Axial buckling load of partially encased columns under fire

Mestrado em cooperação com a Hassiba Benbouali University of ChlefPartially encased columns have significant fire resistant. However, it is not possible to assess the fire resistance of such members simply by considering the temperature of the steel. The presence of concrete increases the mass and thermal inertia of the member and the variation of temperature within the cross section, in both the steel and concrete components. The annex G of EN1994-1-2 allows to calculate the load carrying capacity of partially encased columns, for a specific fire rating time, considering the balanced summation method. New formulas will be used to calculate the plastic resistance to axial compression and the effective flexural stiffness. These two parameters are used to calculate the buckling resistance. The finite element method is used to compare the results of the elastic critical load for different fire ratings of 30 and 60 minutes. The buckling resistance is also calculated by the finite element method, using an incremental and iterative procedure. This buckling resistance is also compared with the simple calculation method, evaluating the design buckling curve that best fits the results.As colunas parcialmente embebidas com betão possuem elevada resistência ao fogo. No entanto, não é possível avaliar a resistência ao fogo de tais elementos simplesmente considerando a evolução da temperatura do aço. A presença de betão aumenta a massa, a inércia térmica do elemento e a variação de temperatura dentro da seção transversal, tanto no aço como nos componentes de betão. O anexo G da EN1994-1-2 permite calcular a capacidade resistente de colunas parcialmente embebidas com betão, para um tempo específico resistência ao fogo, considerando o método da soma pesada das componentes. Novas fórmulas serão utilizadas para calcular a resistência plástica à compressão axial e a rigidez à flexão efetiva. Estes dois parâmetros são utilizados para calcular a resistência à encurvadura. O método dos elementos finitos é utilizado para comparar os resultados da carga crítica elástica para diferentes classificações de resistência ao fogo, 30 e 60 minutos. A resistência à encurvadura também é calculada pelo método dos elementos finitos, por um processo incremental e iterativo. A resistência à encurvadura é também comparada com o método de cálculo simplificado, avaliando a curva de encurvadura que melhor se ajusta aos resultados

Non-linear buckling analysis of composite columns made from high and normal strength concrete under fire

Composite structures made from the combination of steel profile and concrete have significant loadbearing capacity which depends on the behaviour of the two material components and their interaction, particularly in fire conditions. It is not possible to assess the fire resistance of composite members only by considering the temperature of the steel, because the presence of the concrete may contribute greatly to increase the resistance, strength and thermal inertia of the member, which improves consequently the fire behaviour of the element. The aim of this work is to develop an efficient non-linear 3D finite element model to investigate the behaviour of pin-ended axially loaded composite column made from high strength concrete (HSC) and normal strength concrete (NSC) at different fire rating classes. Two types of column section were selected, notably HEB 160 profile totally encased with concrete and HEB220 partially encased with concrete. The fire behaviour of the columns was tested according to ISO834 standard fire. The results show that the use of HSC in composite columns reduces the level of fire protection with the regard to NSC. NSC in composite structures accommodates higher deflections than HSC, which is safer in case of fire accident. The mechanical resistance in composite columns at room temperature is reduced more than twice after 30 min of fire exposure.info:eu-repo/semantics/publishedVersio

Stability of partially encased columns under fire

The stability of partially encased columns under fire is evaluated, based on two different methods. The simple calculation method is presented and depends on new simple formulae, based on two major hypotheses, safer than the current method proposed in EN1994-1-2. This document establishes a designing method that considers the contours of temperature within the cross section after 30, 60, 90 and 120 minutes under fire exposure. The cross section is divided into four components in which the mechanical property of the material changes with the average temperature and part of the material is also neglected. An advanced calculation method, fully three-dimensional, is used to compare the results of the axial critical load. The results agree very well for fire ratings of 30 and 60 minutes.info:eu-repo/semantics/publishedVersio

Axial buckling resistance of partially encased columns

Partially Encased Columns (PEC) present good axial buckling resistance under fire, mainly due to the presence of concrete between flanges. The presence of concrete increases the mass and thermal inertia of the member and changes the variation of the temperature field within the cross section, in both the steel and concrete. The elastic buckling load of PEC under fire conditions may be calculated by the balanced summation method and by the finite element method. This work compares the results from both solution methods and provides the validation of the three dimensional model for different fire ratings of 30 and 60 minutes.info:eu-repo/semantics/publishedVersio

Load carrying capacity of partially encased columns for different fire ratings

Partially encased columns have significant fire resistant. However, it is not possible to assess the fire resistance of such members simply by considering the temperature of the steel. The presença of concrete increases the mass and thermal inertia of the member and the variation of temperatures within the cross section, in both the steel and concrete components. The annex G of EN 1994-1-2 [1] allows to calculate the load carrying capacity of partially encased columns, for a specific fire rating time, considering the balanced summation method. New formulas will be used to calculate the plastic resistance to axial compression and the effective flexural stiffness. These two parameters are used to calculate the buckling resistance, assuming the most appropriate buckling curve of EN1993-1-1 [2]. The fínite element method is used to determine which curve best fits the buckling resistance for different fire ratings of 30, 60, 90 and 120 minutes.info:eu-repo/semantics/publishedVersio

Fire performance of composite columns Made from high and normal strength concrete: influence of thermal and mechanical parameters

Composite structures made from the combination of steel profile and concrete have significant load bearing capacity which depend on the behaviour of the two materials and their interaction, particularly in fire conditions. It is not possible to assess the fire resistance of composite members only by considering the temperature of the steel, because the presence of concrete may contribute greatly to increase the mass and thermal inertia of the member, which improve the fire behaviour of the element. The aim of this work is to develop an efficient Non-linear 3-D finite element model to examine the behaviour of Pin-ended axially loaded composite columns made from High Strength Concrete (HSC) and Normal Strength Concrete (NSC) for different fire ratings of 30, 60, 90 and 120 minutes. Two types of column were selected to investigate the effect of fire, notably HEB profile ranging from 160 to 200 encased with concrete partially or totally (PEC, TEC). These columns were tested under ISO834 fire standard. The critical load has been compared for columns height of 3 m, pinned in both ends. Properties for steel profile and reinforcement were assumed from S275 grade and B500 grade respectively, while C20/25 and C80/95 (NSC; HSC) was assumed for concrete. The results found show that the use of HSC in composite columns reduces the level of fire protection with the regard to NSC.info:eu-repo/semantics/publishedVersio

Fire resistance of partially encased composite columns subjected to eccentric loading

Purpose – Investigate the fire performance of eccentrically loaded concrete partially encased column (PEC), using the advanced calculation method (ANSYS 18.2, 2017) and the simple calculation method in Annex G of Eurocode 4 (EN 1994-1-2, 2005). This work examines the influence of a range of parameters on fire behaviour of the composite column including: eccentricity loading, slenderness, reinforcement, fire rating and fire scenario. In this study, ISO-834 (ISO834-1, 1999) was used as fire source. Design/methodology/approach – Currently, different methods of analysis used to assess the thermal behaviour of composite column exposed to fire. Analytical method named simplified calculationmethods defined in European standard and numerical simulations named advanced calculation models are treated in this paper. Findings – The load-bearing capacity of the composite column becomes very weak in the presence of the fire accident and eccentric loading, this recommends to avoid as much as possible eccentric loading during the design of construction building. The reinforcement has a slight influence on the temperature evolution; moreover, the reinforcement has a great contribution on the load capacity, especially in combined compression and bending. When only the two concrete sides are exposed to fire, the partially encased composite column presents a high load-bearing capacity value. Originality/value – The use of a three-dimensional numerical model (ANSYS) allowed to describe easily the thermal behaviour of PEC columns under eccentric loading with the regard to the analytical method, which is based on three complex steps. In this study, the presence of the load eccentricity has found to have more effect on the load-bearing capacity than the slenderness of the composite column. Introducing a load eccentricity on the top of the column may have the same a reducing effect on the load-bearing capacity as the fire.info:eu-repo/semantics/publishedVersio

Fire performances of partially encased column subjected to eccentric loading

In this paper, the advanced and simplified calculation methods are used to evaluate the fire resistance of eccentrically loaded partially encased composite columns (PEC). The work consists in developing an efficient Non-linear 3-D finite element model (ANSYS) to investigate the behaviour of Pin-ended PEC eccentrically loaded at elevated temperature. The columns were tested under standard ISO834 fire. The buckling load is determined for several column heights 3; 4.5 and 6 m, by considering an eccentricity around the minor axis equal to 0,5.B ; 1,0.B and 1,5.B (B base). The numerical method presented here is compared with the simple calculation method Annex G of EN 1994-1-2. The results show that after 50 min of fire exposure, the axial load capacity of PEC is reduced to more than half, which is a fair conclusion to take into consideration in structural fire design. The comparison results show a good agreement between the two methods at high fire ratings (R90 and R120), however at low fire rating (R30), the simple calculation method presents conservative results. It is to be concluded that the eccentricity of loading reduces the loadbearing capacity of the composite column. The shortest column (3m) presents the higher reduction in load bearing.info:eu-repo/semantics/publishedVersio

Fire performances of partially encased column subjected to eccentric loading

In this paper, the advanced and simplified calculation methods are used to evaluate the fire resistance of eccentrically loaded partially encased composite columns (PEC).info:eu-repo/semantics/publishedVersio

Behaviour of industrial buildings with steel portal frames under fire conditions

Pitched roof Steel frame structures are widely used in industrial buildings for practical reasons of exploitation, durability and cost efficiency. However, steel being a ductile material, it remains vulnerable to excessive temperatures. The recent accidents, which occurred in the industrial buildings of Sonatrach (petroleum industry in Algeria), in an urban area in Algiers or in an industrial zone in Skikda, remind us of the real danger and the potential risk of fire.info:eu-repo/semantics/publishedVersio