Fire Protection Thickness Research Articles

A Model generation method and iteration algorithm for optimising fire protection thickness

With temperatures rising above 1000 °C within 5 min, hydrocarbon fire causes rapid strength degradation of structural steel members. It is among the most dangerous hazards, such as boiling liquid expanding vapour explosion (BLEVE) in the oil and gas industry. Intumescent coating as passive protection is widely adopted to prevent the steel structure from material property reduction. However, when optimising fire protection with heat transfer simulation, repetitive modelling work and lacking recalculation principle hinder productivity improvement. This method is developed to generate steel beam models and provides an effective algorithm to optimise coating thickness considering the temperature of a specific region. The main functions of the method include:•Providing section dimensions, initial insulation thickness, target temperature and heating time, temperature allowance and mesh size as variables.•Automatically generating the Abaqus steel beam model under 3-side heating conditions.•Effective iteration algorithm to modify fire protection thickness: test containing 38 Universal beam sections with a 5 °C allowance below target shows that 55.2% were completed within five iterations and 76.3% were completed within eight iterations.

Comparative study on failure mechanism of multi-storey planar composite frames with RC beams to CFST columns subjected to compartment fire

This paper presents a theoretical study of the failure mechanism of planar composite frames composed of reinforced concrete (RC) beams to concrete-filled steel tubular (CFST) columns subjected to compartment fire. The numerical analyses on the planar composite frames with multiple stories and spans are meant to reproduce the conditions of framed members in multi-storey composite structures in real buildings. A refined finite element model is established and calibrated against the thermal and mechanical results from physical testing and shows good reliability in general. Using this model, this study proposes comparative analyses on the failure mechanisms of three typical composite frames, and discusses the effects of two significant parameters: the beam-to-column linear stiffness ratio and the fire protection thickness of the composite column. The responses of the heated composite frames, including the rotational deformation and stiffness degradation of framed joints, the internal force redistribution within framed members, and the failure mode of framed structures are investigated and discussed. The results indicate that there are two important parameters should be considered in the design of composite frames in fire.

Design and FEM modeling of a fire resistant cabinet for fusion environment

Diagnostic systems in fusion environments need to satisfy stringent requirements, often involving radiation and electromagnetic shielding as well as fire protection. A conceptual design of a multilayer cabinet for the RNC (Radial Neutron Camera) diagnostic systems, located in the equatorial port (EP) #01 in ITER, with a required fire rating REI-120 (R - integrity, E - leak tightness to hot gasses and flames, I – thermal) was analyzed from the thermal insulation (I) point of view during external fire scenario (Tmax=805 ℃ for 2 h). The modeling of the fire was based on the convective heat transfer represented by a HTC (heat transfer coefficient) of 35 W/m2K and radiative heat transfer with unit emissivity according to ISO-834. Focusing on the thermal criterion prescribed by the REI requirement, the objective was to demonstrate that the temperatures will remain below specified limits for at least 120 min subjected to given fire loads. The adopted strategy was to exploit an advanced microporous incombustible material – Microtherm® overstitched – selected for the fire insulation and being applicable for the ITER environment. A parametric 3D model was developed and solved using the Finite Element Method (FEM) and the ANSYS code, including not only the heat conduction but internal radiation via SURF252 elements and internal convection via LINK34 elements. The relation between the thickness of fire protection and the maximum temperature after 2 h of fire was analyzed for two types of designs: with internal and external fire protection. In addition to the ideal thermal connection between the layers of the cabinet, the effects of imperfect thermal contacts were analyzed by varying the thermal conductance of CONTA174 elements. The effect of the boundary conditions: adiabatic versus specified temperature was analyzed, as well as the need for protecting the supports of the cabinet. The effect of the cabinet size at constant thickness of the walls was analyzed parametrically revealing increasing temperatures for smaller cabinets – more fire insulation needed. An analytical model used to explain the size effect relate to the competing effects of increasing heat transfer area and increasing heat capacity. The developed methodology provides an easy tool for early dimensioning of the necessary fire protection layer often needed before the start of the detailed CAD design. The necessary thickness of external protection layer for the analyzed cabinet resulted in 10 mm.

Fire performance on steel-reinforced concrete-filled steel tubular columns with fire protection

Steel-reinforced concrete-filled steel tube (SRCFST) is widely used as an innovative composite structure to provide better performance in construction. This study focuses on comprehensive experimental and numerical investigations of the fire performance of SRCFST columns with fire protection under the ISO-834 standard fire test procedures. The fire resistance tests were conducted on eight SRCFST columns with various thicknesses of fire resistive coating. The fire test results, including the thermal conductivity of protection material, failure modes, temperature evolution in time, axial and lateral deformation curves, and fire resistance were reported in detail. The results demonstrated that fire protection delayed the degradation of bending stiffness and significantly increased the fire resistance. Further comparisons of fire resistance between SRCFST columns with and without fire protection indicated that the fire resistance of SRCFST column with protection thickness of 12 mm is 3.32 times higher than that of that without fire protection under an equal load level. A sequentially coupled thermal-stress finite element (FE) analysis model was develped and validated against the tested results. The measured thicknesses of fire resistive coating were compared with the predicted results to evaluate the applicatibility of the existing design method of concrete-filled steel tubular (CFST) columns to SRCFST columns with thick fire-resistive coating. The results indicated that the current design method should be adjusted or modified further to provide safe and accurate predictions of the thickness of fire protection for SRCFST columns.

Numerical analysis and structural fire design of protected SHS steel columns with thermally enhanced gypsum-based mortars

Fire protection materials should restrict the temperature increase in steel members to prevent premature steel damage and structural failure in case of fire. The design of fire protection materials must be then precise, efficient, and optimized to make steel structures more competitive in the construction sector, thus reducing the impact of one of the worst disadvantages of steel structures. Therefore, this paper presents a numerical investigation into the performance of gypsum-based mortars enhanced with silica micro and nanoparticles as passive fire protection materials to protect the steel columns against fire. Square hollow section (SHS) steel columns were considered for this investigation. Firstly, finite element models were developed and confronted with observations from experimental tests previously carried out by the authors. Secondly, a parametric study was undertaken to study the role of several parameters on the structural fire performance of such columns when exposed to the ISO 834 standard fire curve, including the fire protection thickness and type (composition), column slenderness and load level. Then numerical and analytical results from current design rules in Eurocodes were compared. And finally, changes to the steel temperature prediction method in current design standards were proposed based on the findings of this study. It was observed that the design predictions excessively underestimated the actual fire resistance of the protected SHS steel tubular columns, especially when fire protection mortars with silica micro and nanoparticles were used. The thermal properties of fire protection mortars as a function of temperature must be considered in the structural steel temperature prediction when subjected to fire conditions. It is then strongly recommended that a new revision should be done in the next generation of Eurocodes on this topic based on the proposed modifications or the presented findings.

Fire resistance of restrained circular concrete-filled double-skin steel tubular columns

In the past decade, more and more attention has been paid to the fire performance of concrete-filled double-skin steel tubular (CFDST) columns. The columns in actual structures are not isolated members and are affected by the adjacent structural members. However, little research has been conducted on the behaviour of restrained CFDST columns under fire. In this paper finite element models were developed to analyse the fire performance of axially and rotationally restrained circular CFDST columns. The predicted temperature–time curves, internal axial force–time curves and fire resistance agreed well with the related test results. Based on the verified models, a parametric study was performed to investigate the effect on the internal axial force–time curves and fire resistance. The parameters included axial load level, axial restraint ratio, diameter of the outer tube, slenderness ratio, diameter-to-thickness ratios of the outer and inner steel tubes, dimension ratio of the inner tube to the outer tube, load eccentricity, yield strengths of the outer and inner tubes, compressive strength of the concrete, fire protection thickness and rotational restraint ratio. Through regression analysis, a design formula was proposed to calculate the fire resistance of restrained circular CFDST columns.

Probabilistic risk assessment of the effects of fire service intervention on structural fire resistance design of unsprinklered buildings

This paper presents a probabilistic analysis method to explicitly include the influences of fire service intervention (FSI) in structural reliability analysis of unsprinklered buildings exposed to fire. The method considers different scenarios of fire behaviour following FSI, based on probabilistic analysis of the current UK fire data to estimate different components of intervention time, size of the fire on arrival of the fire service and extent of damage of the fire at the end of intervention. These statistical data are then used to generate random fire temperature-time curves to calculate the probability of structural failure of intumescent coating protected steel members using the Monte Carlo Simulation method. To aid deterministic design, a simplified method is developed to derive fire load modification factors (δn,FSI) to account for the effects of FSI so that when the fire load modification factor is applied, the deterministic design method gives the same probability of structural failure as that from explicit probabilistic calculation. An extensive parametric study covering a wide range of practical design factors has been carried out and an Analysis of Variance (ANOVA) is performed on the results to examine whether any design factor has significant effect on the fire load modification factor. The results show that fire growth rate and compartment floor area are the most influential. The effects of fire load, steel critical temperature and fire protection thickness have moderate effects. Based on the results of this study, it is suggested that the design fire load should not be reduced if the fire floor area does not exceed 250 m2, or the fire growth rate is ultrafast. If the fire growth rate is fast, the design fire load should not be reduced for fire floor areas less than 1000 m2. For other situations, a fire load modification factor of δn,FSI = 0.78, as in the current Eurocode, may be applied.

Fire performance of eccentrically-loaded square and rectangular tubed-reinforced-concrete columns

Tubed-reinforced-concrete (TRC) columns are gaining increasing popularity in engineering constructions, however, research on their fire performance is still limited and mainly focused on concentrically-loaded columns. In this study, extensive numerical analysis was carried out to investigate the performance of square and rectangular TRC columns under eccentric loading and exposed to ISO 834 standard fire. A sequentially-coupled thermo-mechanical finite element analysis (FEA) model was developed in ABAQUS and validated well against fire testing results. The high-temperature overall deformations, internal bending moments and cross-sectional load redistributions of square TRC columns with different load eccentricities were analysed. Parametric studies were conducted to investigate the influences of load eccentricity ratio, sectional aspect ratio, bending direction, fire protection thickness, sectional dimension, load ratio and slenderness ratio on the fire resistance of square and rectangular TRC columns. Load eccentricity was found to have a greater effect on the fire resistances of columns of lower slenderness than those of columns of higher slenderness. Rectangular TRC columns of sectional aspect ratios no larger than 2 could generally achieve identical buckling resistance as that of the equivalent square sections. The influences of sectional aspect ratio and bending direction on the column fire resistance were insignificant. A design method was then proposed for both the ambient-temperature and high-temperature designs of eccentrically-loaded square and rectangular TRC columns. The fire design method could cover both protected and unprotected TRC columns. The design method has been thoroughly validated against detailed FEA modelling and yields excellent agreements with the modelling results.

Parameters Effect on Predicting Fire Resistance of Ultra-high Strength Concrete Filled Protected Square Steel Tubular Columns

Ultra-high strength concrete (UHSC) with compressive strength greater than 100 MPa at room temperature has been developed for concrete filled square steel tubular column for use in high-rise buildings. The fire resistance of UHSC filled protected square steel tubular columns exposed to the standard ISO fire is investigated in this paper. For this purpose, numerical heat transfer analysis and nonlinear thermal stress analysis were conducted by taking into account the existing material properties, such as the thermal and mechanical properties of UHSC and high strength steel. The numerical analyses were carried out and the results were validated against the test results in terms of heat distribution and mechanical behavior. Comparison with the test results showed a reasonable agreement with finite element results in terms of temperature field prediction and load displacement behavior during the fire. Finally, based on the validated finite element model, the effects of fire protection thickness, load ratio, the strengths of concrete and steel, steel contribution ratio, and relative slenderness ratio on the fire resistance of UHSC filled square steel tubular columns were carried out and discussed.

PECULIARITIES OF EVALUATION OF METHODS OF DETERMINATION OF CHARACTERISTICS OF FIRE RESISTANCE OF BUILDING STRUCTURES

The results of the study aimed at further improvement and development of procedures for evaluating methods of determining the fire resistance characteristics of building structures are presented. The features of estimation of methods of determination of characteristics of fire resistance of building structures are determined. It is established that for the validation of experimental-calculation methods intended to determine the thickness of fire protection of building structures, which ensures their fire resistance in a wide range of parameters of these structures, it is impossible to use samples of structures with certain properties due to their inability to create. A procedure for such validation using a computational experiment method is proposed. In this procedure, accurate (conditional) temperature data for steel column specimens are determined by solving a direct one-dimensional non-stationary thermal conductivity problem. The validity of the proposed validation procedure by its application for the experimental calculation method, designed to determine the thickness of fire protection materials for load-bearing steel structures (columns and beams), has been established. It is established that the overwhelming number of calculated values of the thickness of the fire protection materials, determined by this method, exceeds its true values, which indicates the acceptability of the obtained results in terms of providing fire resistance of load-bearing steel structures. It is established that the difference between the calculated and actual values of the thickness of the fire protection materials can reach a considerable value (twice or more).The direction of further researches which are focused on revealing of influence of thermophysical properties of fire protection materials and stress-deformed state of samples of steel structures during the test on the accuracy of the method. This will identify more appropriate procedures for evaluating the method and processing the experimental data with increased accuracy.

Structural fire resistance of partially restrained, partially composite floor beams, II: Modeling

This paper is Part 2 of a two-part investigation of the structural fire resistance of a partially composite, one-way spanning steel floor beam assembly with partial translational and rotational end restraint provided by shear tab connections to a supporting frame. A preceding paper (Part 1) described a pair of experimental tests on structurally identical composite floor specimens (one protected and the other unprotected) that are subjected to fire via a large modular furnace. In this paper, those experimental results are used to validate numerical models that conservatively capture the thermo-mechanical response of the specimen assemblies to fire. Models are developed to maximize simplicity toward implementing performance-based design of these assemblies in practice. Thermal analysis of the steel is performed using a multiple lumped mass approach, which can be implemented via spreadsheet or a simple, non-iterative programmed solution. Thermal analysis of the slab via a simple one-dimensional heat flow model is compared against a more detailed computational solution. Two types of structural finite element analyses were performed: one composed of shell elements (more complex) and another composed of fiber-beam elements (simpler). The results of all models show conservative agreement with the experimental data. These models are used to analyze the tested assemblies for variations in applied load and fire protection thickness to demonstrate the utility of the ASTM E119 standard fire test as a validation baseline for performance-based structural fire engineering evaluation.

Огнезащитная эффективность гипсовых плит Knauf Fireboard для вертикальных стальных профилей различного сортамента

Цель. Установить зависимости огнезащитной эффективности – времени достижения критической температуры 500 °С при стандартном огневом воздействии – от геометрических размеров и формы поперечного сечения и толщины огнезащиты из гипсовых плит Knauf Fireboard для вертикальных двутавров и труб стальных горячекатаных.
 Методы. Использование расчетных компьютерных моделей, взаимоувязанных с результатами огневых испытаний огнезащитной эффективности гипсовых плит Knauf Fireboard для вертикальных стальных профилей различного сортамента.
 Результаты. Разработаны трехмерные расчетные компьютерные модели для моделирования теплообмена с газовой средой пожара для поперечных сечений вертикальных стальных профилей, защищенных огнестойкими гипсовыми плитами Knauf Fireboard. Установлены зависимости эффективного коэффициента теплопроводности и объемной теплоемкости огнестойких гипсовых плит Knauf Fireboard от их толщины и температуры. Установлены зависимости огнезащитной эффективности – времени достижения критической температуры 500 °С при стандартном огневом воздействии – от геометрических размеров и формы поперечного сечения и толщины огнезащиты из гипсовых плит Knauf Fireboard для вертикальных двутавров и труб стальных горячекатаных. Установлено, что время прогрева стальных профилей с огнезащитой из гипсовых плит Knauf Fireboard зависит не только от приведенной толщины металла (коэффициента сечения), но и геометрических размеров и формы поперечного сечения.
 Область применения исследований. Результаты исследований могут быть использованы для оценки огнестойкости стальных конструкций с конструктивной огнезащитой из гипсовых плит Knauf Fireboard.

Fire Fragility Functions for Steel Frame Buildings: Sensitivity Analysis and Reliability Framework

Fire fragility functions are a powerful method to characterize the probabilistic vulnerability of buildings to fire in the context of urban resilience assessment. But this method is recent and the influence of the different uncertain parameters on the functions has not been systematically studied. The first objective of this paper is to identify the prevailing parameters in constructing fire fragility functions for steel frame buildings. To this end, sensitivity analyses are conducted using Monte Carlo Simulations and a variance-based method, focusing on column failure fragilities. Fragilities for buildings with 3 to 12 stories, 0 to 3 h fire resistance rating and various occupancies are compared, assuming compartment areas ranging from 15 m2 to 80 m2. Results show that uncertainties in fire, heat transfer and structural models all generate significant variability in the fire fragility. In addition to fire load as the intensity measure, significant probabilistic parameters are the compartment geometry and openings, the thickness and thermal conductivity of fire protection, and the temperature dependent mechanical properties of steel. The second objective is to clarify the incorporation of fragility functions in a comprehensive structural fire reliability framework. A methodology for combining the functions with the ignition likelihood per year and with the fire loading in MJ/m2 is described, yielding annual probability estimates of column failure due to fire in the buildings. For a sprinklered office building designed according to prescriptive provisions, this annual probability ranges from 1.90 × 10−7 to 0.12 × 10−7 per year as a function of the building height. The probabilistic modeling techniques proposed in this paper can be used to establish consistent reliability levels in different buildings and to evaluate resilience for fire scenarios.

Fire Resistance of CFRP-strengthened Reinforced Concrete Beams under Various Load Levels

The paper presents results of ten fire resistance tests performed on reinforced concrete beams, with and without carbon fibre-reinforced polymers (CFRP) strengthening. Part of the beams have been fire protected with fire protective boards of large thicknesses. The tests were performed under various load levels, ranging from 100% to 163% of their design loadbearing capacity in fire situation prior to strengthening. Test results show that structural fire design of CFRP-strengthened elements leads to three possible calculation models of fire protection thickness needed, depending on the load level reduction.

Behavior of cellular beams protected with intumescent coatings

A new engineering practice in modern buildings is to use beams with web openings to allow the passage of services within the depth of the beam instead of underneath the beam. As the web post failure may occur before the section reaches the limiting temperature, usually an increase in the fire protection may be required for members with web openings in comparison to its equivalent solid section. The aim of this work is to present an experimental study of unloaded solid and cellular beams with circular holes in fire conditions with and without intumescent fire protection. These preliminary tests results are the basis for generating an elemental multi-temperature analysis needed to assess cellular beams with intumescent protection and give experimental results for calibration of further numerical simulations. The experimental results show that, considering the same nominal fire protection thickness, one can obtain a higher fire resistance time for solid beams when compared with cellular beams. The tests performed, with different hole diameters and web-post widths, points that to achieve the same fire resistance time, a cellular beam will need a higher fire protection compared to an equivalent solid beam. Also, a special care is needed when the intumescent coating is applied around the hole to avoid the intumescent contraction, applying for example an over coating.

Steel Columns Subjected to Thermal Gradients from Fire Loading: Experimental Evaluation

AbstractThis paper presents the behavior of axially loaded steel columns subjected to thermal gradients through their cross sections. Experimental tests were conducted on full-scale wide-flange steel columns with W8×35 and W14×53 sections made from standard grade 50 steel. The experimental investigations confirmed that variations in fire protection thickness had significant influence on the thermal gradient developing through the steel cross section. Thermal gradient along the flanges caused bowing of column specimens toward the hotter side. Thermal bowing introduced second-order moments and adversely affected stability, leading to failure of column specimens by inelastic flexural column buckling. The experimental behavior and results were compared with those obtained from detailed nonlinear finite-element analyses of the tested specimens. These nonlinear finite-element models utilized standard (temperature-dependent) material properties, and reasonably predicted the axial load-temperature-deformation beh...

Temperature Rise of a Protected Steel Column Exposed to Fire from Two Adjacent Sides

Current design equations in EN1993-1-2 for calculating the temperature rise of a protected steel column assume the uniform temperature distribution across the section in a fire, which ignore the difference in heating rate at different parts of the column. The temperature rise and the temperature distribution across the column section at a given fire exposure time were studied through finite element analysis for a column exposed to fire from two adjacent sides. Studied parameters included the section dimension and the fire protection thickness. Modification factors were proposed to the current EN1993-1-2 design equations for calculating the temperature of the un-exposed flange and the web. Differences between temperatures obtained from the modified calculation method and from the finite element simulation were less than 20°C. Temperature distributions across the two flanges and the web were assumed to be linear and methods were proposed to calculate the temperature gradient. With the increase in fire exposure time, differences between the simplified method and the finite element simulation decreased. At the fire exposure time of 120 min, differences in temperatures of the un-exposed flange and the web were less than 10%; and the differences in temperatures of the exposed flange was less the 5%.

Numerical Simulation for Predicting Fire Behavior of Axially Loaded Circular Concrete Filled Steel Tubular Columns

The present study investigates the behavior of axial loaded circular concrete filled hollow steel section (CFHSS) columns. A nonlinear finite element model using ABAQUS program was developed to investigate the fire behavior of the inspected columns from previous fire tests. The study variables include column dimensions, steel section wall thickness, concrete strength, concrete types (plain or reinforced), and fire protection thickness. The comparison indicated that the results obtained from the model were within acceptable limit of accuracy of 15%. A sensitivity study was carried out to investigate the influence of the output of the numerical model including the Poisson’s ratio of concrete, thermal conductance at the steel-concrete interface, frictional contact at steel-concrete interface, and imperfection buckling of columns. Based on the sensitivity analysis, several modelling suggestions were given in this paper which will be beneficial for further study.

Web-post buckling of fully and partially protected cellular steel beams at elevated temperatures in a fire

Web-post buckling behaviors of fully and partially protected cellular steel beams at elevated temperatures in a fire were investigated through verified finite element models. The partially protected cellular steel beam represented a protected cellular steel beam with the hole edge left unprotected. The temperature distribution in the web-post was non-uniform, even for the unprotected CSB and the fully protected CSB. The fire resistance time of a CSB increased linearly with the increase in fire coating thickness. However, for the partially protected cellular steel beam, the temperature gradient in the web-post becomes greater with the increase in the fire protection thickness. And with the increase in the fire protection thickness, the increment in the fire resistance time decreased. Additional thermal stress occurred due to the non-uniform thermal strain in the web-post. When web-post buckled, the principle compression stress in the web-post decreased suddenly. The stress at the center of the web-post could change from compression to tension due to the membrane action caused by the large buckling deformation.

Temperature distribution of steel columns protected by sprayed fire retardant coatings with three sides exposed to fire

SummaryTemperature gradient will occur when the steel framed column is heated from three sides in a fire. Current design codes provide the design equations to calculate the temperature elevation of the steel column unevenly heated in a fire. However, the design equation is based on the assumption that the temperature is uniformly distributed across the section. The temperature field of a steel column protected by sprayed fire retardant coating with three sided exposed to fire is analyzed using a verified finite element model. Parameters that affect the temperature distribution across the section are investigated, which include the section height, the web thickness, and the fire protection thickness. The coded equations based on the element factor approach are modified according to the finite element simulation results. Different temperature distribution profiles are proposed through using the heated flange temperature, the web temperature, and the protected flange temperature. Copyright © 2014 John Wiley & Sons, Ltd.