Steel Compression Members Research Articles

Thin-Walled Cold-Formed Compressed Steel Members and the Problem of Initial Imperfections

The paper deals with the influence of initial imperfections caused by the production process and presents fundamental information about experimental and theoretic-numerical research to determine the load-carrying capacity of thin-walled cold-formed compressed steel members. The investigated members have closed cross-sections made from a homogeneous material. The theoretic-numerical analysis in this paper is oriented towards investigating and modelling initial imperfections effects on the load-carrying capacities of the mentioned members, while the experimental investigation verifies the theoretical results and investigates the behaviour of the members during the loading process.

Evaluation of compression member buckling and post-buckling behavior using artificial neural network

Various methods can be used to investigate buckling phenomena in a steel compression member. Among these methods, experimental formulas, semi-empirical formulas, closed-form solutions and classic methods based on differential equations as well as numerical methods based on finite elements are most commonly used. All of these methods have associated complexities. Thus, it is very difficult to perform a comprehensive parametric study on the buckling phenomenon of a compression member using these methods. The simplicity of the mathematical concepts used in ANNs (artificial neural networks) and their ability to model complex problems have led to the popularity of ANNs. After the learning step of an ANN, a function can be determined as a relationship between the input variables and output parameters, which is a load–displacement relationship in this article. It is then possible to perform an extensive parametric study on the buckling behavior of a compression member. In this research, the network can also extract the critical load–slenderness relationship. Using this network, it is possible to conduct an accurate study on the effects of various parameters at the critical load as well as to evaluate the sensitivity of the critical load to each variable used in the ANN training.

Experimental Study on Interactive Buckling Behavior of Steel Compression Members with Thin-Walled Stiffened Box Cross Section

Experimental Study on Interactive Buckling Behavior of Steel Compression Members with Thin-Walled Stiffened Box Cross Section

Experimental - theoretical study of axially compressed cold formed steel profiles

Analysis of axially compressed steel members made of cold formed profiles presented in this paper was conducted through both experimental and numerical methods. Numerical analysis was conducted by means of "PAK" finite element software designed for nonlinear static and dynamic analysis of structures. Results of numerical analysis included ultimate bearing capacity with corresponding middle section force-deflection graphs and buckling curves. Extensive experimental investigation were also concentrated on determination of bearing capacity and buckling curves. Experiments were conducted on five series with six specimens each for slenderness values of 50, 70, 90, 110 and 120. Compressed simply supported members were analyzed on Amsler Spherical pin support with unique electronical equipment and software. Besides determination of forcedeflection curves, strains were measured in 18 or 12 cross sections along the height of the members. Analysis included comparisons with results obtained by different authors in this field recently published in international journals. Special attention was dedicated to experiments conducted on high strength and stainless steel members.

Experimental Study on Buckling Strength of Angle Steel Compression Members with Built-up Bracing

Experimental Study on Buckling Strength of Angle Steel Compression Members with Built-up Bracing

Plastic mechanisms database for thin-walled cold-formed steel members in compression and bending

Short members of thin-walled cold-formed (TWCF) steel sections, in compression and bending, fail by forming local plastic mechanisms. Taking into account the localised buckling pattern, the collapse of slender members, due to the interaction between local and overall buckling modes, is always characterised by local plastic mechanism failure mode. Based on these two observations, the ultimate strength in interactive buckling of these members can be regarded as an interaction between localised plastic mode and overall elastic one.The yield line mechanism method has been widely used to predict the sectional strength (e.g. local) of thin-walled cold-formed steel members that involve failure mode characterized by local collapse mechanisms. This method can be also used to study post-collapse behaviour and to evaluate the load-carrying capacity, ductility and energy absorption.This paper is based on previous studies and some latest investigations of authors, as well as the literature collected data. It represents an attempt to make an inventory, classify and range geometrical and analytical models for the local-plastic mechanisms aiming to characterize the ultimate capacity of some of the most used cold-formed steel sections in structural applications.

Numerical modelling of light gauge cold-formed steel compression members subjected to distortional buckling at elevated temperatures

Fire safety design of building structures has received greater attention in recent times due to continuing loss of properties and lives during fires. However, fire performance of light gauge cold-formed steel structures is not well understood despite its increased usage in buildings. Cold-formed steel compression members are susceptible to various buckling modes such as local and distortional buckling and their ultimate strength behaviour is governed by these buckling modes. Therefore a research project based on experimental and numerical studies was undertaken to investigate the distortional buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. Lipped channel sections with and without additional lips were selected with three thicknesses of 0.6, 0.8, and 0.95 mm and both low and high strength steels (G250 and G550 steels). More than 150 compression tests were undertaken first at ambient and elevated temperatures. Finite element models of the tested compression members were then developed by including the degradation of mechanical properties with increasing temperatures. Comparison of finite element analysis and experimental results showed that the developed finite element models were capable of simulating the distortional buckling and strength behaviour at ambient and elevated temperatures up to 800 °C. The validated model was used to determine the effects of mechanical properties, geometric imperfections and residual stresses on the distortional buckling behaviour and strength of cold-formed steel columns. This paper presents the details of the numerical study and the results. It demonstrated the importance of using accurate mechanical properties at elevated temperatures in order to obtain reliable strength characteristics of cold-formed steel columns under fire conditions.

Combined Distortional and Overall Flexural-Torsional Buckling of Cold-Formed Stainless Steel Sections: Design

This paper provides a critical summary of the European standards and design methods available for calculating the strength of cold-formed stainless steel compression members. The standards considered (so far mainly applied to columns failing by flexural buckling) are applied to the case of lipped channel section columns failing by combined distortional and overall flexural-torsional buckling. As observed during the tests presented in a companion paper, distortional buckling is found to have a considerable effect on the cross section resistance and is prone to interact with the global flexural-torsional mode. It is investigated how the different formulations account for the two buckling modes and their interaction and how accurate strength predictions they provide. A new direct strength method taking into account these failure modes is then presented and compared to the test results.

Unified Element and Section Approach to Design of Cold-Formed Steel Structures

Slender open-section cold-formed steel members that contain flanges with edge stiffeners may buckle in different modes and with mode interactions. The element design approach (effective width method) has been shown to produce unconservative capacity predictions for a particular class of such members. This paper presents a modification to the effective width method derived from an investigation of the fundamental behavior of edge stiffened flange elements and sections that contain them. The modified element design approach is validated against the results of 913 compression and bending members collected from the literature, where all section and member buckling modes and interactions were evident. A section design approach is also presented which is directly in line with the element approach. The unified element and section approach is shown to provide accurate and reliable design solutions for cold-formed steel compression and flexural members. Proposals for the North American specification for cold-formed steel structures are presented.

Combined Distortional and Overall Flexural-Torsional Buckling of Cold-Formed Stainless Steel Sections: Experimental Investigations

This paper presents a series of 48 full-scale tests on press-braked stainless steel lipped channel section columns subjected to concentric compression. The tests were carried out between fixed ends in the Structures Laboratory of the University of Liège and the test specimens were designed such that distortional buckling developed in the section prior to overall flexural-torsional buckling. The stainless steel alloy was 1.4003 chromium weldable steel, popularly known as 3Cr12. Three different geometries were tested using the same experimental setup. A critical summary of the standards and methods for calculating the carrying capacity of cold-formed stainless steel compression members is presented in a companion paper by the same writers.

Analysis and design of rehabilitated built-up hybrid steel compression members

Compression members in steel bridges designed before 1960 may be deficient according to current design code requirements and so require strengthening. This paper explores the response of steel wide-flange columns reinforced with new steel flange cover plates, accounting for: residual and locked-in dead-load stresses; different yield strengths of the original W shape and the new cover plates; initial out-of-straightness; and load eccentricity at the member ends. A refined numerical analysis model is formulated and validated that computes the compressive resistance from principles of equilibrium, compatibility, and force–deformation relationships. Parametric studies conducted indicate that the capacity of the reinforced column is relatively insensitive to the magnitude of the locked-in dead-load stress in the original member, and that the strong axis capacity is insensitive to the magnitude of the residual stresses in the original member. A preliminary approach for designing strengthening for these members is presented and illustrated with an example calculation.

Distortional buckling tests of cold-formed steel compression members at elevated temperatures

In recent times, light gauge cold-formed steel sections have been used extensively since they have a very high strength to weight ratio compared with thicker hot-rolled steel sections. However, they are susceptible to various buckling modes including a distortional mode and hence show complex behaviour under fire conditions. Therefore, a research project based on detailed experimental studies was undertaken to investigate the distortional buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. More than 150 axial compression tests were undertaken at uniform ambient and elevated temperatures. Two types of cross sections were selected with nominal thicknesses of 0.60, 0.80, and 0.95 mm. Both low (G250) and high (G550) strength steels were used. Distortional buckling tests were conducted at six different temperatures in the range of 20–800 ∘C. The ultimate loads of compression members subject to distortional buckling were then used to review the adequacy of the current design rules at ambient and elevated temperatures. This paper presents the details of this experimental study and the results.

The direct strength method for stainless steel compression members

The paper presents a complete set of direct strength equations for stainless steel members and sections in compression. The direct strength equations are based on recent research on the local, distortional and member bucking of stainless steel compression members, including the interaction of local and member buckling. The paper summarises the underlying research and presents the direct strength equations in a consistent format using a notation similar to that used in the North American Specification and the Australian Standard for (carbon) steel structures. Direct strength equations are proposed for local, distortional and combined local and member buckling, which fit within the framework of the Australian, North-American and European standards for stainless steel.

O.082 Dynamic ultrasonic examination in evaluation of the mandible regenerate development in children

Carbon fibre reinforced polymer (CFRP) has been used to strengthen steel members in bending and compression. There is a lack of understanding on behaviour of CFRP strengthened steel beams subject to torsion. This paper presents an experimental study on the behaviour of CFRP strengthened square hollow section (SHS) beams in pure torsion. A set of tests on CFRP strengthened steel specimens under torsion was carried out in which several different strengthening configurations were used. CFRP sheet wrapping consisted of different configurations including vertical, spiral, and reverse-spiral wrapping were used. The results showed that using CFRP could improve the elastic and plastic torsional strength of CFRP strengthened steel beam specimens. The number of layers of CFRP and the strengthening configurations were important factors for the improvement. Based on the measured values of the torsional moment at yielding and at ultimate, the corresponding twists, the torsional behavioural curves and the failure modes of the strengthened beam specimens, useful concluding remarks are presented.

Distortional Buckling of Cold-Formed Stainless Steel Sections: Experimental Investigation

This paper describes the experimental investigation of cold-formed, thin-walled stainless steel sections subject to distortional buckling under compression. Austenitic 304, ferritic 430 stainless steel, and ferritic-like 3Cr12 chromium weldable steel sheets were brake-pressed into simple-lipped channels and lipped channels with intermediate stiffeners. A full set of coupon tests reveal material nonlinearity with low proportionality stress and low n-parameter, anisotropy, and yield strength enhancements up to 2.33 times due to cold-forming. A total of 19 channel sections were tested and failed by distortional buckling at average ultimate stresses greater than the proportionality stress, and hence were influenced by material nonlinearity, with greater nonlinearity evident for sections with intermediate stiffeners. This paper presents comprehensive procedures to determine stainless steel mechanical properties and their influence on the distortional buckling mode of cold-formed sections. Experimental data required to calibrate finite element models and assess current design guidelines for distortional buckling of stainless steel compression members are provided herein.

Tests of cold-formed high strength stainless steel compression members

The paper describes a test program on cold-formed high strength stainless steel compression members. The duplex stainless steel having the yield stress and tensile strength up to 750 and 850 MPa, respectively, was investigated. The material properties of the test specimens were obtained from tensile coupon and stub column tests. The test specimens were cold-rolled into square and rectangular hollow sections. The specimens were compressed between fixed ends at different column lengths. The initial overall geometric imperfections of the column specimens were measured. The strength and behaviour of cold-formed high strength stainless steel columns were investigated. The test strengths were compared with the design strengths predicted using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures. Generally, it is shown that the design strengths predicted by the three specifications are conservative for the cold-formed high strength stainless steel columns. In addition, reliability analysis was performed to evaluate the current design rules.

Simplified design approach for cold-formed stainless steel compression members subjected to flexural buckling

The design criteria of stainless steel compression member are more complicated than those of carbon steels due to the nonlinear stress strain behavior of the material. In general, the tangent modulus theory is used for the design of cold-formed stainless steel columns. The modified Ramberg–Osgood equation given in the ASCE Standard can be used to determine the tangent modulus at specified level of stresses. However, it is often tedious and time-consuming to determine the column buckling stress because several iterations are usually needed in the calculation. This paper presents new formulations to simplify the determination of flexural buckling stress without iterative process. Taylor series expansion theory is utilized in the study for numerical approximations. The proposed design formulas are presented herein and can be alternatively used to calculate the flexural buckling stress for austenitic type of cold-formed stainless steel columns. It is shown that the column strengths determined by using the proposed design formulas have good agreement with those calculated by using the ASCE Standard Specification. A design example is also included in the paper for cold-formed stainless steel column designed by using the ASCE Standard equations and the proposed design formulas.

Rehabilitation of Compression Steel Members Using FRP Pipes Filled with Non-Expansive and Expansive Light-Weight Concrete

This paper presents the experimental and analytical evaluation of the feasibility of a proposed fiber reinforced polymer (FRP) retrofit method to strengthen corroded steel columns. This method consists of two steps: (1) wrapping the corroded steel column with an FRP jacket, and (2) filling the jacket with expansive light-weight concrete. Seven steel columns were tested in the laboratory including five strengthened columns with the proposed technique. The first two were used as control units where one was a virgin shape and the second was notched in the center zone to simulate the loss of section due to corrosion. The remaining five were all notched, and confined with FRP composite pipes within the simulated corroded zone and subsequently filled with light-weight concrete. All specimens were axially loaded to failure while strain and displacement readings were measured to demonstrate the feasibility of this repair concept. Test results show that the proposed FRP retrofit method for steel columns can be successfully applied. Furthermore, an analytical model was developed that can predict the load capacity of the FRP retrofitted steel column.

Using neural networks to predict the design load of cold-formed steel compression members

The paper considers the use of neural networks to predict the failure load of cold-formed steel compression members. The objective is to provide a fast method of predicting the failure load, so that the method can be used in other design algorithms, such as optimisation routines. Three types of symmetric sections are considered, and the results of neural network predictions compared with results from BS5950 Part 5. The results are in good agreement with the results from design codes. Moreover, a trained neural network gives the results significantly more quickly than a computer implementation of the code.

Effective design width for perforated cold-formed steel compression members

Perforations are often provided in the web and (or) flange plates of beams and columns of cold-formed steel (CFS) structural members in order to facilitate duct work, piping, and bridging. This paper is concerned with the establishment of effective design width equations for the determination of the ultimate strength of such perforated members in compression. A proven finite element model has been used to study the effects of perforation parameters on the ultimate strength of perforated members. The finite element model consists of short columns of lipped channel CFS sections, discretized using nonlinear "assumed strain" shell finite elements, and utilising experimental-based material properties models. The parametric study covers web slenderness values between 31 and 194, perforation width to web width ratios up to 0.6, and perforation height to perforation width ratios up to 3.0. Effective design width equations for plates having square perforations and elongated perforations were developed. The efficiency and accuracy of these two equations in predicting the ultimate strength of perforated CFS compression members have been verified through a comparison with the ultimate load results of several experimental studies from the literature.Key words: cold-formed steel, compressive loads, local buckling, perforations, finite element analysis, experimental, post-buckling strength, ultimate strength, effective width, design.