Stainless Steel Columns In Fire Research Articles

Resistance and behaviour of carbon steel and stainless steel columns with axial and rotational end‐restraints in fire

AbstractDue to the presence of neighbouring structural elements, carbon steel and stainless steel columns are typically axially and/or rotationally restrained at their ends in fire. Despite the significant influence of the axial and rotational end‐restraints on the behaviour, the fire design rules for steel columns provided in the European structural steel fire design standard EN 1993‐1‐2 were originally developed considering the structural response of axially unrestrained steel columns with pin‐ended support conditions. Thus, EN 1993‐1‐2 may provide inaccurate ultimate resistance predictions for axially and/or rotationally restrained steel and stainless steel columns in fire. Considering this, this paper investigates the behaviour and design of carbon steel and stainless steel columns with axial and/or rotational end‐restraints at elevated temperatures. A number of carbon steel and stainless steel I‐section columns are considered, taking into account different axial and rotational end‐restraint stiffnesses, room temperature loading ratios, member and cross‐section slendernesses. A new design method for the fire design of axially and/or rotationally restrained steel and stainless steel columns is put forward. The accuracy of the proposed new design method is extensively verified against the results from nonlinear shell finite element modelling.

Experimental investigation of austenitic stainless steel I-section stub columns at elevated temperatures

Due to the absence of fundamental fire test data on the cross-section behaviour of stainless steel columns, an experimental investigation of stainless steel stub columns has been conducted at elevated temperatures to fill this gap. A total of six austenitic stainless steel welded I-section stub columns were isothermally tested at three different elevated temperature levels. Two stub columns were tested at room temperature as the reference group. Complementary material tests and local geometric imperfection measurements were conducted and presented herein. On the basis of the obtained experimental results, the accuracy and reliability of the design methods of the existing European fire design standard (EN 1993-1-2) and the design method of Xing et al. for cross-sectional behaviour of stainless steel columns in fire, which has been incorporated into the upcoming version of EN 1993-1-2, are evaluated. It is concluded that, compared to the existing design rules of EN 1993-1-2, the design method of Xing et al. can provide safe and reliable cross-sectional resistance predictions for the tested austenitic stainless steel I-section stub columns.

Stainless steel I-section columns fire design considering the influence of loading history

The flexural buckling resistance of welded I-section stainless steel columns in fire considering the influence of the loading history is investigated in this paper. Finite element procedure used to replicate the response of stainless steel columns in fire has been developed and validated against existing experimental tests. Developed finite element procedure replicates real fire situation where column is firstly loaded and then heated until failure. Poor accuracy of the flexural buckling resistance according to the current Eurocode 3 design rules and recently proposed design rules was observed through an extensive parametric analysis, thus indicating that new contributing parameters need to be included in the design expressions. Two main contributing parameters were analyzed, ratio of the flange and web area Af/Aw and ratio of the flange and web thickness tf/tw. New flexural buckling rules were proposed and calibrated using the results from 3000 numerical simulations, according to the developed finite element procedure, considering a range of elevated temperature levels of practical importance, stainless steel grades, cross-sectional proportions and column slendernesses. The accuracy and reliability of new proposal were assessed against the results obtained through finite element procedure. Compared to the current Eurocode 3 design rules and recently proposed design rules, new proposal provides significantly more accurate prediction of flexural buckling resistance of stainless steel columns in fire.

Testing of stainless steel I-section columns in fire

Although there have been significant developments in the testing, simulation and design of stainless steel structural elements at room temperature, the structural response of stainless steel members in fire has received significantly less attention. In particular, full-scale fire tests on stainless steel I-section members, which are becoming increasingly widely used in structural engineering applications to meet growing load-carrying capacity demands, are currently scarce. In this paper, the results of eight full-scale anisothermal fire tests on grade 1.4301 laser-welded austenitic stainless steel I-section columns are reported. Complementary initial local and global geometric imperfection measurements, room temperature tensile coupon tests and room temperature column buckling tests are also described. On the basis of the findings from the fire experiments, the accuracy and safety of the European fire design standard EN 1993-1-2 and the recent design recommendations of Kucukler et al. [1] for stainless steel columns in fire, which will be incorporated into the upcoming version of EN 1993-1-2, are assessed. It is observed that, relative to the existing column fire design rules in EN 1993-1-2, the design method of Kucukler et al. [1] provides more reliable ultimate strength predictions for austenitic stainless steel I-section columns in fire.

Behaviour and design of stainless steel I-section columns in fire

The flexural buckling behaviour and design of stainless steel I-section columns at elevated temperatures are investigated in this paper. Finite element models able to accurately replicate the response of structural stainless steel columns in fire are created and validated. The models are then utilised to carry out extensive numerical parametric studies considering a broad range of stainless steel grades, cross-section geometries, slendernesses and elevated temperature levels. Using the results from the parametric studies, the safety and accuracy of existing design rules provided in the European structural steel fire design code EN 1993-1-2 for stainless steel columns in fire are assessed. It is observed that the existing design rules provide rather scattered and inaccurate ultimate strength predictions for stainless steel columns at elevated temperatures. For the purpose of establishing an accurate and practical means of designing stainless steel columns in fire, a new design approach, compatible with existing design rules in EN 1993-1-2, is proposed. The safety, accuracy and reliability of the proposed approach are illustrated for a wide range of cases against the results obtained through nonlinear finite element modelling. The proposed stainless steel column fire design rules are due to be incorporated into the upcoming version of the European steel fire design standard EN 1993-1-2.

Structural fire performance of axially and rotationally restrained stainless steel columns

This paper describes a step improvement in the numerical modelling of the structural response of axially and rotationally restrained stainless steel columns at elevated temperatures. The developed finite element models form a sequentially coupled thermal stress analysis that comprises a heat transfer model, a buckling analysis, and a geometrically and materially non-linear stress analysis. The proposed finite element methodology is more sophisticated than any other reported attempts to model the fire response of structural stainless steel that take into account influence of adjoining members. A high degree of predictive accuracy is achieved, with the developed models on average predicting the failure temperatures and times of test specimens reported in the literature within 2% and 6%, respectively. A parametric study is performed that investigates the influence of axial restraint stiffness, rotational restraint stiffness, column slenderness and load level. It is shown that while increasing axial restraint stiffness reduces the failure temperature of stainless steel columns in fire, increasing rotational restraint stiffness has the opposite effect. The methodology and results of this paper will provide both a tool for practice and a suite of results that can be extended to develop the existing and currently limited codified approaches to structural stainless steel design.

Experimental investigation of eccentrically compressed stainless steel columns with constraints in fire

To study the behaviour reaction and failure mechanism of stainless steel columns in fire, a series of fire tests were performed on the eccentrically compressed columns with constraints, based on S30408 stainless steel. 7 specimens were used to investigate the effects of the load ratio n, eccentricity e and axial constraint stiffness ratio β on the fire-resistance performance of eccentrically compressed stainless steel columns. The failure process and failure modes of stainless steel columns in fire were revealed. The test phenomena, heating curve, deformation curve and buckling temperature were obtained. The test results show that the load ratio n (n = 0.22–0.35), eccentricity e and axial constraint stiffness ratio β (β = 0.0458 and 0.0495) are the key factors that determine the fire-resistance performance of eccentrically compressed stainless steel columns with constraints. The larger the load ratio n, eccentricity e and axial constraint stiffness ratio β are, the lower the buckling temperature of the specimen. There are two main types of failure modes of eccentrically compressed stainless steel columns with constraints in fire: the first is the overall buckling mode and the second is the local-overall interaction buckling mode. The failure modes depend mainly on the section dimensions and the section type of the stainless steel column. The process of bearing capacity of eccentrically compressed stainless steel columns with constraints in fire goes through two stages: the prebuckling stage and the post-buckling stage. It takes times for the specimen to progress from the buckling state to the ultimate failure state. The bearing capacity of the post-buckling stage can effectively improve the fire-resistance performance of the stainless steel column with constraints.

Numerical investigation on fire resistance of stainless steel columns with square hollow section under axial compression

Based on the prior experimental studies on the 6 square hollow section stainless steel columns without axial constraints in fire, the fire resistance performance of stainless steel columns under axial compression was investigated in this paper. The numerical simulation and analysis of the performance of stainless steel columns relative to fire resistance were conducted by the finite element software ABAQUS. The effects of various parameters on the fire resistance performance of the stainless steel columns were studied, focusing on the initial defect amplitude, the load ratio and the length of the stainless steel columns. Referring to the structural fire design methods of stainless steel in the European Code (EN 1993-1-2) and the Euro Inox/SCI Design Manual, the new formulae for ultimate bearing capacity at elevated temperatures were fitted for the axially compressed stainless steel columns. The comparison of fitting results with test results and code results indicates that the fitting formulae are highly accurate and can predict the capacity and critical temperature of the axially compressed stainless steel columns in fire.

Experimental investigation on ferritic stainless steel columns in fire

This paper presents the performance of EN 1.4003 ferritic stainless steel hollow section columns when exposed to fire loading. Experimental analysis of the behaviour of ferritic stainless steel structural members in fire represents a novelty. In detail, three column tests were carried out in the framework of the Research Fund of Coal and Steel (RFCS) project named Structural Applications of Ferritic Stainless Steels (SAFSS, RFSR-CT-2010-00026). Tubular thin-walled members were considered in this study because structural applications of ferritic stainless steels generally incorporate such profiles. Three columns were tested: two square hollow sections (SHS) and a rectangular hollow section (RHS) of different length. Fire loading was applied under a constant concentrically compressive load. Identical column tests at room temperature are also reported.

Buckling of stainless steel columns and beams in fire

Material properties and their response to elevated temperatures form an essential part of structural fire design. At elevated temperatures, stainless steel displays superior material strength and stiffness retention in comparison to structural carbon steel. Although independently important, the relationship between strength and stiffness at elevated temperature also has a significant influence on the buckling response of structural components. This paper examines existing test results and presents the results of a numerical parametric study, using ABAQUS on stainless steel columns in fire. Sensitivity to local and global initial geometric imperfections, enhancement of corner strength due to cold-work and partial protection of the column ends is assessed. Parametric studies to explore the influence of variation in local cross-section slenderness, global member slenderness and load level are described. Test results are compared with the current design rules in Eurocode 3: Part 1.2, the Euro Inox/SCI Design Manual for Structural Stainless Steel and those proposed by CTICM/CSM. The results of a total of 23 column buckling fire tests, six stub column fire tests and six fire tests on beams have been analysed. Overly conservative results and inconsistencies in the treatment of buckling phenomena and the choice of deformation limits are highlighted. A revised buckling curve for stainless steel in fire, consistent strain limits and a new approach to cross-section classification and the treatment of local buckling are proposed. These revisions have led to a more efficient and consistent treatment of buckling of stainless steel columns and beams in fire. Improvements of 6% for column buckling resistance, 28% for stub column (cross-section) resistance and 14% for in-plane bending resistance over the current Eurocode methods are achieved.

Temperature development in structural stainless steel sections exposed to fire

The initial material cost of structural stainless steel is about four times that of structural carbon steel, due largely to the expense of the alloying elements and the relatively low volume of production. Given broadly similar structural performance, additional areas of benefit need to be identified and exploited in order to establish stainless steel as a viable alternative material for construction. In addition to the familiar benefits of corrosion resistance, low maintenance, high residual value and aesthetics, one such area is fire resistance. The mechanical and thermal properties of stainless steel differ from those of carbon steel due to variation in chemical composition between the materials. A comparison of these properties for austenitic stainless steel with those for structural carbon steel is presented herein, and implications of the differences explored. Accurate and efficient determination of the temperature development within a structural member upon subjection to fire is paramount. In this paper, comparisons of temperature development in structural stainless steel sections are made between existing test results, numerical simulations and the simple calculation model of Eurocode 3: Part 1.2. Based on these comparisons, revised values for the heat transfer coefficient and emissivity of structural stainless steel members exposed to fire are proposed. In the temperature development calculation model of EN 1993-1-2, it is proposed that emissivity be taken as 0.2 (in place of the currently adopted value of 0.4) and the heat transfer coefficient be taken as 35 W/m 2 K (in place of the currently adopted value of 25 W/m 2 K). The significance of such revisions to the fire resistance and critical temperature is assessed. Application of the revised values in the predictive models for member resistances at elevated temperatures in Eurocode 3: Part 1.2 also reveals improved agreement with test results on axially loaded stainless steel columns in fire, and average enhancements in fire resistance of 10%.