Fire Resistance Of Steel Columns Research Articles

Fire Resistance Performance of Constrained H-Shaped Steel Columns with Uneven Vertical Temperature Distributions

Steel columns, which are widely used in building frameworks and spatial structures, are susceptible to capacity degradation during fires, potentially leading to the overall collapse of buildings. Existing research on the fire resistance of steel columns assumes that the temperature loads encountered by steel columns are evenly distributed vertically. However, real-world fire scenarios often feature significant vertical temperature differences. Therefore, this study comprehensively investigated these variations to derive a temperature curve that accurately represents real fire conditions. Subsequently, the fire resistance limits of steel columns were studied using this temperature curve, leading to a revised calculation formula for the critical fire resistance temperatures of steel columns. The following conclusions were drawn: (1) Nonuniform longitudinal temperature distributions are influenced by parameters such as the fire source distance, the heights of ventilation openings, and the distance between a vent and the temperature measurement point. Among them, the fire source distance has the greatest impact, with the maximum longitudinal temperature difference reaching over 500 °C. (2) Variations in the load ratio and longitudinal temperature differences alter the failure positions of steel columns, reducing their critical temperatures by up to 200 °C. (3) The revised critical fire resistance temperature formula is more accurate and safer compared with that outlined in the “Technical Code for Fire Protection of Steel Structures” (GB51249-2017). These findings offer valuable insights for the fire designs of steel columns.

Experimental study on fire resistance of high strength Q960 steel columns under axial compression

In order to obtain the mechanical behavior of H-shaped high-strength Q960 steel column under axial compression in fire, the bearing capacity tests of two Q960 steel columns at ambient temperature and fire resistance tests of six Q960 steel columns at elevated temperature were carried out. By considering different slenderness ratios, load ratios, and heating rates of the test columns, the furnace temperature, column temperature, lateral displacement, and axial displacement were measured and recorded. Then, critical temperature, fire resistance, and failure mode of the columns were obtained. The thermal-mechanical coupling analysis model for the Q960 steel column was established by using ABAQUS finite element analysis software. After verifying the accuracy of the model, parameter analysis was carried out to investigate the effects of load ratio, slenderness ratio, geometric imperfection, thermal creep, residual stress, and steel strength on the fire resistance of steel columns. Based on the test data and analysis results, a fire resistance design method for high-strength Q960 steel columns under axial compression is proposed.

The effect of thermal creep on the fire resistance of steel columns

An appropriate assessment of the structural fire resistance of steel columns necessitates an accurate mechanical material modeling considering thermal creep in the stress-strain response of steel at elevated temperatures. This paper presents a novel thermal creep model achieved from available experimental results in the literature and its application to structural members in fire within a numerical study on the proposed creep model. Based on this model, a comparative set of numerical studies is performed for a specific benchmark structure in fire conditions, considering protected and unprotected structural steel columns, different stress ratios, different severity of fire exposure and the role of creep buckling. The effect of thickness of the protection material and associated heating rate of the structure on the fire resistance with regard to creep buckling is also investigated. In addition, the structural buckling behavior in fire conditions with explicit consideration of thermal creep in the aforementioned model is studied in comparison to the existent simplified constitutive material model with implicit creep consideration in EN 1993-1-2 [1] for the benchmark structure. The results of this paper highlight the necessity of including thermal creep in the state-of-the-art advanced structural fire design in engineering practice.

EVALUATION OF FIRE RESISTANCE OF FIRE PROTECTED STEEL STRUCTURES BY CALCULATION AND EXPERIMENTAL METHOD

Based on the developed geometric, physical, computer and finite element model, the fire resistance of fire-resistant steel structures was evaluated by calculation and experimental method. The adequacy of the developed computational-experimental method for assessing the fire resistance of fire-resistant steel structures in assessing the fire resistance of a fire-resistant I-beam steel column was verified. The results of tests for fire resistance of steel columns with fire-retardant coating at standard temperature of the fire without the load applied to them (temperature in the furnace, temperature in certain places on the surface of fire-retardant steel columns, the behavior of the investigated fire-retardant coating). The analysis of tests on fire resistance of fire-resistant steel columns exposed to fire at standard temperature (temperature in the furnace, temperature in places of measurement of temperature on a surface of columns, behavior of a fire-retardant covering) is carried out. A computer model of the «steel column – reactive flame retardant coating» system has been built for numerical simulation of non-stationary heating of such a system. Simulation of non-stationary heating of the system «steel column – fire-retardant coating» in the software package FRIEND with the specified parameters (geometric model, thermal effects, initial and boundary conditions, properties of system materials). The reliability of the results of numerical modeling with real experimental data on the duration of fire exposure at the standard temperature of the fire to reach the critical temperature of steel. Based on the comparison of experimental results and numerical simulations, a conclusion is made about the adequacy of the developed model to the real processes that occur when heating fire-retardant steel columns without applying a load under fire conditions at standard fire temperature. The efficiency of the proposed calculation and experimental method for assessing the fire resistance of fire-resistant steel structures has been confirmed.

FE Model Validation and Advanced Analyses of Steel Members with Steel Claddings at Elevated Temperatures

AbstractIn order to investigate the stabilization effect of distinct steel members by steel cladding system including trapezoidal sheeting and sandwich panels in fire using advanced analysis techniques, the computer models and modeling techniques must be validated by available experiment tests. However, the fire tests in this area are scarce. As part of a wider validation scheme, this paper presents the modeling method using Ls Dyna explicit solver and the comparison of FE analysis results with four experimental tests at elevated low to medium temperatures (150‐300 °C) in RFCS STABFI project. After the model validation, the advanced fire analyses of steel columns with two types of steel claddings such as trapezoidal sheeting and sandwich panel are carried out to investigate the stabilization effect. The analyses show that for the studied I‐section column under both axial compression and bending moment, the position of steel claddings, either connecting with the tension flange or the compression flange, has significant influence on the fire resistance of the steel columns. When the trapezoidal sheet is connected with the compression flange, the fire resistance of steel column is 17 % more than that without cladding. Sandwich panel cladding has influences on the deformational behavior of column during the fire exposure. However, the contribution of sandwich panels to the fire resistance of steel columns is negligible due to the delamination of inner panel sheet.

An experimental study on crack and debonding of intumescent coatings and their effects on temperature development of steel elements

This paper presents the results of an experimental study to investigate failure modes of intumescent coatings and their effects on temperatures attained in steel sections and fire resistance of steel columns. Tests were carried out on unloaded steel plates, unloaded short sections and axially loaded long columns. The loaded column specimens had four different surfaces, stainless steel, untreated carbon steel, sand-blasted carbon steel and carbon steel with one layer of fibre cloth. The failure modes of intumescent coating char included cracks, debonding and detachment. Detachment seemed to have occurred after the fire tests because there was no evidence of a sudden jump in temperature. The cracks varied from fine distributed cracks to large discrete cracks. These intumescent coating failure modes affected not only average temperatures of the steel but also temperature distributions in the steel sections. The average temperatures attained in the unloaded steel sections were lower than those in the loaded steel columns. The temperature differences for the unloaded plate and sections were relatively small, lower than 2.2% and 6.3% respectively, while they were high for the loaded test specimens, 10–20% of the average.

Creep effect on critical strength of high-strength steel columns exposed to fire

Under fire conditions, the fire resistance of steel columns may be critically affected by steel creep. However, in the current codes of practice, creep effect has not been explicitly considered in determination of the high-temperature load-bearing capacity of steel columns. This may result in unsafe predictions of the load-bearing capacity of steel columns exposed to fire. In this study, both numerical and theoretical approaches are employed to study the creep effect on the critical strength of Chinese grades Q550, Q690, and Q890 high-strength steel columns. First, the creep buckling behavior of steel columns is numerically studied using the finite element program ABAQUS, and then validated against the existing experimental results. The creep buckling load factor, which is the ratio of the buckling load with creep effect to that without creep effect, is calibrated from the numerical approach and plotted against creep buckling time. The creep buckling load factor vs. buckling time curves are also established from the theoretical approach and compared with the curves established from tests and numerical analyses. A parametric study is then conducted by using a validated theoretical approach to investigate the effects of several variables including slenderness ratio, temperature, and material strength on the creep buckling load of high-strength steel columns. Based on the parametric study results together with current code of practice EN 1993-1-2, the modification factors of the buckling load with creep effect are proposed. The results demonstrate that under fire conditions without considering the creep effect, the buckling load of high-strength steel columns may be overestimated.

일반 구조용 압연강재와 용접 구조용 압연강재로 제작된 H형강 기둥부재의 해석적 내화성능 평가

Fire resistance is an important factor in sustaining the structural stability of steel framed buildings on fire. However, evaluation of the fire resistance of steel columns has been conducted using rolled steels for general structures, SS 400. Recently, rolled steels for welded structures, such as SM 400 and SM 490, have been used frequently because they have better performance of welding than the SS 400. However, there has been doubt about how much fire resistance SM 400 and SM 490 have. To evaluate by calculation the fire resistance of an H-section column made of SS 400 its mechanical and thermal properties were derived and suggested respectively in the form of regressive equations and the analysis was done based on heat transfer and thermal stress analysis. In this study, the results of the evaluation of H-section columns made of SS 400 with loaded fire tests turned out to be conservative. As a result, a new guideline is required to get the exact fire resistance of another structural steel. †(Received June 27, 2013)

Experimental study on the fire resistance of steel columns protected with fire boards

The thickness of the fire protection material of steel columns should be determined to guarantee the load-bearing capacity of the steel columns during a fire. In Korean standards, the strength capacity of steel columns is evaluated by measuring the axial deflection or surface temperature of only one H-section of 300x300x10x15 or similar dimensions in a fire test. Once the thickness of a fire protection material is approved, it can be applied to any section, regardless of the size and shape. However, in order to properly protect a building from a severe fire, the appropriate thickness of the fire protection material should be determined with consideration of the section factor, size and shape of steel columns in accordance with building regulations. This paper describes a series of full-scale and small-scale fire tests which were conducted on H-section and Rectangular Hollow Section (RHS) steel columns protected with glass fiber reinforced gypsum (GRG) boards and cellulose fiber reinforced cement (CRC) boards. The main factors of the fire tests were the section factor, the section shape and the thickness of the fire protection materials. Simple equations to predict the thickness of a fire protection material of steel sections, accounting for the shape factor and the required fire resistance, are proposed. A comparative study on the efficiency between the newly developed columns with two types of fire boards and the conventional columns with a combination of spray and gypsum boards was also conducted, and results are reported herein.

Damage evaluation of the steel tubular column subjected to explosion and post-explosion fire condition

Fires following explosion are considered one of the most serious secondary disasters in the blast events, which are frequently occurring in the terrorist attacks and other blast accidents. In the recent decades, a significant amount of research work has been carried out to study the structural response under blast loads, and it is found that due to the superior mechanical properties of steel material, steel structures are adequate to withstand a medium-scaled blast loading. However, since the strength of steel is sensitive to temperature, the post-explosion fire action should be involved in the evaluation of structural damage in the blast events. This paper is devoted to introduce a numerical method for predicting the integrative damage of steel tubular column subjected to blast load and the following fire action. The damage caused by blast load would significantly reduce the fire resistance of steel column, which includes two aspects: mechanical damage and geometrical damage. In order to describe the mechanical damage under the blast loading, a damage scalar is defined in the constitutive model, and it is used to represent the reduction of material strength. The geometrical deformation induced by blast load is treated as the initial condition in the fire analysis. Pressure–Impulse diagram is employed to describe the damage of the steel tubular column under blast loading. In the second step, fire analysis for the explosion-survived column is carried out. Obviously, the residual vertical capacity of steel column is related with the fire exposure time. In order to clarify the interaction between the explosion and the post-explosion fire action, a more inclusive function, characterized by three variables: pressure, impulse and fire exposure time, is presented in this paper, and it can be used to predict the residual capacity of the steel column subjected to blast load and exposed to fire for a specific time. In the last section, parametric studies are conducted to observe the effects of geometric size on the failure evolution of steel columns. The main objective of this research work is to provide guidance for assessing damage level of the steel tubular columns that have survived blast loading and expose to the following fire condition.

Fire resistance of steel columns with restrained thermal elongation

The behavior of steel columns subjected to fire depends on their interaction with the surrounding building structure. To improve knowledge of the phenomenon a great many fire resistance tests have been carried out on steel columns with restrained thermal elongation. A new experimental system was designed and constructed to carry out the tests.The columns tested had slenderness of 50.6 and 63.3, an initial applied load of 30% and 70% of the column's design value of the buckling load at room temperature and an axial stiffness of the surrounding structure of 13, 45 and 63.3kN/mm. Also tested were columns with initial applied loading eccentricity equal to the width of the cross-section in the direction of the weak inertia axis or both principal inertia axes.The results showed that increasing the stiffness of the surrounding structure may not lead to a reduction of the column's critical temperature. This is because, associated with an increase of the axial stiffness is an increase of the rotational stiffness, which has an opposite effect to the first one. It was also noted that the higher initial applied load levels resulted in shorter critical temperatures of the columns.

Experimental study on performance of elliptical section steel columns, under hydrocarbon fire

Elliptical structural steel hollow sections represent a recent addition to the range of steel sections available to structural engineers. However, despite the extensive interest in their use on the basis of both architectural attraction and structural efficiency, a complete absence of fire resistance design guidance is restraining applications. This paper presents the first study ever conducted to investigate the fire resistance of steel columns with Elliptical Hollow Sections (EHS). Six columns of two slenderness λ = 40.1 and λ = 50.8 were tested under three loading levels ( α L = 0.3 , 0.45 and 0.6) and subjected to a hydrocarbon fire curve. The paper provides the recorded data of axial displacements and temperature profiles of the EHS steel columns, while highlighting the unique local and overall buckling failure modes of the Elliptical Hollow Section.

Behavior of steel columns in a fire with partial damage to fire protection

Abstract An experimental study is performed on two specimens in a furnace to investigate the fire behaviour of steel columns with partial loss of fire protection. The steel columns are connected by flush end-plates at two ends and the axial load is kept constant with a load ratio of 0.55 subjected to an elevation of temperature. The specimens are protected with 20 mm thickness of fire protection. The damaged length of fire protection is 7% of the complete length of the column for specimen S-1 and 14% for S-2 at the two ends of the steel columns. The temperature of atmosphere around the specimens in the furnace is assumed to follow the ISO834 standard temperature and the temperatures and displacements are measured in the experiment. The temperature distribution along the steel column is modelled by finite element analysis and compared with the measured results. A continuum model is presented to predict the ultimate load capacity or critical temperature of the columns with fire protection damage. Analyses are carried out on the specimens and compared with the experiment. Experimental and analytical results showed that the fire resistance of steel columns with partial damage to the fire protection is reduced. The damage length of the fire protection has a great effect on the fire resistance of steel columns. The failure of the specimens mainly resulted from the buckling or yielding at the portion where the fire protection is damaged.

Extended Rankine approach for bi-axially loaded steel columns under natural fire

Up till now, there has been limited research work conducted on bi-axially loaded steel columns under fire conditions. Under normal ambient temperature, the load-bearing capacity of steel columns is governed by the interaction of strength and stability considerations, which gives rise to the Rankine method. The authors extended this method to predict the fire resistance of steel columns subjected to bi-axial loading under standard fire curve. Basically, the authors developed an interaction equation based on failure surface to account for the effects of axial load and bending moments in two directions. Predictions from the proposed approach were benchmarked against a well-established finite element program SAFIR for steel columns under standard fire conditions. The same approach is then extended to include natural fire curves. To model a compartment fire with different geometries, thermal characteristics of boundary walls, different fire loads and ventilation factors, a zone fire modelling program Ozone was used. Coupling Ozone to SAFIR, the failure times of steel columns in a compartment fire were predicted. These numerical predictions were compared with those from the proposed approach and reasonable agreement was obtained.

Heating rate and boundary restraint effects on fire resistance of steel columns with creep

This paper presents a series of numerical studies conducted on thermally restrained steel columns subjected to predominantly axial loads. The parameters under investigation include the column slenderness ratio λ , axial restraint ratio β l , rotational restraint ratio β R , and axial load utilisation factor μ N . For the heating scheme, only the cross-sectional uniform heating profile is investigated, as columns are normally exposed to fire on four faces. A finite element program FEMFAN2D is applied for the analyses and creep strain has been explicitly considered. The behaviour of thermally restrained steel columns is explained in terms of the development of cross-sectional stresses and strains. Extensive investigations are conducted to study the creep effect on the development of stress and strain, internal forces and critical temperature of a column. It shows that for some considered cases, the creep effect becomes significant for as low as 350 ∘C. Besides, the study also shows that the rotational restraints significantly reduce the column effective length under fire conditions and increase the column critical temperature through restoring moment. It is suggested that the effective length ratio for non-sway generally restrained columns can take the value of 0.55 for design purposes.

An Investigation of the Reduction in Fire Resistance of Steel Columns Caused by Loss of Spray-Applied Fire Protection

The effect of the loss of fire protection material on the fire resistance of steel columns is examined. A three-dimensional finite element heat transfer analysis is conducted to simulate the ASTM E119 fire resistance test. The predicted temperature distributions within the member over time are used in conjunction with the thermal endpoint criteria specified in ASTM E119 to provide an estimate of the fire resistance of the member. Several variables are then examined with respect to their effect on the fire resistance of a member. For a given exposure, the area of the missing protection and the size of the column are found to have an appreciable effect upon the fire resistance of the column regardless of the protection thickness. The area of the missing protection seems to be the primary factor in the temperature rise and fire resistance assessment of the column. The temperature rise in the column is primarily sensitive to the amount of missing protection, with the size of the column gaining significance only later in the test.

Fire resistance of steel columns with elastically restrained axial elongation and bending

Structures impose elastic restraint to the axial elongation of steel columns submitted to fire and also to the rotation of their extremities. A computer program, based on the Finite Element Method, is used to analyse the influence of these two kinds of elastic restraint on the critical temperature of columns. The values of the load eccentricity, the column slenderness, and the axial and rotational restraint imposed by the structure were chosen as to cover the great majority of situations to be found in practice. It is shown that axial restraint diminishes, in general, the critical temperature of steel columns, while rotational restraint increases it. The fire design situation, proposed in ENV 1993-1-2, of column with fixed ends and no axial restraint, is acceptable only for less slender columns and in the cases where the frame provides sufficiently high rotational restraint to the ends of the column. When the axial restraint is high and the rotational restraint is low, the real critical temperature of steel columns can be much lower than the critical temperature calculated according to the simplifications proposed in ENV 1993-1-2.

The effect of axial restraint on the fire resistance of steel columns

The paper represents the outcomes of a joint research between the University of Ulster and the University of Sheffield into the performance of axially restrained steel columns during fire. The Ulster experimental program incorporates 37 high temperature tests that investigate three parameters: slenderness ratio (λ=49,75,98), degree of axial restraint (αk=0, 0.1,0.2,0.3) and loading ratio (αL=0,0.2,0.4,0.6). A unique test rig which allows the application of both axial restraint and loads, either separately or at the same time has been especially designed for the experimental program. Typical results from the fire tests are presented, which illustrates characteristic response of the columns to the imposition of axial restraint, coupled with the temperature increase. In addition, trend graphs charting generic response are discussed. An associated computational study by Sheffield provides satisfactory accurate computer simulations of fire tests, using standard materiel property input data. The computer modelling exercises has been extended to parametric studies, to include the effects of many more levels of axial restrain. The linked experimental and computational study has thus validated a computational model, which can be used to provide the basis design guidance of the behaviour of restrained columns in fire situations.

Fire Resistance of Steel Columns Filled with Bar-Reinforced Concrete

Parametric studies, using mathematical models, were carried out to determine the influence of various factors on the fire resistance of steel hollow structural section (HSS) columns filled with bar-reinforced concrete. Data from the parametric studies were used to develop simple expressions for calculating the fire resistance of bar-reinforced concrete-filled HSS columns with circular and square cross sections. The validity of the calculation procedure was established by comparing the calculated fire resistances with those obtained from fire tests on columns. The procedure, which is suitable for incorporation in design codes, provides a rational and easy-to-use design method for evaluating the fire resistance of hollow steel columns filled with bar-reinforced concrete for any value of the significant parameters that determine it, such as load, cross-sectional dimensions, effective length, and concrete strength.

The critical temperature of steel columns with restrained thermal elongation

The influence of restraint of their thermal elongation on the fire resistance of steel columns is studied. The restraining forces are calculated as a function of steel temperature. The influence of several parameters on the fire resistance is analyzed: stiffness of the structure to which the column belongs; slenderness of the column; and eccentricity of the restraining forces.