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This paper presents a systematic finite element (FE) based parametric study to quantify the buckling capacity of perforated cold-formed and hot-rolled steel module column. The effects of various key geometric parameters such as eccentricity (location of perforation/column length), shapes (viz. circular, square and hexagonal), sizes (width/diameter) and height (depth) of perforation; and cross-sectional thickness, on the buckling performance of cold-formed and hot-rolled steel stub columns, have been investigated. Based on the analysis, the reduction in column capacity is found to be maximum when the perforation is located at column mid-height, as anticipated. The perforation shapes under consideration have been found to have marginal impact on the buckling capacity of the module stub columns, although the reduction in column capacity is seen to be in the order – square > hexagon > circular perforated columns (having same perforation size). The critical buckling capacity of perforated module column is observed to be linearly decreasing as the perforation size ratio (perforation size/flat-element width) increases. However, for the same width of perforation, increasing the perforation height up to 2.5 times the perforation width, the change in column capacity is found to be negligible. Furthermore, the applicability of existing design for perforated columns has been assessed and found that, although most of the design equations generate conservative and reliable predictions both for cold-formed and hot-rolled steel, the design formulae which are based on effective width method are found to be more accurate as compared to those which are based on total area method. © 2020 Elsevier Ltd

Department of Civil & Infrastructure Engineering

World University root node

Journal of Constructional Steel Research

Effect of access openings on the buckling performance of square hollow section module stub columns

This paper presents a preliminary experimental and numerical investigations on the axial compressive capacity of cold-formed steel of square hollow section (SHS) stub columns having central circular perforations. The stub columns were prepared from commercially available structural tubular steel members - Tata Structura-YSt 310 manufactured by Tata Steel India. Stub columns having various diameter of perforation to flat web width ratios, d/w ~ 0.1 to 0.9, were considered. Finite element (FE) models were developed to determined ultimate capacities of perforated columns, which were not included in the experiment procedure, via carefully validated FE procedure, using commercial FE software Abaqus. Based on the study, a near non-linear drop in the ultimate load capacity of perforated columns as the perforation size increases was observed. Further, column capacities predicted by design code and proposed equations in the literatures are compared with the test and FE ultimate column capacities and found that most of the design equations provided overly conservative and highly scattered predictions. Copyright © 2018 by The Hong Kong Institute of Steel Construction.

Proceedings of the 9th International Conference on Advances in Steel Structures, ICASS 2018

Capacity of cold-formed steel hollow stub columns with central circular perforations

This paper presents an experimental investigation into the mechanical properties of YSt-310 cold-formed steel hollow sections, which is one of the most widely used structural steel in India, under steady state elevated temperatures ranging from approximately ambient to 800 °C. Elevated temperature stress–strain curves and reduction factors of key material parameters such as Young's modulus; yield stress; stresses corresponding to 0.5%, 1.5% and 2.0% strains; tensile strength and corresponding strain (%); fracture strain (%) and Ramberg-Osgood parameter are reported. Further, the reduction factors obtained from the current experimental programme are compared with predictions based on current fire design standards as well as those reported in literatures for cold-formed steel at elevated temperature. Statistical analysis was carried out to check the reliability of the elevated temperature reduction factors and it was found that the existing design rules are inaccurate and not applicable to cold-formed hollow steels at elevated temperature. A new set of fire design reduction factors are then proposed for cold-formed steels hollow sections based on lower bound values, considering both the current and previously reported experimental data. The newly proposed reduction factors are shown to offer improved mean (conservative) and reliable predictions and therefore recommended for inclusion in future revisions of fire design codes. © 2019

Mechanical properties of YSt-310 cold-formed steel hollow sections at elevated temperatures

In this paper, effect of thickness on the structural performance of concentrically loaded semi-elliptical lean duplex stainless steel (LDSS) hollow stub columns is presented via nonlinear finite element (FE) analysis by using ABAQUS. The modeling procedure has been validated against the LDSS stub column experimental results available in literature. The cross-sectional dimensions considered in this analysis conform to the commercially available semi-elliptical hollow sections from Ancofer Stahlhandel GMBH. Extensive parametric study was carried out to study the structural performance by varying the thickness from t = 5 to 14 mm. Based on the FE analyses, it has been found that, for the sections considered, a near linear increase (~+300%) in column resistance (Pu) is seen with increase (~+180%) in thickness from t = 5 to 14 mm. Further, an enhanced strain hardening effect on the load capacity can be observed for the thicker sections, i.e., t ≥ ~12.5 mm. © 2019, Springer Nature Singapore Pte Ltd.

Lecture Notes in Civil Engineering

Semi-elliptical ldss hollow stub columns under axial compression

This paper describes an experimental and numerical investigation on torsional behaviour of unperforated and perforated cold-formed steel hollow section members. The material characteristics and torsional performance of YSt-310 cold-formed steel square hollow section members (conforming to Indian Standard 4923), were initially studied, experimentally. Effects of size, number, and position of circular perforation on member torsional strength were investigated using validated finite element models, via Abaqus. Additionally, using the FE analysis results, design equations were proposed in Eurocode (EN), Direct Strength Method (DSM) and Deformation Based Method (DBM) formats; for unperforated square hollow section members. The approach is then extended for perforated cases, having circular single and double perforations, using suitable reduction factors, considering effects of both cross-sectional slenderness and perforation size. The proposed design equations were assessed through reliability analysis and were found to be safe for design of cold-formed square hollow sections under torsion. © 2019 Elsevier Ltd

Cold-formed steel square hollow members with circular perforations subjected to torsion

An experimental programme to study the residual mechanical strength of Tata Structura-YSt 310 cold-formed steel square and rectangular tubular sections (conforming to Indian Standard 4923) after being exposed to elevated temperature is described in this paper. First, the coupon specimens extracted from the flat regions are exposed to pre-determined elevated temperature in the range ~ 300–800 °C, and then the residual mechanical properties and hardness value were estimated at ambient temperature after natural air cooling. The results from the experimental programme are reported in this paper in the form of post-firestress-strain curves and associated basic material properties (e.g. elastic modulus, proof stresses, tensile strength, percentage elongation at fracture, Ramberg-Osgood material parameters etc.) as well as surface hardness values. The test results showed that most post-fire mechanical properties are appreciably different from ambient temperature material properties when exposed to a temperature higher than ~400 °C; whilst elastic modulus appears to remain unaffected even when the exposed temperature is up to ~800 °C. A near linear relationship of post-fire material strengths and hardness value was observed. Two sets empirical equations are proposed separately to predict the residual post-fire reduction factors based on the i)current experimental results of Tata Structura-YSt 310 cold-formed steel, and ii) cold-formed steel of various grades presently available in the literatures. © 2018 Elsevier Ltd

Post-fire mechanical properties of YSt-310 cold-formed steel tubular sections

This paper describes an experimental study to estimate the stub columns capacity of cold–formed square (SHS) and rectangular hollow sections (RHS) containing two opposite central circular perforations at column mid–height. The stub columns were extracted from commercially available Tata Structura–YSt 310 tubular sections, with minimum yield strength of 310 MPa, conforming to Indian Standard 4923. The influence of two opposite central circular perforations on the structural performance of tubular steel stub columns under concentric loading was investigated for perforation size to flat width ratios up to 0.9 The local geometric imperfections, load–end shortening curves, strain distributions at mid height of column and typical failure modes observed from the present test programme are documented in this paper. Further, the ultimate column capacities recorded from the test programme are compared with codified design predictions as well as design equations proposed by various researchers. Based on the comparison, it is observed that the predictions made by most of the currently available design equations are conservative and reliable but generally scattered for design of cold–formed tubular structural steel stub columns having central circular perforations. © 2018 Elsevier Ltd

Thin-Walled Structures

Experimental investigation on performance of perforated cold–formed steel tubular stub columns

This paper describes experimental and numerical investigations conducted to characterize the basic material properties and design of YSt–310 cold–formed structural steel sections at Indian Institute of Technology, Guwahati. Square (SHS) and rectangular (RHS) hollow sections with minimum yield strength of 310 MPa manufactured by Tata Steel India, were considered in the study. Initially, results from elemental analysis via optical emission spectrometer (OES) investigation and metallographic examination using optical microscope are presented. Key stress–strain parameters viz., Young's modulus, proof stress, ultimate strength, percentage elongation, strain hardening exponent etc. were generated based on flat, corner and weld coupon tests data. Extent of corner strength enhancement due to cold – forming determined using Vickers's microhardness test are reported. Additionally, cross – section capacity of the stub columns were also investigated experimentally and numerically. The column capacities generated from test and finite element study are compared with the existing design code – EN 1993–1–1 (EN 1993-1-1, 2005) [1] and design rules – continuous strength method (CSM) (Zhao et al., 2017) [2] and direct strength method (DSM) (North American Specifification for the Design of Cold-Formed Steel Structural Members, 2016; Arrayago et al., 2017) [3,4]. Based on the comparison, modifications on the existing design code and rules are suggested to provide a more accurate and reliable compressive design prediction. © 2017 Elsevier Ltd