ribbed slabs to ensure fire resistance. However, a new composite ribbed slab is not covered by any of the Brazilian standards in fire. The objective of this work is to present unpublished results from numerical and thermal analyses for this type of slab. Ribbed slabs filled with cell concrete blocks, ceramic bricks and EPS supported by cimentitious board were studied. The constructive element is considerate as thermal insulation if it has the capacity to prevent the occurrence, on the face non exposed to fire, temperature increments greater than 140 °C on the average or greater than 180 ºC at any point. The support function was determined limiting the temperature of the beams and slabs rebars to 500 ºC. The analyses were carried out with the ATERM and Super Tempcalc, software for two-dimensional thermal analysis by means of the finite element method. As a result, tables will be presented that link the fire resistance required time to slab dimensions and position of rebar. Prior to use in designing these results must be confirmed by experimental analysis, which is already being provided.

An essential component of a composite beam is the shear connection between the steel section and the concrete slab. Contrasting to the great quantity of push-out tests carried out at room temperature, a reduced number of push-out tests at elevated temperatures has been reported. Comparisons of temperature development in two different types of specimens are made between existing test results and numerical simulations using the finite element package SuperTempcalc. Values for the thermal properties of materials, the heat transfer coefficient and emissivity recommended in EN 1991-1-2 and EN 1994-1-2 were taken as essential references. The sensitivity of the calibrated model to variation in connector diameter and height is assessed, taking into account the defined scope of the formulations of the above mentioned codes. Also, different alternatives on the level at which should be considered the concrete temperatures are evaluated. The parametric numerical studies demonstrate that the connector height, the concrete compressive strength and the level in which the concrete temperature is considered, have a great influence on the resistance, specifically when concrete failure prevails against stud failure.