The load-bearing of composite slabs with steel deck under natural fires

Composite slabs with steel deck combine the load-bearing resistance of the steel deck and rebar with the compressive resistance of the concrete (components). Unprotected composite slabs may be exposed to natural fire conditions from below, and steel reduces its load-bearing capacity during the heating stage. In short fire events, with limited deformations, the composite slabs can recover the load-bearing capacity during the cooling stage. This research presents the validation of the numerical model and the development of a parametric study, to evaluate the load-bearing capacity during the fire event. This method includes a time step procedure, based on the average temperature calculation for each component, including the reduction coefficients applied to the design strength of each material. A new proposal is also presented to evaluate the residual loadbearing capacity. In some circumstances, the residual load-bearing can be reduced by more than 20%. The results showed that the highest variation in the load-bearing resistance of composite slabs occurs when the steel temperatures are between 20 and 600 ℃, after this temperature, the steel has already lost most of its mechanical strength. Moreover, it was observed that different heating rates and different cooling rates influence the rate of the reduction and recovery of the load-bearing capacity. It was also noticed that the lowest load-bearing capacity of the composite slabs was reached after the end of the heating phase, showing that the stability of the element during the heating phase does not guarantee fire safety during the cooling phase.info:eu-repo/semantics/publishedVersio

A new calculation method for the temperature of the components of composite slabs under fire

Composite steel-concrete slabs are structural elements composed of a profiled steel deck which acts as a permanent formwork to the concrete topping. This layer is commonly reinforced with individual rebars and an anti-crack mesh. The Annex D of the EN 1994-1-2 provides guidelines for the calculation of the temperature of the steel components of composite slabs subjected to the standard fire. However, no revisions were made to these calculation rules during the last years. This paper proposes a new method for the estimation of the temperature of the parts of the steel deck and the rebars as well. The proposed methodology is derived from numerical analyses using a 3-D finite element model, considering perfect thermal contact between the materials.info:eu-repo/semantics/publishedVersio

Experimental tests and numerical simulation of fire fighter clothing exposed to radiant heat

Neste artigo é apresentado um estudo de avaliação do comportamento de um conjunto muito significativo, de tecidos para proteção individual de segurança de bombeiros, quando submetidos a uma fonte de calor radiante. São apresentados ensaios experimentais desenvolvidos na Universidade de Tsinghua (TU, China) e no Instituto Politécnico de Bragança (IPB, Portugal). São apresentados os resultados de 84 ensaios experimentais no IPB, sendo 72 ensaios realizados para baixos níveis de fluxo de calor incidente (5 [kW/m2]) e 12 ensaios realizados para níveis médios de fluxo de calor incidente (20 kW/m2]). Estes ensaios permitiram determinar qual a melhor combinação de proteção para diferentes conjuntos de materiais com 3 camadas (camada exterior com 6 tecidos diferentes, barreira térmica com 4 tecidos diferentes e camada interior com 3 tecidos diferentes). A melhor combinação foi determinada pelo conjunto de material que apresentava menor densidade de fluxo de calor transmitido (TB3/BT2/F1 para baixos níveis de densidade de fluxo radiante e TB1/BT2/F1 para níveis médios de densidade de fluxo radiante). É ainda apresentado um estudo numérico 2D, não linear transiente, para baixos e médios níveis de densidades de fluxo de calor incidente. O modelo numérico foi validado com os ensaios realizados na Universidade de Tsinghua. Estes resultados permitiram concluir que existe uma relação não linear entre o fluxo de calor incidente e o fluxo de calor transmitido, tendo em consideração o estudo paramétrico.This paper presents the results of a very significant number of radiant heat tests on different fabrics assemblies for individual fire safety protection. Experimental tests developed at Tsinghua University (TU, China) and at the Polytechnic Institute of Bragança (IPB, Portugal) are presented. A total of 84 experimental tests were carried out at IPB, of which 72 were performed for low incident heat flux level (5 [kW/m2]) and 12 tests for medium incident heat flux level (20 [kW/m2]). These tests allowed to determine the best combination of protection for different assemblies of materials with 3 layers (outer layer with 6 different fabrics, thermal barrier with 4 different fabrics and inner layer with 3 different fabrics). The best combination was determined by the assembly with the lowest transmitted heat flux density (TB3/BT2/F1 for low radiation level and TB1/BT2/F1 for the medium radiation level). A two-dimensional nonlinear transient numerical model for low and medium incident heat flux is also presented. The numerical model was validated with the experimental tests performed at Tsinghua University. These results led to the conclusion that there is a nonlinear relationship between the incident heat flux and the transmitted heat flux, based on the parametric study.info:eu-repo/semantics/publishedVersio

Estimating the temperature on the reinforcing bars of composite slabs under fire conditions

A three-dimensional computational model based on finite elements was developed to evaluate the thermal behaviour of composite slabs with steel deck exposed to a standard fire. The resulting numerical temperatures are then used to obtain a new analytical method, which is an alternative to the simplified method provided by the standard, to accurately determine the temperatures at the reinforcing bars (rebar). The fitting of the analytical model to the numerical data was done by solving a linear least squares problem using the singular value decomposition. The resulting formula fits very well the numerical data, allowing to make predictions of the temperature in the rebar with an approximation error equal to zero and an estimating error at least 77% lower than that obtained with the proposal included in the standard.info:eu-repo/semantics/publishedVersio

Computational simulation of the thermal effects on composite slabs under fire conditions

A computational model is presented to evaluate the thermal effects on composite slabs with still deck, originated by standard fire exposure. Composite slabs with profiled steel deck are widely used in buildings which require fire resistance. Computational simulations are of great importance in this field and consist of an alternative to experimental fire tests that are expensive, time-consuming and require semi-specialized technical equipment. However, computational simulations must be reliable and realistic. The resulting transient and non-linear thermal problem is solved by the Finite Element Method in ANSYS and Matlab. The finite element models are three-dimensional, full scale, and multi-domain. Additionally, the models also include an air gap between the steel deck and the concrete part of the slab, in order to simulate the thermal effects induced by the debonding between the steel deck and the concrete, verified in previous experimental investigations. The results of the numerical simulations are validated against the results of experimental fire tests. The fire resistance of the composite slabs determined computationally is also compared with simplified calculation methods available in standards.info:eu-repo/semantics/publishedVersio

Thermal buckling of railways

This manuscript presents the results of numerical research regarding the thermal buckling on railway tracks. High temperatures may cause thermal buckling on the railways and due to this fact speed restrictions are often issued to reduce the probability of derailments. Railways are subject to thermal and mechanical loads in which, given some circumstances, buckling may take place. Continuous welded rail (CWR) is more prone to this effect than jointed rails since the longitudinal displacement is restrained. This research is focused on the effect of the track gauge, rail profile, initial imperfection amplitude, sleeper's elasticity modulus, torsional resistance of fastenings, and ballast resistance on the thermal buckling of railways. A total of 144 simulations were developed, concluding that the imperfection level and ballast resistance are the most affecting parameters on the buckling temperature.info:eu-repo/semantics/publishedVersio

Fire resistance of composite slabs with steel deck under natural fire

Most 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. Three-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. The 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. The 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.info:eu-repo/semantics/publishedVersio

Prediction models for rail temperatures validated with experimental measurements

Rail temperatures play an important role when understanding and predicting rail track’s instabilities. An energy balance model called CNU was used to simulate rail temperatures, validated with FEA analysis, and compared with field-collected data. The model uses weather data and accounts for the solar position to improve temperature prediction. In addition, a python package is developed to solve the thermal lumped model including specific modifications on the model. Both simplified and Finite Element Analysis (FEA) models are in good agreement. Compared with the collected data, the model reaches an R² of 0.914.info:eu-repo/semantics/publishedVersio