Cold-formed Sections Research Articles

Flexural behaviour of cold-formed steel oval hollow section beams

This paper presents a detailed investigation into the flexural strength and behaviour of cold-formed steel oval hollow section beams. A series of four-point bending tests were conducted as part of the experimental programme. Following this, a total of 12 tested beams were simulated by a non-linear finite element analysis. Upon validation of the newly developed numerical model, a total of 36 numerical results were generated through a parametric study to assess the structural response of the oval hollow section beams over a wider range of cross-section dimensions. The experimental and numerical data were used to evaluate the applicability of five existing design methods for cold formed steel structural members, including Eurocode 3, the North American Specification, the Australian/New Zealand Standards, the direct strength method and the continuous strength method. In general, the results indicate that all the three design standards produce unconservative predictions, while the direct strength method and the continuous strength method yield relatively accurate and consistent predictions.

Pengaruh Jarak Sekrup terhadap Kapasitas dan Perilaku Penampang Tersusun Boks (Closed Section) Baja Canai Dingin

The capacity and behaviour of cold-formed steel built-up sections are affected by the arrangement of the connections. This study aims to determine the effect of the screw spacing to the bending capacity and behaviour of the cold-formed steel built-up box section which made from lipped-channel (1.0 mm thick, 81 mm web height, 8.5 mm lip height, upper and lower wing width 38 mm and 40 mm). A total of 19 beams with a length of 1200 mm each are subjected to pure bending moments by applying two point loads spaced 600 mm in the midspan. The screw spacing variations in the moment span are 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 328 mm, and 350 mm. The test results show the average of bending capacity of the beam test is increasing with the reduction in screw spacing while the screw configuration also affects the beam capacity. Analysis of the bending capacity using the effective width method and the direct strength method based on AISI S100-16 gives very conservative results. The failure mode of the built-up box sections were observed in the form of local buckling, distortion, and lateral-torsional buckling.

Impact of Geometrical Imperfections on Estimation of Buckling and Limit Loads in a Silo Segment Using the Vibration Correlation Technique.

The paper examines effectiveness of the vibration correlation technique which allows determining the buckling or limit loads by means of measured natural frequencies of structures. A steel silo segment with a corrugated wall, stiffened with cold-formed channel section columns was analysed. The investigations included numerical analyses of: linear buckling, dynamic eigenvalue and geometrically static non-linear problems. Both perfect and imperfect geometries were considered. Initial geometrical imperfections included first and second buckling and vibration mode shapes with three amplitudes. The vibration correlation technique proved to be useful in estimating limit or buckling loads. It was very efficient in the case of small and medium imperfection magnitudes. The significant deviations between the predicted and calculated buckling and limit loads occurred when large imperfections were considered.

Nonlinear behavior of cold-formed stainless steel built-up box sections under axial compression

Stainless steel is a highly versatile material, possessing a unique selection of properties that can be exploited in structural (load bearing) applications. In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of built-up cold-formed stainless steel box sections as compression members are becoming popular. The AISI/ASCE Standard, SEI/ASCE-8–02 and AS/NZS do not include the design of stainless-steel built-up channels and very few experimental tests or finite element analyses have been reported in the literature for such face to-face cold-formed stainless-steel channel box sections. Thus, this paper presents a numerical investigation on the behavior of cold-formed stainless-steel built-up channel box sections. Three different grades of stainless steel i.e., duplex EN1.4462, ferritic EN1.4003 and austenitic EN1.4404 were considered. Effect of screw spacing on the axial strength of such built-up channel box sections was investigated. As expected, most of the short and intermediate columns failed by either local–global buckling interaction or just by local buckling, whereas the long columns, failed by global buckling. A comprehensive parametric study was carried out covering a wide range of slenderness and different cross-sectional geometries to assess the performance of the design guidelines by AISI and AS/NZS. In total, 180 finite element models were analyzed. From the results of the parametric study, it was found that the AISI and AS/NZS are conservative by around 15% for duplex grade (EN1.4462) of stainless-steel built-up box columns. However, for ferritic (EN1.4003) and austenitic (EN1.4404) grades of stainless-steel built-up box columns, the AISI and AS/NZS were conservative by only 5%.

Effect of Partial Closing of the Open Face of Cold-Formed Steel Channel Sections

This document presents the effect of partial closing of the open face of cold formed steel channel. From the past, closed sections are favourably used in CFS for framing applications. Open sections, like channels offer good moment resistance and also offer a clean and flat surface on the outside of the web but when loaded in vertical direction cause twist in the channel section since the loading is not through the shear centre. This twist also causes lateral deflection of the section at the level of the two flanges. In order to restrain and minimize the lateral torsional bucking, an experimental and numerical trial has been performed on the channels which are covered with plate along the length of the beam by 1/3rd, 2/3rd and full cover plate of the beam channel and compared. Specimens with 2/3rd and full length cover plate along the length show improved resistance against lateral deflection and torsion. The performance reduces as length of the beam increases. The specimens of 2/3rd length cover plate show almost equal performance to the specimens of full length cover plate. As a result, 2/3rd cover plate beam can be efficiently used to serve the purpose for better efficiency. Numerical models are developed and compared with the experimental results. Following a series of analyses, it is found that in general, the effect of the covering is more significant on longer specimens. Conclusions derived based on the experimental and numerical results also point to the definite improvement by the partial closing of the channel sections.

Axial capacity of back-to-back built-up cold-formed stainless steel unlipped channels-Numerical investigation and parametric study

In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of back-to-back built-up cold-formed stainless steel unlipped channels as compression members are becoming popular. The advantages of using stainless steel as structural members are corrosion resistance and durability, compared with carbon steel. Current guidance by the American Iron and Steel Institute (AISI) and the Australian and New Zealand (AS/NZS) standards for built-up carbon steel sections describes a modified slenderness approach, to consider the spacing of the intermediate fasteners. The AISI and AS/NZS do not include the design of stainless-steel built-up channels and very few experimental tests or finite element (FE) analyses have been reported in the literature for such back-to-back cold-formed stainless steel unlipped channel section columns. This paper presents a numerical investigation on the behavior of back-to-back built-up cold-formed stainless steel unlipped channel section columns. Three different grades of stainless steel i.e., duplex EN1.4462, ferritic EN1.4003 and austenitic EN1.4404, were considered. The effects of screw spacing on the axial strength of such built-up unlipped channels were investigated. As expected, most of the short and intermediate columns failed by either local-global or local-distortional buckling interactions, whereas the long columns failed by global buckling. All three grades of stainless-steel stub columns failed by local buckling. A comprehensive parametric study was then carried out covering a wide range of slenderness and different cross-sectional geometries to assess the performance of the current design guidelines of carbon steel built-up sections in accordance with the AISI and AS/NZS. In total, 647 FE models were analyzed. From the results of the parametric study, it was found that the AISI and AS/NZS are conservative by around 14 to 20% for all three grades of stainless steel built-up unlipped channel section columns failed through global buckling. However, the AISI and AS/NZS carbon steel design rules can be un-conservative by around 8 to 13%, when they are used to calculate the axial capacity of those stainless steel built-up unlipped channels which are failed in local buckling.

Flexural behaviour of cold-formed steel built-up section members

Flexural behaviour of cold-formed steel built-up section members

Experimental study on the axial bearing capacity of built-up cold-formed thin-walled steel multi-limb-section columns

To solve the shortcomings of single-limb or double-limb cold-formed thin-walled steel column easy to buckling failure and low bearing capacity, a new cross-shaped built-up cold-formed thin-walled steel multi-limb-section is proposed for columns. The structure is composed of several single-limb cold-formed thin-walled steel C-channel sections. The flanges and webs are connected by self-drilling screws. In order to assess the mechanical properties of this built-up multi-limb-section column and the influence of the slenderness ratio on the column behavior, the axial loading tests were carried out. Three kinds of single-limb column and built-up multi-limb-section column with different ratio of slenderness were tested. The deformation process, failure mode and bearing capacity were analyzed. The SC specimens failed with local buckling and distorted buckling, while the MC and LC specimens failed with local buckling and global instability. For the built-up multi-limb-section column, the section combination multiple is 12. Compared to the section combination multiple, the bearing capacity combination multiple is much higher. The SQ specimens' combination factor is about 1.1, the combination factor of MQ specimens and LQ specimens are about 1.4 and 3.0, respectively. It is concluded that the overall combined-performance and structural efficiency of the specimens is proportional to the combination factor.

Parametric study and Improved design guidelines of CFS battened built-up columns

This paper presents the parametric study on the strength and behaviour of CFS closed built-up battened columns. The CFS closed built-up battened column consists of two lipped channels placed face-to-face with a uniform spacing of battens. Finite element models are validated with the results of the test specimens available in the thesis of the first author. The parametric study on 176 cold-formed steel built-up column sections is extended by using the validated finite element modeling covering a wide range of global column slenderness, plate slenderness and yield stress. The numerical results from the parametric study are compared with the design strengths calculated by the European specifications (EN1993-1-3:2006) and AISI Specifications (AISI S100:2016). The comparison of parametric results with the design strength predictions has indicated the design guidelines of the specifications need improvement. The design strength predictions of the specifications are also assessed by conducting the reliability analysis. Therefore, the exiting design rules are modified to improve the accuracy of the design strength predictions for the CFS closed built-up battened columns subjected to the axial compression. Furthermore, the reliability of the proposed methods is confirmed by means of reliability analysis.

Experimental and numerical investigation of short GFRP- reinforced steel tubular short columns

Abstract This study presents the experimental and analytical modelling of externally bonded glass fibre-reinforced polymer (GFRP) sheets for strengthening circular steel tubular short columns. The GFRP sheets are easy to handle due to the lightweight property and the high-strength can provide a degree of restraint to delay buckling of the thin steel wall. Four short columns of cold-formed steel circular hollow section (CHS) were experimentally tested. One column is conventional (without GFRP wrap) and other 3 columns are externally bonded unidirectional (hoop) GFRP sheets which are varying with numbers of layers (1, 2 and 3 layers). In addition to the experimental studies, finite element analysis was also carried out using ABAQUS software. The experimental result shows that the steel tube is strengthened by GFRP sheets and enhances the axial section capacity. The load carrying capacity of externally bonded GFRP column increases about 17%−49% on comparison with the column without confinement. The study also concluded that the column externally warped with 3 layers of GFRP sheet is found to be optimum and it attains maximum load caring capacity. The prediction of analytical results has been found to be in good correlation with the experimented results.

Residual stress measurements and modeling of built-up Box-T sections

Increasing use has been made recently of special-shaped columns (i.e., L-shaped, T-shaped, and cross-shaped) in multistory and high-rise residential and official buildings, due to their advantages in avoiding column protrusion and enlarging the indoor space. The box-T section column, built up by one cold-formed box section and several welded or hot rolled T-sections, is a new special-shaped column type. In this paper we report an experimental investigation of the residual stress distributions of eight box-T sections using the sectioning method, including L-shaped and T-shaped columns. From the experimental results, new residual stress distribution patterns for welded box-T sections and rolled box-T sections are found. Based on the interaction analysis of the residual stresses in different components of box-T sections, reasonable assumptions and simplifications for the residual stress distribution patterns are obtained. Finally, residual stress distribution models are proposed for welded box-T sections and rolled box-T sections and they are verified by finite element (FE) analysis to meet the self-equilibrium condition. The proposed residual stress distribution models can be used in the buckling analysis of box-T section columns and the modeling concepts in this paper may be invoked in the processes for modeling residual stress distributions in other complex built-up sections.

Constrained optimization of anti-symmetric cold-formed steel beam-column sections

Flexibility in the manufacturing of cold-formed steel (CFS) cross-sectional shapes provides a unique opportunity to improve the load-carrying capacity of these elements, leading to more efficient and economic structural systems. This paper presents a practical constrained optimization methodology for pin-ended anti-symmetric CFS beam-columns members with different lengths subjected to various combinations of axial compression and bending moment. The optimization process is carried out using a Genetic Algorithm (GA) with respect to buckling resistance of CFS elements determined according to the Direct Strength Method (DSM). In total, 132 CFS beam-columns with three different lengths (1000, 2000 and 3000 mm) and eleven different cross-sections are optimized under concentrically compressive loads with different levels of eccentricities varying from 0 to 30 mm. Each cross-section is formed using a certain number of fold-lines of steel plate, while the length and angle of the constituent elements of the cross-section are considered as the main design variables. To provide more practical beam-column elements, end-use constraints as well as a range of practical manufacturing and construction limitations are imposed on the selected cross-sections during the optimization process. A standard commercially available anti-symmetric Z section is taken as a starting point of optimization and used to assess the efficiency of the optimized sections. The results show that, for the given plate width and thickness, the adopted optimization process can significantly increase the strength of beam-column members on average 62%, 92%, and 188% for the short, medium and long length elements, respectively, compared to those with the standard section. It is also demonstrated that using more complex cross-sectional shapes does not necessarily provide higher strength for beam-column members. Finally, to verify the efficiency of the optimized sections, detailed nonlinear finite element models are developed using ABAQUS software. The developed models should prove useful for the efficient design of CFS beam-column elements in practice.

Test and design of stainless steel K-joints in cold-formed circular hollow sections

Stainless steel structures have obvious competitive advantages for buildings in the corrosive environment. In recent years, many studies have been conducted on the behaviors of stainless steel materials and members, but the behaviors of joint were rarely reported. This study carried out nine tests on stainless steel K-joints in cold-formed circular hollow sections. The material properties of circular hollow sections, the ultimate loads, the failure modes, and the load-deflection curves of joint were all reported. All the joints failed in the chord plastification. Finite element models were developed for K-joints, and were validated using the test data. Parametric studies were then conducted. Totally, 720 finite element models were built, and the effects of the geometric configuration, the chord preload, and the chord material properties on the joint capacity were explored. Based on the results of the parametric studies, the parameter Qu accounting for the influence of geometric configurations (i.e. β, γ, and g) and the parameter Qf accounting for the influence of chord preload were modified based on the corresponding formulae in the CIDECT design guide for low-carbon steel K-joints. To further improve the accuracy of prediction, a new parameter Qy400 was proposed to consider the effect of the chord material property variations. The predictions of the proposed were compared with test data collected in literature. It is concluded that the proposed design formulae have good performances in predicting the capacity of stainless steel K-joint in circular hollow section.

Flexural-torsional buckling of cold-formed steel columns with arbitrary cross-section under eccentric axial load

In recent years, the use of cold-formed steel sections as load bearing components has increased significantly. These sections are susceptible to a variety of cross-section instabilities, including local, distortional, global or a combination of these buckling modes due to their low thickness, so it is necessary to investigate the buckling behavior of these members. In this paper, the flexural–torsional buckling behavior of cold-formed steel columns with arbitrary asymmetric cross section has investigated. For this purpose, using the exact static stiffness matrix method, the differential equations governing column buckling with arbitrary asymmetric cross section have been extracted under eccentrically axial load. Calculating buckling loads using this method results in a nonlinear eigenvalue problem. For solve this problem, Wittrick- Williams algorithm is used. The extracted formulation is predicted to be used to calculate the critical loads of the types of double symmetric, single symmetric and asymmetric cold-formed sections.

Numerical simulation and design of stainless steel hollow flange beams under shear

Stainless steel offers a range of benefits over conventional carbon steel in structural applications. This paper presents the detailed numerical modelling of shear response of cold-formed stainless steel hollow flange sections using finite element software package, Abaqus. The effect of geometric parameters such as section height and section thickness, and the influence of different steel grades were investigated following the validation of finite element models. From numerical results, the formation of diagonal tension fields can be clearly observed in the webs of rectangular hollow flange sections while more even distribution of the stresses in the webs is seen in triangular hollow flange sections. Further, a plastic hinge type mechanism is formed in triangular flanges at the post-failure region. The evaluation of Eurocode 3 and the direct strength method shear design provisions for stainless steel hollow flange beams is found to be significantly conservative. Therefore, modified provisions were proposed and the comparison of those with finite element results confirmed the accurate and consistent shear resistance predictions over the codified provisions.

Stub Column Behavior of Cold-Formed High-Strength Steel Circular Hollow Sections under Compression

AbstractThis paper describes an experimental and numerical investigation on the stub column behavior of cold-formed high-strength steel (HSS) circular hollow sections (CHSs). A total of 16 stub col...

Cross-sectional behaviour of cold-formed high strength steel circular hollow sections

A comprehensive experimental and numerical study into the cross-sectional behaviour of structural steel circular hollow sections (CHS), with an emphasis on high strength steel, is presented in this paper. Six cold-formed high strength steel S700 CHS profiles – 168.3×4, 139.7×4, 139.7×5, 139.7×6, 139.7×8 and 139.7×10 (diameter × thickness, in mm), spanning from Class 1 to Class 4 in compression according to EN 1993-1-1, were experimentally examined. The test programme consisted of twelve tensile coupon tests, local geometric imperfection measurements, six stub column tests, six four-point bending tests, six three-point bending tests and fifteen short beam-column tests. In parallel with the experimental study, finite element (FE) models of CHS were established and validated against the obtained experimental results, and parametric studies were subsequently carried out using the developed models to expand the cross-sectional resistance data pool. Finally, the cross-section design provisions specified in the European code prEN 1993-1-1:2018 and the American Specification ANSI/AISC 360-16 were assessed using the freshly generated experimental and numerical results as well as the existing test data on hot-rolled and cold-formed CHS from the literature. The present study provides the basis for the development of improved cross-section design rules for normal and high strength steel CHS in future research.

Study on Ultimate Strength and Buckling Modes of Cold Formed Steel Structures

Stronger construction material is category from one of the steel structure are attain higher strength with stand the resistance of steel by natural as well as it could made in different shapes. The exact shape of steel structure and its profile are precisely designed from cross section to ensure Indian Standard along with mechanical and chemical characteristics. All over the country’s most of the industrialization is precise on sizes, shapes; strengths, storage practices and its composition of steel structure are used as per standards. cold-formed steel is effect with rolling of thin gauge steel sheet increasing the yield strength whose products are widely used in construction industries, as well as structure like columns, beams, joists, studs, floor decking, built-up section, telecommunication towers, electricity transmission steel tower, multi-storied steel structures, etc., due to its stronger and reduction in dead weight cold-formed steel is used. The dies are series of making various section of cold-formed steel structural member with different section and shapes by cold roll forming the steel to attain the preferred shape. As per the standard, nominal minimum yield strength of sheet steel rolled in cold-formed section is 250 N/mm2. However, user trend use of greater strength, but it could be lesser as 230 N/mm2.

Effect of staggered bolted connections on CFS channel sections

This research focuses on the effect of staggered bolted connections on the ultimate tensile capacity and failure modes of the cold-formed steel channel sections connected to the gusset plates. The test program includes two series of 113 channel specimens tested under axial tension with one series containing 52 two-bolted specimens and the other with 61 three-bolted specimens. All the specimens were bolted in the web in a staggered fashion, and the main parameters being investigated are different channel dimensions, staggered and gauge distances, and bolt hole diameter. The test results indicate that the tensile resistance of the two-bolt staggered connection is usually bearing controlled and that of the three-bolt staggered connection is net-section rupture. In addition, the original formula s2/(4g + 2dh) proposed by Cochrane is used to calculate the net section area, instead of simplified s2/4g, which could overestimate the net section area upto 10%. Furthermore, the net-section efficiency factor proposed in codes such as EN-1993-1-3, AS/NZS 4600: 2018, and literature to account for in-plane and out-of-plane shear lag, and bending moment due to the eccentricity in loading is evaluated with the test results from three-bolt configurations obtained from this study. It was observed that the current code provisions (EN-1993-1-3:2004, AS/NZS 4600:2018) for staggered bolt configuration yield non-conservative estimates of the ultimate tensile strength. However, the latest equation proposed by Teh and Gilbert [1] (also adopted in AISI 2016), which accounts for all the sources of capacity reduction factors mentioned above, predicted the net section tension capacity accurately. Through the reliability analysis of the equation by Teh and Gilbert [1] based on the present test results, the resistance factor of 0.75 for LRFD and safety factor of 2.05 for ASD design philosophies are suggested.

Critical Buckling Strains in Thick Cold-Formed Circular-Hollow Sections under Cyclic Loading

AbstractContrary to the large dataset of test results exploring the monotonic bending response of steel tubes, the corresponding dataset of cyclic bending tests remains very small. Seven compact an...