Pseudo-plastic Collapse Performance of Multi-span Continuous Beams with CFS Sigma Sections: A Numerical Study

Local buckling behaviour of web perforated cold-formed steel lipped channel columns

The cold-formed steel (CFS) double-lipped equal-leg angle is widely used in modular container houses and cold-formed steel buildings. To study the buckling behavior and bearing capacity design method of the cold-formed steel (CFS) double-lipped equal-leg angle under axial compression, 24 CFS double-lipped equal-leg angles with different sections and slenderness ratios the axial compression were conducted. The test results showed that the distortional buckling occurs for specimens with a small width-to-thickness ratio and small slenderness ratio. The buckling interactive with distortional and global flexural buckling was observed for the specimens with small width-to-thickness ratios and large slenderness ratios. The specimens with large width-to-thickness ratios and small slenderness ratios showed interactive buckling with local and distortion buckling. The specimens with large width-to-thickness ratios and large slenderness ratio developed interactive buckling with local, distortional, and global flexural buckling. The finite element model established by ABAQUS software was used to simulate and analyze the test. The buckling modes and the load-carrying capacities analyzed by the finite element model agreed with the test results, which showed that the developed finite element model was feasible to analyze the buckling and bearing capacity of the CFS double-lipped equal-leg angles. The experimental results were compared with those calculated by the direct strength method in the North American standard and the effective width method in the Chinese standard. The comparisons indicated that the calculated results are very conservative with maximum value 36% and 51% for direct strength method and effective width method, respectively. The coefficient of variation was 0.276 and 0.397, respectively. Finally, the modified direct strength method and the modified effective width method were proposed based on the experimental results. The comparison on the ultimate strength between test results and calculated results by using the modified method showed a good agreement. The modified method can be as a proposed desigh method for the ultimate strength of the CFS double-lipped equal-leg angles under axial compression.

Local–distortional buckling mode of steel cold-formed columns: Generalized direct strength design approach

For the distortional buckling of cold-formed thin-wall steel members, the Direct Strength Method (DSM) is a recently adopted design approach by foreign standard, and Chinese professional standard Technical specification for low-rise cold-formed thin-wall steel buildings present the calculation formulas based on the Effective Area Method (EAM) .The key of both methods is the elastic distortional buckling stress .At present, the calculation methods about it are over conservative .Compare the calculation results of method in AISI S100with the one calculated by software CUFSM ,for C and Z sections in bending and axial compression loading respectively in the North American Specifications for Cold-Formed Steel Structural Members (AISI S100). This paper presents revised simplified methods for calculating the elastic distortional buckling stress. The new methods yield more accurate results but similar computation cost compared to the existing methods.

Cold-formed steel members have been used extensively in low and mid-rise residential building construction. The usage of cold-formed steels as primary structural members has been increased due to its high load to weight ratio. Cold-formed steel built-up sections are commonly used as compression elements to carry larger loads and over longer spans when a single individual section is insufficient. However, not much research has been done on built-up sections. This paper aims to investigate the compressive capacity of pin-ended cold-formed steel built-up lipped channel sections using finite element analysis (FEA). In the study, cold-formed steel built-up lipped channel consists of two identical C-channel sections oriented back to back with spacing between them and having a ratio of Ixx = Iyy which are connected by battens at top and at bottom throughout its lengths at regular intervals according to code based provisions. A non-linear finite element model is developed and verified against theoretical results. The thickness of the members is thin and hence they are susceptible to buckling, shell elements S4R are used in FE modeling. The theoretical analysis is based on effective width method and direct strength method and the results are generally conservative for cold-formed steel built-up channel sections.

Load-bearing cold-formed steel (CFS) wall panels comprise of a stud (C-section), track (U-section) and sheathing. Sheathing is fastened to the CFS frame with self-drilling screws, which has an effect on the axial load-carrying capacity of panels. Experiments are complex and often expensive as they require use of different resources (raw material, manpower etc.). Therefore, conducting experiments is not always possible and an efficient design tool is necessary. Few studies are present in literature on comparing the effectiveness of available design methodologies. For the first time, an attempt is made to compare all the three (03) presented mathematical models together to predict the axial strength of CFS wall panels with sheathing. The present study examines the effectiveness of such analytical/semi-analytical tools, namely, Rayleigh-Ritz (R-R) method, Differential equation of equilibrium (DEEq) method and Constrained and Unconstrained Finite Strip Method – Direct Strength Method (CUFSM-DSM) for estimation of axial load-carrying capacity of sheathed CFS panels. The results show that CUFSM-DSM can be utilized meritoriously for evaluation of sheathed CFS wall panels.

Self-drilling screws are the primary means of fastening for cold-formed steel members in cold-formed thin-gauge steel residential construction because it can drill their own holes and form their own threads. The fabrication of connections is the most labour intensive aspect of the cold-formed thin-gauge steel construction process, thus a better understanding of the behaviour of screw connections could lead to optimum connection design and reducing the cost of the fabrication. The study carried out to investigate the behaviour of single-shear connections using self-drilling screws in the cold-formed steel construction. The focus of this study is on the influence of the number of screws and screw spacing on the strength of self-drilling screw connection. These parameters are varied to determine their influences on the connection strength. The failure load and failure modes were obtained and observed from the tests carried out in the laboratory. Bearing and tilting failures occurred during the testing of these specimens. The predicted connection strengths were calculated using American Iron and Steel Institute (AISI) design equations. A total of 24 specimens of single shear test showed that connection strength is linearly proportional to the number of screw in the connection. Results of the specimen with spacing more than 3d show better correlation with the calculated results as compared to specimens with screw spacing less than 3d.

Local buckling studies of cold-formed steel compression members at elevated temperatures

Experimental and numerical studies of fire exposed lipped channel columns subject to distortional buckling

Effect of manufacturing process on microstructures and mechanical properties, and design of cold-formed G450 steel channels

The ultimate carrying capacity of axially loaded welded square box section members made of medium and high strength steels (nominal yield stresses varying from 345 MPa to 460 MPa), with large width-to-thickness ratios ranging from 35 to 70, is analyzed by finite element method (FEM). At the same time, the numerical results are compared with the predicted results using Direct Strength Method (DSM), modified DSM and Effective Yield Strength Method (EYSM). It shows that curve a, rather than curve b recommended in Code for design of steel structures GB50017-2003, should be used to check the local-overall interaction buckling strength of welded square section columns fabricated from medium and high strength steels when using DSM, modified DSM and EYSM. Despite all this, EYSM is conservative. Compared to EYSM and modified DSM, DSM provides a better prediction of the ultimate capacities of welded square box compression members with large width-thickness ratios over a wide range of width-thickness ratios, slenderness ratios and steel grades. However, for high strength steels (nominal yield strength greater than 460 MPa), the numerical and existent experimental results indicate that DSM overestimates the load-carrying capacities of the columns with width-thickness ratio smaller than 45 and slenderness ratio less than 80. Further, for the purpose of making it suitable for a wider scope, DSM has been modified (called proposed modified DSM). The proposed modified DSM is in excellent agreement with the numerical and existing experimental results.

This paper reports the available results of an ongoing numerical investigation on the buckling, post- buckling, collapse and design of two-span cold-formed steel lipped channel beams subjected to uniformly distributed loads. The results presented and discussed are obtained through analyses based on Generalised Beam Theory (elastic buckling analyses) and shell finite element models (elastic and elastic-plastic post-buckling analyses up to collapse). Moreover, the ultimate loads obtained are used to establish preliminary guidelines concerning the design of continuous (multi-span) cold-formed steel beams failing in modes that combine local, distortional and global features. An approach based on the existing Direct Strength Method (DSM) expressions is followed and the comparison between the numerical and predicted ultimate loads makes it possible to draw some conclusions concerning the issues that must be addressed by a DSM design procedure for cold-formed continuous beams.

The Direct Strength Method (DSM) design rules for cold-formed steel members have been incorporated recently into the North American specification for the design of cold-formed steel structural members (AISI S100-12) and the Australian cold- formed steel structures standard (AS/NZS 4600:2005). The method covers the design of structures with and without holes subjected to compression and bending and without holes for shear. Recent research has extended the DSM to the design of beams with holes predominantly in shear. This paper reviews the DSM design guidelines for perforated members in compression and bending and the latest research on the DSM for perforated beams in shear.

The main objective of this research is to extend the “Direct strength method” for determining the web crippling strength of cold-formed steel C and Z sections subjected to End one flange loading and Interior one flange loading conditions. Direct strength method is applied for designing the columns and beams earlier. The existing specifications equation for calculating the web crippling strength of cold-formed steels designed by American Institute of Iron and Steel is very old method and it is based on the extensive experimental investigations conducted at different universities. Calculating the web crippling strength of cold-formed steels using direct strength method is a new technique. In the present research the web crippling strength of cold-formed steels were calculated using Direct Strength Method. The experimental data is collected from the tests that were conducted at different universities. The critical buckling strength of the members were calculated using Abaqus. Microsoft excel is used to generate the equations. The safety and resistance factors for the designed equations were calculated using “Load and resistance factor design” and “Allowable strength design” from North American Cold-Formed Steel Specification, 2012 edition book.

Cold-formed steel sections are becoming popular for different steel structures, because they have a high resistance against different straining actions, with a minimal weight compared with hard steel sections. Recently, perforated cold-formed steel (PCFS) sections have been used in many applications, such as perforated upright storage racks. Experimental research into the behavior of steel storage rack uprights subjected to axial compression is presented in this paper. First, tensile tests determined the material qualities of the cold-formed steel uprights. Then, seventeen perforated specimens were examined under axial compression, with five different cross-sections, three different web heights and thicknesses, and varying lengths. The study’s goals were to find out how perforations affect the performance and failure mode of steel storage rack uprights, to discuss the interaction of distortional and global buckling, and to verify the accuracy of using the direct strength method (DSM) for predicting the ultimate strength before failure in buckling interactions for perforated uprights. It was found that the failure modes of perforated specimens with stiffeners generally cannot be well predicted using the direct strength method. However, when the modifications proposed by Xianzhong Zhao et al. are used, the accuracy is acceptable.