Buckling analysis of partially protected cold-formed steel channel-section columns at elevated temperatures (original) (raw)
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Buckling analysis of cold-formed steel channel-section beams at elevated temperatures
Journal of Constructional Steel Research, 2015
This paper presents a numerical investigation on the buckling behaviour of plasterboard protected CFS channelsection beams subjected to uniformly distributed loads when exposed to fire on its one side. The work involves three phases, namely heat transfer analysis, pre-buckling analysis and buckling analysis. The heat transfer analysis is accomplished using two-dimensional finite element analysis methods, from which the temperature fields of the channel-section beams are obtained. The pre-buckling analysis is completed using the Bernoulli bending theory of beams with considering the effects of temperature on strain and mechanical properties. The buckling analysis is performed using combined finite strip analysis and classical Fourier series solutions, in which the mechanical properties are considered to be temperature dependent. The results show that there are significant temperature variations in web, fire exposed flange and lip. Also, it is found that the buckling behaviour of the beam with temperature variation in its section is quite different from that of the beam with a constant uniform temperature in its section.
Columns under natural fire conditions are usually exposed to a non-uniform temperature distribution in the longitudinal direction. The motivation for this study stems from zone modeling of a compartment fire where the gas layers are artificially divided into two zones, namely the hotter upper zone and the cooler lower zone. However, for field modeling of a compartment fire, more detailed information of the temperature distribution can be obtained. Depending on the required accuracy, two different idealizations of temperature distributions are analyzed in this paper, namely linear distribution from zone modeling and piece-wise step distribution from field modeling in the longitudinal direction. Compared to a column with uniform temperature distribution, both of them represent more realistically the thermal response of a column, which experiences greater temperature with increasing height. The difference in temperature between the top and bottom ends of a column can be quite significant, particularly prior to the flashover condition. Advantage can be made of this in a performance-based approach to ascertain the stability of a column subjected to a prescribed fire size. In this paper, the stability of a pin-ended steel column under a non-uniform temperature distribution is studied. Although the formulations are based on linear elastic assumptions, the paper explores the validity aspect of the approach and shows that it can be applied to columns with a minimum slenderness ratio where plasticity is negligible. Across a section, the temperature is assumed to be uniform. Two linear elastic springs connected to the column ends simulate the axial restraints from the adjoining unheated structure. The objective is to derive closed-form solutions to enable engineers to quickly ascertain the column stability under a non-uniform temperature distribution, without recourse to finite element modeling.
Buckling of an Axially Restrained Steel Column Under Fire Loading
International Journal of Structural Stability and Dynamics, 2011
Analytical procedure, based on the linearized stability analysis, is presented for the determination of the buckling load and the buckling temperature of a straight, geometrically perfect, axially loaded steel column subjected to an increasing temperature simulating¯re conditions. The nonlinear kinematical equations and the nonlinearity of material are considered. The stressÀstrain relation for steel at the elevated temperature and the rules for reduction of material parameters due to increased temperature are taken from European standard EC 3. Theoretical¯ndings are applied in the parametric analysis of a series of Euler's columns subjected to two parametric¯res. It is found how the slenderness of the column, the material nonlinearity, the temperature dependence of material parameters, and the sti®ness of restraints at supports e®ect the critical temperature. While these parameters have major in°uence on the critical temperature, they have no e®ect on the shape of the buckling mode. ¯re is regulated by several building codes such as, for example, Eurocode 3 1 , BS5950 2 , and ISO 834 3 . These standards o®er simpli¯ed methods of analysis for isolated columns, which sometimes do not give su±ciently reliable quantitative predictions of the¯re-bearing capacity of a column, if it is a part of a frame.
The Buckling and Post-Buckling of Steel C-Columns in Elevated Temperature
Materials, 2019
This work deals with the investigation of a steel thin-walled C-column subjected to compression due to temperature increase. These experimental studies of the compressed columns in post-buckling state were conducted to determine their load-carrying capacity. To ensure appropriate supports and keeping of columns, plates with grooves were constructed. The tests of the columns’ compression for different preloads were carried out. By comparing the experiment results, numerical calculations based on the finite element method (FEM) and the semi-analytical method (SAM) of solution were performed. The computations were executed with the use of full material characteristics with consideration of large strains and deflections. Furthermore, while observing the deformation of columns, a non-contact Digital Correlation ARAMIS® system was employed whose calculated results of deformations are very close to the results of the numerical method. The paper revealed that maximum recorded loads under te...
Parametric Study on the Fire Resistance of Steel Columns with Cold-Formed Lipped Channel Sections
Applications of Structural Fire Engineering, 2016
Steel structural elements with cold-formed thin-walled sections are becoming increasingly common in buildings due to their lightness and ability to support large spans. In these members, local, distortional and global instabilities are important common failure modes. At high temperatures, these instability phenomena are intensified. This paper presents a numerical study on the behaviour of columns with cold-formed C-sections in case of fire when subjected to compression. A parametric study, considering different steel grades, temperatures and different cross-sections with different slendernesses, is presented. Comparisons are also made between the numerical results and analytical design rules, such as the EN1993-1-2, using its Annex E or its French National Annex, where a different constitutive law is recommended for cold-formed profiles. It is possible to conclude that the simple calculation rules are on the safe side but sometimes too conservative.
Periodica Polytechnica-civil Engineering, 2021
In this paper, a numerical investigation on the global buckling capacity of the axially compressed steel columns with hot-rolled I crosssection at elevated temperatures is presented. Geometrically and materially non-linear finite element model and the ABAQUS software were used to determine the buckling resistance. The numerical ABAQUS model was validated using experimental results available in the literature, and then the validated numerical model was used to generate a database of load-carrying capacity. The parametric study covered three different cross-section classes (class 1, 2 and 3), ten different non-dimensional slenderness ̄λ = 0.5, 0.6, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2.0), three different temperatures (400°C, 500°C, 600°C), and two stress-strain constitutive relations including (the nonlinear material model adopted in the European guidance for structural fire design EN1993-1-2, and a Bilinear material model), with and without residual stress. The influence of the model...
Buckling Modes of Cold-Formed Steel Columns
International Journal of Engineering and Technology, 2013
The goals of this study are to understand different buckling modes, determine the buckling mode and maximum buckling capacity of the built-up C-channels, and evaluate the AISI-2001 Specification. For these goals, the following was conducted: 1) different buckling modes of cold-formed steel columns were investigated; 2) previous research on built-up columns and testing rigs for column buckling was reviewed; and 3) the authors' buckling test results of 42 cold-formed built-up columns were examined. The study and review help better understanding of the buckling modes and the effect of design or testing parameters on the buckling behavior. The results show inconsistencies in the calculated values by AISI-2001 as compared to the maximum capacity loads determined from the buckling tests. The orientation of the member substantially impacts the maximum load of the member.
The paper presents the investigation on cold formed steel lipped channel columns experiencing distortional and global buckling interaction under axial compression. Five cross sections are chosen based upon the limitations given in the draft IS 801 code. The cross section dimensions and length ensures equal distortional/global critical buckling loads, thus maximizing the distortional/global mode interaction effects through elastic buckling analysis using CUFSM software. The plate slenderness ratio (b/t) is within the limit to avoid local buckling. The ends of the columns are considered as Pinned-Pinned. The Numerical analysis are carried out by the finite element package ANSYS. Finite element model include the geometric and material non-linearities. Geometric imperfections are incorporated in the model by extracting distortional and global modes obtained from buckling analysis. Parametric studies are carried out by varying the yield stress as 250,350 and 550 N/mm2.Theoretical Analysis are carried out by Direct Strength Method DSM-AISI 100-2007 and Australian Standard AS/NZS:4600-2005.The results are compared and the effect of distortional and global interaction on ultimate strength is discussed.
Alternative approach to buckling of square hollow section steel columns in fire
Journal of Constructional Steel Research, 2014
Stability of axially loaded steel columns with square hollow sections at elevated temperatures is studied herein. At present the Eurocode model for checking buckling capacity of columns in fire has been developed on the similar basis as for ambient conditions. It is shown that due to the effect of complex non-linear behavior the standard design model is not always adequate and in certain situations prediction of buckling capacity of columns according to the common design formulas may even reach results on the unsafe side. The main focus of this work is the performance of an analytical model against advanced numerical methods. For this purpose extensive numerical study was performed using non-linear FE method. Based on the results obtained with advanced calculation models of column behavior at elevated temperatures an analytical model has been proposed and verified. The proposed model accounts for variable non-linear stiffness properties, which have significant effect on the buckling capacity of axially loaded columns in fire. The advantage of the method is the format, which is convenient for incorporation into common design algorithms.
Effect of Boundary Conditions on the Creep Buckling of Steel Columns in Fire
2016
This paper presents highlights of a preliminary computational study conducted using Abaqus to investigate the influence of boundary conditions on the creep buckling behavior of steel columns at elevated temperatures due to fire. W12×120 wide flange columns with the unsupported length of 240 inches are used in the simulations. Thermal creep of steel is modeled following equations proposed by Fields and Fields for the creep of ASTM A36 steel. Four different classical support conditions and seven imperfection amplitudes are considered to quantify the effect of boundary conditions on the time-dependent strength of steel columns in fire. Thermal restraints, both axial and rotational, were ignored in the analyses. Representative results from creep buckling tests simulated at 500 °C are presented and discussed. Results from creep buckling simulations presented in this paper indicate that the rotational and translational restraint at the column ends along with the initial crookedness of the...