A Study on Cold-Formed Steel Compound Angle Section Subjected to Axial Compression

G. Beulah Gnana Ananthi 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.5

The objective of our work is to examine the compressive strength on pin-ended thin-walled steel built-up double angles placed as abox section. Four types of cross sections with two different thickness are chosen for this study. A total number of 16 columns bothstub and short columns are tested till they reach their ultimate strength. The built-up box angle sections consist of two identical lippedangle sections oriented face to face and connected with self-drilling screws through the lips in a particular spacing along the entirelength. By using the ABAQUS software, a numerical finite element is set up to validate initially by verifying the experimental dataon the behavior of built-up box angles. The Finite Element Model (FEM) holds both the geometric and material non-linearities. Astudy of parameter is done following the confirmation of the FEM on columns with different slenderness ratios ranging between 20to 120. The quantitative results showed that they agreed well with the data of the experiments. Comparison is made with the twoexperimental and the numerical outcomes using DSM (Direct Strength Method) strengths. A recommended design is put-forth usingDSM to calculate the eventual load carrying capacity for the built-up box angle sections.

Experimental and numerical investigations on axial strength of back-to-back built-up cold-formed steel angle columns

G. Beulah Gnana Ananthi,Krishanu Roy,James B.P. Lim 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.31 No.6

In cold-formed steel (CFS) structures, such as trusses, wall frames and columns, the use of back-to-back built-up CFS angle sections are becoming increasingly popular. In such an arrangement, intermediate fasteners are required at discrete points along the length, preventing the angle-sections from buckling independently. Limited research is available in the literature on the axial strength of back-to-back built-up CFS angle sections. The issue is addressed herein. This paper presents the results of 16 experimental tests, conducted on back-to-back built-up CFS screw fastened angle sections under axial compression. A nonlinear finite element model is then described, which includes material non-linearity, geometric imperfections and explicit modelling of the intermediate fasteners. The finite element model was validated against the experimental test results. The validated finite element model was then used for the purpose of a parametric study comprising 66 models. The effect of fastener spacing on axial strength was investigated. Four different cross-sections and two different thicknesses were analyzed in the parametric study, varying the slenderness ratio of the built-up columns from 20 to 120. Axial strengths obtained from the experimental tests and finite element analysis were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparison showed that the DSM is over-conservative by 13% on average. This paper has therefore proposed improved design rules for the DSM and verified their accuracy against the finite element and test results of back-to-back built-up CFS angle sections under axial compression.

Testing, simulation and design of back-to-back built-up cold-formed steel unequal angle sections under axial compression

G. Beulah Gnana Ananthi,Krishanu Roy,Boshan Chen,James B.P. Lim 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.4

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material nonlinearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.

Tests and Finite Element Modelling of Cold-Formed Steel Zed and Hat Section Columns Under Axial Compression

G. Beulah Gnana Ananthi,Krishanu Roy,James B.P. Lim 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.4

This paper presents an experimental and numerical investigation into the buckling behaviour of axially loaded cold-formed steel (CFS) zed and hat sections. In total, 12 experimental tests are reported, of those 6 tests are on CFS zed sections and the remaining 6 are on CFS hat sections. The failure modes, ultimate loads, and load–displacement curves of the specimens were reported and analyzed. The experiments revealed the deformation mechanism of both the zed and hat sections failing in distortional mode. Nonlinear fi nite element (FE) models are then described for both the zed and hat sections, which include material non-linearity and geometric imperfections. The validated fi nite element models were then used for the purpose of parametric studies comprising 140 models, which include 70 models each for CFS zed and hat sections. Ten diff erent crosssections were analyzed in the parametric study for both the zed and hat sections. The axial strengths obtained from the experimental tests and FE analysis were used to assess the performance of the current design guidelines as per the Direct Strength Method for both the zed and hat sections. From the comparison, it was found that the design strengths are un-conservative by 7% and 10% on average for CFS zed and hat sections, respectively. An improved design equation was therefore proposed for those CFS zed section columns, which failed by either distortional buckling or through a combination of distortional and global interactive buckling. The proposed equation gave a close comparison against FE results, being conservative to the FE results by only 3%. Reliability analysis was also performed to confi rm the reliability of the proposed design equation.

Behaviour and strength of back-to-back built-up cold-formed steel unequal angle sections with intermediate stiffeners under axial compression

G. Beulah Gnana Ananthi,Krishanu Roy,James B. P. Lim 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.1

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-toback built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation reported by the authors on back-to-back built-up CFS unequal angle sections with intermediate stiffeners under axial compression. The load-axial shortening behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated finite element model was then used for the purpose of a parametric study comprising 96 models to investigate the effect of longer to shorter leg ratios, stiffener provided in the longer leg, thicknesses and lengths on axial strength of back-toback built-up CFS unequal angle sections. Four different thicknesses and seven different lengths (stub to slender columns) with three overall widths to the overall depth (B/D) ratios were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% and 5% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections with and without the stiffener, respectively.

Experimental and numerical study of an innovative 4-channels cold-formed steel built-up column under axial compression

Beulah Gnana Ananthi G,Krishanu Roy,James B. P. Lim 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.4

This paper reports on experiments addressing the buckling and collapse behavior of an innovative built-up coldformed steel (CFS) columns. The built-up column consists of four individual CFS lipped channels, two of them placed back-toback at the web using two self-drilling screw fasteners at specified spacing along the column length, while the other two channels were connected flange-to-flange using one self-drilling screw fastener at specified spacing along the column length. In total, 12 experimental tests are reported, covering a wide range of column lengths from stub to slender columns. The initial geometric imperfections and material properties were determined for all test specimens. The effect of screw spacing, load-versus axial shortening behaviour and buckling modes for different lengths and screw spacing were investigated. Nonlinear finite element (FE) models were also developed, which included material nonlinearities and initial geometric imperfections. The FE models were validated against the experimental results, both in terms of axial capacity and failure modes of built-up CFS columns. Furthermore, using the validated FE models, a parametric study was conducted which comprises 324 models to investigate the effect of screw fastener spacing, thicknesses and wide range of lengths on axial capacity of back-to-back and flange-to-flange built-up CFS channel sections. Using both the experimental and FE results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australia/New Zealand (AS/NZS) standards is slightly conservative by 6% on average, while determining the axial capacity of back-to-back and flange-to-flange built-up CFS channel sections.

Effect of web hole spacing on axial capacity of back-to-back cold-formed steel channels with edge-stiffened holes

Yaohui Chi,Krishanu Roy,Boshan Chen,Zhiyuan Fang,Asraf Uzzaman,G. Beulah Gnana Ananthi,James B.P. Lim 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.2

Recently, a new generation of cold-formed steel (CFS) channel section with edge-stiffened web holes has been developed by industry in New Zealand. However, no research has been reported in the literature to investigate the axial capacity of back-to-back channels with edge-stiffened web holes. This paper presents a total of 73 new results comprising 29 compression tests and 44 finite element analyses (FEA) on axial capacity of such back-to-back CFS channels. The results show that for back-to-back channels with seven edge-stiffened holes, the axial capacity increased by 19.2%, compared to plain channels without web holes. A non-linear finite element (FE) model was developed and validated against the test results. The validated FE model was used to conduct a parametric study involving 44 FE models. Finely, the tests results were compared with the design strengths calculated from the AISI and AS/NZ standards and from the proposed design equations of Moen and Schafer. From the comparison results, it was found that the AISI and AS/NZ design strengths are only 9% conservative to the test results for plain channels without web holes. While Moen and Schafer equations are conservative by 13% and 47% for axial capacity of CFS back-to-back channels with un-stiffened and edge-stiffened web holes, respectively.