Cao Hung Pham

Direct Strength Design of Cold-Formed C-Sections for Shear and Combined Actions

In order to extend the Direct Strength Method (DSM) of design of cold-formed sections to shear, and combined bending and shear, a research program has been performed recently at the University of Sydney. This includes evaluation and calibration of DSM design rules for shear and combined actions when applied to an extensive series of purlins tested at the University of Sydney, as well as shear only and combined bending and shear tests on channel sections. The paper summarises this research, as well as making proposals for shear, and combined actions. Two features researched are the effect of full section shear buckling (as opposed to web only shear buckling), and tension field action. Full section buckling is a feature of the DSM but requires software that can evaluate full sections for shear. Methods for doing this are summarised in the paper.

Experimental Investigation of High Strength Cold-Formed C-Sections in Combined Bending and Shear

In roof systems, a high strength steel profiled sheeting fastened to high strength steel cold-formed purlins of a lipped C- or Z-section is commonly used throughout the world. The design of such systems is performed according to the provisions of the limit states Australia/New Zealand Standard for Cold-Formed Steel Structures in Australia and the North American Specification for the Design of Cold-Formed Steel Structural Members in the United States. In both standards, which include the newly developed direct strength method of design (DSM), the method presented is limited to pure compression and pure bending. The situations of pure shear and combined bending and shear as occurs in a continuous purlin system are not considered. In order to extend the DSM to purlin systems, three different test series on high strength cold-formed C-section purlins have been performed at the University of Sydney. The test series include predominantly shear, combined bending and shear, and bending only test series. Two different section depths and three different thicknesses of the lipped channel section were tested in this study. Further, tests with and without torsion/distortion restraint straps screwed on the top flanges adjacent to the loading points were also considered. This paper summarizes the test results and formulas developed from the effective width method and the DSM. Proposals for design are included in this paper. Comparisons with the Australian Steel Structures Standard are also included to take account of the tension field action.

Experimental Investigation and Direct Strength Design of High-Strength, Complex C-Sections in Pure Bending

AbstractPlain C- or Z-sections are two of the most common cold-formed steel shapes in use throughout the world. Other shapes are high-strength SupaCee and SupaZed (Bluescope Steel Ltd., Melbourne, Australia) steel sections, which are widely used in Australia as purlins in roof and wall systems. They contain additional return lips and web stiffeners that enhance the bending capacity of the sections. Design methods for these sections are normally specified in the Australian/New Zealand Standard for cold-formed steel structures or the North American Specification for cold-formed steel structural members. In both standards, which include the newly developed direct strength method of design (DSM), the method presented is developed for beams and columns, including the reliability of the method. This paper presents two different test series on both plain C- and SupaCee sections in pure bending (constant moment). They were performed at the University of Sydney for the extension of the DSM to include channel secti...

Direct Strength Method of Design for Channel Sections in Shear with Square and Circular Web Holes

AbstractThe direct strength method (DSM) design rules for cold-formed steel members in shear have been incorporated recently into the North American specification for the design of cold-formed stee...

Experimental Study of Longitudinally Stiffened Web Channels Subjected to Combined Bending and Shear

AbstractThe direct strength method (DSM) of design of cold-formed sections has been recently extended in the North American Specification for Cold-Formed Steel Structural Members NAS S100:2012 to include shear. The two new features of the DSM rules for shear researched are the effect of full-section shear buckling as opposed to web-only shear buckling and tension field action (TFA). The prequalified sections in the rules include sections with flat webs and webs with small intermediate longitudinal stiffeners. In order to extend the range to larger intermediate stiffeners as occurs in practice, a series of fourteen shear tests have been performed at the University of Sydney for C-sections with rectangular stiffeners of varying sizes. Six different types of stiffeners were tested with an additional preferred plain section. Each type of section was tested twice to ensure accuracy. As the web stiffener sizes increase, the shear buckling and strength of the sections are expected to improve accordingly. However...

Failure Analysis of a Cold-Rolled Steel Tensile Specimen Using a Damage-Plasticity Model

This paper presents preliminary results on the formulation of a damage-plasticity model and its applications for the failure analysis of cold-rolled high strength steels. The model is based on von Mises plastic theory combined with a damage criterion to capture both hardening and softening responses. The proposed constitutive model is calibrated against available experimental data and implemented into the ABAQUS finite element (FE) package for the failure analysis in a tensile test of cold-formed steel (CFS). Both the experimental overall response of the member and its fracture pattern can be predicted, showing the potentials of the model in structural applications. In addition, both advantages and disadvantages of the model are discussed with proposals for further improvements.

Image Processing in the Characterization of Crack Propagation in Cold-Formed Steel Samples

This paper focuses on a technique developed to monitor and track automatically the crack propagation at two sides of the corner of a coupon to investigate the corner effect on the fracture toughness of the high strength cold-formed steel channel sections. The coupons taken longitudinally along the corners of channel sections were initially pre-cracked at both sides under fatigue loading and then loaded monotonically under tension until failure. When assessing the fracture toughness, it was particularly important to identify the precise moment of initiation and propagation of the pre-existing cracks. The technique was based on image processing with a grid of circular targets attached on the surface prior to the monotonic test and used for scaling and orientating all acquired images. A digital correlation procedure was applied to track both edges of the notch of each crack and quantify its opening during the test. By correlating the changes in the rate of crack mouth opening, the different stages of propagation could be identified together with the corresponding critical loads. The fracture toughness is determined based on these critical loads which could not be captured directly from the load versus axial displacement curves.

Effect of Manufacturing Process on Material Properties at the Corners of G450 Cold-Formed Steel Channel Sections

The use of cold-formed steel structures in the construction industry has become widely popular over the past decade. This has led to the necessary understanding of the effects of cold-working process on cold-formed steel members. The manufacturing process of cold-formed steels starts with cold-rolling the hot-rolled steel sheet under a series of rollers until a thickness is achieved. The process is followed by cold-bending to create cold-formed sections with desired shapes at ambient temperature. The plastic deformation associated with the rolling and bending processes results in strain hardening of the material and this in turn affects the properties. This paper presents both microstructural and micromechanical investigations on the blank and bent areas of 3.0 mm thick C-shaped cold-formed sections. Vickers hardness tests show a hardness increase at the bent areas. The observation of the bent region using scanning electron microscopy (SEM) reveals changes in the grain structures. Additionally, electron backscatter diffraction (EBSD) measurements have been conducted for an in-depth characterization. Understanding the changes in the microstructure of the material will provide insight on the mechanical behavior of these members.

Numerical Simulations of Cold-Rolled Aluminium Alloy 5052 Channel Sections in Stub Column Tests

The paper describes finite element analyses using the program ABAQUS 6.14 of cold-rolled alluminium alloy 5052 channel sections in stub column tests. Aluminium structural members have been used considerably in not only roof systems but also primary load-bearing components due to such advantages as superior corrosion resistance, light weight, ease of maintenance, constructability and recyclability. While the majority of aluminum structural applications are formed by extrusion, recently, aluminum Z- and C- sections have been successfully cold-formed from aluminium coil using existing rollers for cold-formed steel sections. The results of nonlinear analysis by the finite element method (FEM) depend on the measured input parameters such as the material properties, actual initial geometric imperfections and forming-induced residual stresses. The paper summaries the results of the finite element nonlinear simulations of the stub column tests on channel sections performed at the University of Sydney. The FEM results are compared and calibrated against the tests. The effect of the measured input parameters is also discussed thoroughly.

Application of the THIN-WALL-2 V2.0 Program for Analysis of Thin-Walled Sections Under Localised Loading

The Finite Strip Method (FSM) has been developed for pre-buckling and buckling analyses of thin-walled sections under localised loading for general end boundary conditions. The theory is included in the THIN-WALL-2 V2.0 program which has been developed at the University of Sydney using a MATLAB graphical interface, Visual Studio C++ computational engines and a FSM module. The paper describes the application of the THIN-WALL-2 V2.0 program in analysis of thin-walled sections under the four localised loading cases namely IOF (Interior one-flange loading), EOF (End one-flange loading), ITF (Interior two-flange loading) and ETF (End two-flange loading). A linear analysis is required for pre-buckling analysis to determine the pre-buckling modes and the membrane stresses of structural members subjected to localised loading. These stresses are then used in the buckling analysis to get the buckling load and the buckling modes of the structural members.