No. R825, January, 2003
Yang, D and Hancock, GJ
Compression Tests of Cold-Reduced High Strength Steel Channel Columns failing in the Distortional Mode
Full Report in PDF
Abstract
This report describes a series of compression tests performed on lipped channel section columns fabricated from cold-reduced high strength steel of thickness 0.42 mm with nominal yield stress 550 MPa. The test results presented in the paper are the third stage of an Australia Research Council research project entitled “Compression Stability of High Strength Steel Sections with Low Strain-Hardening”. A range of lengths of lipped channels with intermediate stiffeners in the web and the flanges were tested between fixed ends to determine the strength of the sections.
For the lipped channel sections, the failure resulted from local and distortional buckling with interaction between the modes. The tests indicated that distortional buckling and the interaction of local and distortional buckling may have a significant effect on the strength of the sections formed from such thin steel.
The report presents the results obtained experimentally and theoretically using the effective width method and the direct strength method. Two new design methods are proposed to account for the adverse interaction of local and distortional buckling.
Keywords
Cold reduced; High strength steel; Lipped-channel section; Local buckling; Distortional buckling
No. R826, March, 2003
Rasmussen KJR, Burns, T and Bezkorovainy
Design of Stiffened Elements in Cold-formed Stainless Steel Sections
Full Report in PDF
Abstract
This report presents strength equations for single stainless steel stiffened elements applicable to the range of alloys included in the Australian, American and European standards for stainless steel structures. Cold-formed sections with stiffened elements are considered and the enhanced mechanical properties of the corners are taken into account to show that the Winter equation may or may not conservatively predict the strength, depending on the corner area relative to the area of the flat part. The report shows that the Winter equation may be used safely for the design of stiffened elements provided half of the area of the adjacent corners exceeds 10-15% of the flat area, depending on the alloy and whether the section is cold-rolled or brake-pressed. An equation is derived for determining the reduction factor to be applied to the Winter strength when the minimum corner area requirement is not met. The reduction factor is less than 10% for practical sections.
Keywords
Stainless steel, local buckling, stiffened elements, cold-formed sections, design
No. R827, March, 2003
Wheeler, A, Clarke, M and Hancock, GJ
Design Model for Bolted Moment End Plate Connections Joining Rectangular Hollow Sections Using Eight Bolts
Full Report in PDF
Abstract
In this report a model for the determination of the serviceability and ultimate moment capacities of bolted moment end plate connections utilising rectangular hollow sections joined with eight bolts is presented. The connection configuration is such that two bolts are located above each of the flanges and beside each of the webs. The model considers the combined effects of prying action due to flexible end plates, the formation of yield lines in the end plates, and failures due to punching shear and beam section failure. The model is calibrated and validated using experimental data from a test program.
The design model constitutes a relatively simple method for predicting the serviceability and ultimate moment capacities for the particular type of bolted moment end plate connection described herein.
Keywords
Tubular, connections, moment end plate, structural design, yield line, prying
No. R828, June, 2003
Trahair, NS
Non-Linear Elastic Non-Uniform Torsion
Full Report in PDF
Abstract
This paper is concerned with large twist rotations of elastic thin-walled open section beams which induce additional longitudinal stresses which exert non-linear “Wagner” stiffening torques.
The non-linear behaviour of a narrow rectangular beam is first analysed and then this is extended to elastic beams of general cross-section. Expressions are derived for the non-linear “Wagner” section constants for narrow rectangular sections, doubly symmetric I-sections, and mono-symmetric equal angle sections.
A general finite element method of analyzing non-linear torsion is described, and used to develop a computer program FENLT. This program can analyse a beam of general cross-section under any combination of concentrated and distributed torques and concentrated bimoments, and which may be prevented from twisting or warping at points along its length. The program is validated by comparison with closed form or numerical solutions for a number of simple examples.
Keywords
Elasticity, non-linear, non-uniform, open sections, thin-walled, torsion, twist, warping.
No. R829, May, 2003
Rondal, J and Rasmussen, KJR
On the Strength of Cast Iron Columns
Full Report in PDF
Abstract
The aim of the report is to show that modern methods of verification of steel structures can be used for the structural appraisal of old cast-iron columns. The proposed method of verification takes account of the geometrical imperfections which are typical for cast-iron columns and of the particular behaviour of the material which is distinct from modern structural steel in that the tension strength is significant lower than the compression strength, the stress-strain curve is non-linear rather than bi-linear and the Young’s modulus is about 2/5 the value for modern steels. The report proposes equations for calculating the strength of cast iron columns by checking failure by yielding in compression and fracture in tension. The proposed strength equations are compared with experimental results obtained by Hodgkinson (1840) and Tetmayer (1901).
Keywords
Cast iron, columns, buckling, historical buildings, design, imperfections, nonlinear material
No. R830, June, 2003
Rasmussen, KJR
Design of Angle Columns with Locally Unstable Legs
Full Report in PDF
Abstract
The report is concerned with angle section columns whose legs are slender and thus subject to local buckling in their ultimate limit state. For such slender angle sections, the local buckling mode is identical to the torsional mode and traditional design procedures become excessively conservative because they account for the torsional (local) buckling mode twice. The report describes design methods for slender equal angles which ignore torsion in determining the overall buckling stress and uses recently presented effective width equations to accurately determining the bending capacity of angle sections, as required in the beam-column design approach. The shift in the effective centroid resulting from local buckling is determined from the actual stress distribution, as obtained using Stowell’s classical solution, rather than the effective cross-section. Having validated the design procedure against tests on slender equal angles, the same procedure is applied to slender unequal angles. The columns are assumed to be simply supported and thus allowed to rotate about their principal axes.
Keywords
Angles, columns, beam-columns, local buckling, flexural buckling, flexural-torsional buckling, design, shift of the effective centroid.
No. R831, August, 2003
Teh, LH and Rasmussen, KJR
Strength of Welded T-Joint Truss Connections between Equal Width Cold-Formed RHS
Full Report in PDF
Abstract
The report describes laboratory tests of arc welded T-joints between equal width rectangular hollow sections. The brace and chord members were cold formed with a nominal yield stress of 350 MPa. The welds were laid using MMAW and GMAW processes without profiling the brace ends. The brace of each specimen was loaded in tension to failure with the chord supported continuously so as not to induce significant bending effects.
The test results showed that the joint strength can be improved by using backing strips for the butt welds, while backing rods (or filler rods) should not be used as they led to larger variation in joint strengths, and often, inferior strengths. The test strengths are compared with the design strengths obtained using the IIW Recommendations and Eurocode3, Part 1.8. It is shown that for cold-formed tubes with a nominal yield stress of 350 MPa (or above), a design check on the strength of the butt (or groove) weld is required in addition to the checks on the strengths of the chord and brace members specified in the current design guidelines. An equation is proposed for calculating the strength of the weld.
Keywords
Butt weld, brace-to-chord connection, cold-formed steel, metal arc welding, rectangular hollow section, T-joint design
No. R832, September, 2003
Teh, LH and Hancock, GJ
Improving Rotation Capacities of Stiffened Welded Knee Joints between DuraGal C450 RHS
Full Report in PDF
Abstract
This report describes a new welding-based solution that significantly increases the rotation capacity of a stiffened welded knee joint between DuraGal C450 RHS under opening moment. The proposed solution is more economical than the use of internal sleeves, and can be applied to new as well as existing structures. The solution involves the use of extra layers of weld on the inner (tension) flange of a stiffened welded knee joint. Laboratory test results are presented to demonstrate that the solution enables such a joint between DuraGal C450 150x50x4 or 150x50x5 RHS to satisfy the rotation capacity requirement specified for plastic design of steel frames. A number of factors that may contribute to the lack of rotation capacity of a normally welded stiffened knee joint are discussed. The reasons why the new solution results in increased rotation capacities are explained in terms of strain redistribution and strain reduction in the tensile regions around the knee joints. It is shown through experimental tests and finite element analyses that the most important parameter of the proposed solution is the width of the extra layers of weld. Although the presence of the seam weld in the inner flange results in a significantly reduced rotation capacity, the proposed solution still ensures an adequate rotation capacity for a stiffened welded knee joint between DuraGal 150x50x5RHS. This report also discusses an appropriate definition for the rotation capacity of a knee joint under opening moment, including the plastic moment to be used in measuring the rotation capacity.
Keywords
Cold-formed steel, ductility, hollow sections, plastic design, rotation capacity, welded joints
No. R833, October, 2003
Trahair, NS
Buckling and Torsion of Steel Angle Section Beams
Full Report in PDF
Abstract
Although steel single angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion, their behaviour may be extremely complicated, and the accurate prediction of their strengths very difficult. Further, many design codes do not have any design rules for torsion, while some recommendations are unnecessarily conservative, or are of limited application, or fail to consider some effects which are thought to be important.
This paper is one of a series on the behaviour and design of single angle section steel beams. Two previous papers have studied the biaxial bending behaviour of restrained beams, a third has studied the lateral buckling of unrestrained beams, and a fourth the biaxial bending of unrestrained beams. In each paper, simple design methods have been developed.
In this present paper, an approximate method of predicting the second-order deflections and twist rotations of steel angle section beams under major axis bending and torsion is developed. This method is then used to determine the approximate maximum biaxial bending moments in such beams, which are then used with the section moment capacity proposals of the first paper of the series and the lateral buckling proposals of the third paper to approximate the member capacities.
Keywords
Angles, beams, bending, buckling, design, elasticity, member capacity, moments, section capacity, steel, torsion.