Fire Resistance Of Composite Slabs Research Articles

Improved tensile membrane action model of composite slabs at elevated temperatures

Previous fire testes have showed that tensile membrane action (TMA) between composite slabs and reinforced concrete slabs is different. An improved TMA model is proposed in this paper to accurately and reasonably determine the fire resistance of composite slabs exposed to ISO834 fire. It is assumed that the fracture of steel reinforcement in the long span is the governing failure mode of composite slabs at elevated temperatures. The slab is divided into four concrete rigid plates and one elliptic reinforcement net at centre considering TMA, and the contribution of rotation of concrete rigid plates on the deflection in short-span is taken into account. Meanwhile, coupling thermo-mechanical finite element analyses are carried out to simulate the TMA response of composite slabs at elevated temperatures. The accuracy of the proposed improved model is validated against experimental and numerical results, with a maximum error within 10%. It is found that the improved model has a better prediction of the mid-span deflection and fire resistance than Li’s model and Bailey’s model. It is important to consider the stress redistribution of the reinforcement in two directions in determining TMA in composite slabs under fire conditions.

Fire resistance of composite slabs with steel deck under natural fire

PurposeMost of the numerical research and experiments on composite slabs with a steel deck have been developed to study the effect of fire during the heating phase. This manuscript aims to describe the thermal behaviour of composite slabs when submitted to different fire scenarios, considering the heating and cooling phase.Design/methodology/approachThree-dimensional numerical models, based on finite elements, are developed to analyse the temperatures inside the composite slab and, consequently, to estimate the fire resistance, considering the insulation criteria (I). The numerical methods developed are validated with experimental results available in the literature. In addition, this paper presents a parametric study of the effects on fire resistance caused by the thickness of the concrete part of the slab as well as the natural fire scenario.FindingsThe results show that, depending on the fire scenario, the fire resistance criterion can be reached during the cooling phase, especially for the thickest composite slabs. Based on the results, new coefficients are proposed for the original simplified model, proposed by the standard.Originality/valueThe developed numerical models allow us to realistically simulate the thermal effects caused by a natural fire in a composite slab and the new proposal enables us to estimate the fire resistance time of composite slabs with a steel deck, even if it occurs in the cooling phase.

Influence of load-level and effective thickness on the fire resistance of composite slabs with steel deck

Composite slabs with steel deck have been used on building construction due to its fast-and-easy crafting that brings economic outstanding alternatives to architects and engineers on large-scale steel framed constructions. At room temperatures and in Europe, the designing procedures of composite slabs are defined by Eurocode 1994-1-1. When it comes to the fire safety analysis of these elements, the designing procedure requires more attention due to the direct exposition of the steel deck to fire, affecting the overall bending resistance. This importance is presented in Eurocode 1994-1-2, taking in consideration the integrity, insulation and load-bearing criteria. In this work the thermal and mechanical behaviour of composite slabs with steel deck exposed to standard fire ISO 834 are studied through numerical simulations using Finite-Element Method (FEM). The model was previously validated with one experimental test from literature. The ANSYS Mechanical APDL software was used to develop a parametric study, simulating four different geometries with different load levels, comprehending a total of 126 thermal and mechanical simulations used to determine the correlation between load-level and fire resistance. As result, a new simplified method is proposed for the load bearing fire resistance of composite slabs, considering the effect of the effective thickness and the load level. The fire resistance decreases with the load level and increases with the thickness of the concrete. A new proposal is presented to determine the fire resistance, based on these two parameters.

An insight into eurocode 4 design rules for thermal behaviour of composite slabs

Closed-form calculation rules for thermal responses of composite slabs with profiled steel decking are provided in EC4, which are only applicable to a specified range of slab geometries available in the 1990s and are unchanged for two decades. This paper aims to gain an insight into the thermal behavior of composite slabs, and to investigate the applicability of EC4 calculation rules to a wider practical range nowadays (usually beyond the specified range). Parametric studies are conducted to study the influence of moisture content and slab geometry on the temperature distribution in composite slabs. The results show that the calculation methods in EC4 are not applicable to composite slabs with geometries beyond the specified range. It is found that the insulation-based fire resistance of composite slabs is governed by the maximum temperature rather than the average temperature. The EC4 calculations overestimate the fire resistance and a reduction factor of 15% is recommended. The moisture content has a significant effect on the temperature distribution in composite slabs, and improvement to EC4 is proposed by considering its the effect in a rate of 5 min per 1% increase of moisture content. Tabulated results are given to determine the temperature of reinforcement in the thin portion and temperature distribution in the composite slabs.

Effect of the load level on the resistance of composite slabs with steel decking under fire conditions

The fire resistance of composite slabs with steel decking, in Europe, is usually defined using simple calculation models provided by the Eurocode EN 1994-1-2. For assessing the methodology of these simple calculation methods, a new advanced calculation method is presented, using the software ANSYS. The numerical model is first validated with experimental data reported on bibliography and then a parametric analysis is conducted to better understand the effect of the load level on the composite structure under fire. The validation of the simulations consisted of three different models: the first model considers perfect contact between the steel deck and the concrete topping, and the two following models consider the existence of an air gap between these materials, acting as a thermal resistance on the temperature field through the thickness of the slab. The numerical results show good approximation to the experimental results, mainly when using the non-perfect contact model, reaching 3.88% and 16.91% of difference with respect to the insulation and load-bearing criteria, respectively. Based on the validation models, a parametric study is presented, modifying the load level from 10% up to 75%. New simple calculation models are presented to define the fire resistance of composite slabs, considering the load level, and the debonding effect between the concrete and the steel deck.

Improved Calculation Method for Insulation-based Fire Resistance of Composite Slabs

Abstract Floor slabs play a critical role in the fire resistance of buildings, not only by maintaining structural stability and integrity, but also by providing thermal insulation to limit the rise in temperature of floors above a fire. Composite slabs, consisting of concrete topping on steel decking, are common in steel building construction, but the profiled geometry of the decking makes the analysis of heat transfer in composite slabs more complex than for flat slabs. A method for calculating the insulation-based fire resistance of composite slabs with profiled steel decking is provided in Annex D of Eurocode 4 (EC4). However, the applicability of the EC4 calculation method is limited to a range of commonly used slab geometries from the 1990s, which is narrower than the range used in current practice. In addition, the EC4 calculation method assumes a specific value of moisture content for the concrete, and different values of moisture content can significantly affect the fire resistance, as shown in this study. This paper proposes an improved algebraic expression for estimation of the insulation-based fire resistance of composite slabs that explicitly accounts for moisture content and is applicable to an extended range of slab geometries. The proposed expression is developed based on computed values of fire resistance obtained from a validated finite element modeling approach. A set of 54 composite slab configurations are selected for analysis using a sequential experimental design. The accuracy of the proposed method is verified against numerical results for an additional set of 32 slab configurations and is also validated against experimental data. Comparisons of the proposed calculation method with the results of the verification analyses show deviations of less than 15 min in all cases for the insulation-based fire resistance of the composite slabs.

Improved calculation method for insulation-based fire resistance of composite slabs

Floor slabs play a critical role in the fire resistance of buildings, not only by maintaining structural stability and integrity, but also by providing thermal insulation to limit the rise in temperature of floors above a fire. Composite slabs, consisting of concrete topping on steel decking, are common in steel building construction, but the profiled geometry of the decking makes the analysis of heat transfer in composite slabs more complex than for flat slabs. A method for calculating the insulation-based fire resistance of composite slabs with profiled steel decking is provided in Annex D of Eurocode 4 (EC4). However, the applicability of the EC4 calculation method is limited to a range of commonly used slab geometries from the 1990s, which is narrower than the range used in current practice. In addition, the EC4 calculation method assumes a specific value of moisture content for the concrete, and different values of moisture content can significantly affect the fire resistance, as shown in this study. This paper proposes an improved algebraic expression for estimation of the insulation-based fire resistance of composite slabs that explicitly accounts for moisture content and is applicable to an extended range of slab geometries. The proposed expression is developed based on computed values of fire resistance obtained from a validated finite element modeling approach. A set of 54 composite slab configurations are selected for analysis using a sequential experimental design. The accuracy of the proposed method is verified against numerical results for an additional set of 32 slab configurations and is also validated against experimental data. Comparisons of the proposed calculation method with the results of the verification analyses show deviations of less than 15 min in all cases for the insulation-based fire resistance of the composite slabs.

Numerical simulation of the fire resistance of composite slabs with steel deck

This investigation is related with the fire resistance of composite slabs with steel deck. This composite solution consists of a concrete topping cast on the top of a steel deck. The concrete is typically reinforced with a steel mesh and may also contain individual rebars. The deck also acts as reinforcement and may be exposed to accidental fire conditions from the bottom. This composite solution is widely used in every type of buildings and requires fire resistance, in accordance to regulations. The fire resistance is specified by the loadbearing capacity (R), insulation (I) and integrity (E). The fire rating for (R) and (E) is not in the scope of this investigation. The fire rating for insulation (I) is evaluated by two different methods (numerical simulation and simple calculation). The fire rating is calculated for 32 different geometric configuration, in order to evaluate the effect of the thickness of the concrete layer and the thickness of steel deck. The fire resistance (I) increases with the thickness of the concrete when using both methods, but the simple calculation method seems to be unsafe for all the cases, requiring a revision for the formulae presented in Annex D of EN1994-1-2. A new proposal is presented.

Thermal performance of composite slabs with profiled steel decking exposed to fire effects

This paper presents a systematic investigation of the influence of various parameters on the thermal performance of composite floor slabs with profiled steel decking exposed to fire effects. The investigation uses a detailed finite-element modeling approach that represents the concrete slab with solid elements and the steel decking with shell elements. After validating the modeling approach against experimental data, a parametric study is conducted to investigate the influence of thermal boundary conditions, thermal properties of concrete, and slab geometry on the temperature distribution within composite slabs. The results show that the fire resistance of composite slabs, according to the thermal insulation criterion, is generally governed by the maximum temperature occurring at the unexposed surface of the slab, rather than the average temperature. The emissivity of steel has a significant influence on the temperature distribution in composite slabs. A new temperature-dependent emissivity is proposed for the steel decking to give a better prediction of temperatures in the slab. The moisture content of the concrete has a significant influence on the temperature distribution, with an increment of 1% in moisture content leading to an increase in the fire resistance of about 5 min. The height of the upper continuous portion of the slab is found to be the key geometrical factor influencing heat transfer through the slab, particularly for the thin portion of the slab. Heat transfer through the thick portion of the slab is also significantly affected by the height of the rib and the width at the top of the rib.

Advanced Modeling of Composite Slabs with Thin-Walled Steel Sheeting Submitted to Fire

The paper studies the behavior of composite slabs with corrugated steel sheeting at elevated temperatures. Two structural systems are considered: a simply supported composite slab and a continuous composite slab that consists of two equal spans. Both of them are designed according to the respective Eurocodes to have similar strengths at room temperature. In the sequel, sophisticated three-dimensional models of the slabs are developed. Coupled thermo-mechanical analysis is used, which takes into account the various nonlinearities that are present in the physical model (dependence of the thermal and mechanical properties of the material on temperature, nonlinear material behavior, cracking etc.). The results of the thermal analysis are compared with the temperature field that is proposed in Eurocode 4. For both the structural systems, the fire resistance, in time domain, that yields from the coupled analysis is compared with the fire resistance that results following the provisions of Eurocode 4. Another objective is to evaluate the effect of static indeterminacy on the fire resistance of composite slabs.

Fire resistance of composite slabs

Composite slabs are slabs in which profiled steel sheeting acts as a permanent formwork and as reinforcement to the concrete placed on top. During fire the sheeting heats up and loses strength. However, tests have shown that due to the heat absorbed by the concrete, the performance is better than that of unprotected steel and that fire resistance of composite slabs is at least 30 minutes. For fire ratings of 60 minutes or beyond, additional measures usually have to be taken, of which the application of additional reinforcement is usually the most economical. Recommendations were established by the ECCS in 1983, enabling a quick and simple calculation of the fire resistance of composite slabs to be made. These recommendations were taken as a basis for Eurocode 4-Part 1.2. ‘Structural Fire Design’. This paper describes the calculation method of EC 4 and considers some new research developments that could be implemented in newer versions of the Eurocode, leading to a more economic design of composite slabs.