Virtual testing against experiment for post-buckling behaviour of coldformed steel columns

Cold-formed steel has already started to replace hot rolled companions in some structural applications. Advantages of cold-formed steel originate from its high strength over weight ratio and ease of manufacturing and construction compared to hot rolled heavy sections. Moreover, cold-formed columns have significant post-buckling reserve which has the potential to be exploited in design process. Therefore, it is essential to predict the response of cold-formed columns by means of high fidelity engineering techniques. Herein an in depth study which links experimental testing and non-linear computational capabilities is undertaken to address the failure behaviour of cold-formed columns. Experimental program comprises coupon tests to specify material properties and compression testing of fixed end cold-formed columns. Thereafter, measured material properties are utilized to generate a stress-strain curve for finite element models. Boundary conditions imposed into simulation models in such a way that would represent test conditions. Creating a suitable mesh for different cross sectional dimensions, different shapes of initial imperfections are introduced into models to compare contributions to performance of columns. Predicted collapse loads and modes via finite element models are assessed against test results. Mesh and initial imperfection sensitivities on failure characteristics are discussed. Finally a general assessment is made for the deployed testing and simulation to generate knowledge for the design evaluation of cold-formed steel columns. Key findings and discussions of present study have the potential to lead to develop promising cold-formed steel column virtual test models

Tailoring Compression Performance of Cold-Formed Steel Columns

Since thin-walled structural analysis and design procedures are utilized for cold-formed steel columns, it is first necessary to understand thin plate behavior to employ proper cross sections which will serve under compression actions. As is well known, thin plates without any longitudinally and/or laterally stiffening elements usually are not present in structural applications. These stiffening elements significantly improve local buckling and collapse characteristics of plates, providing optimized solutions in terms of strength and cost. In cold-formed steel industry there exist some tailoring methods for columns to use the cross-section material more effectively. Designing lipped channels instead of plain ones or deploying rack sections can be shown as examples of stiffening and enhancing flange compression performance. Present study offers a novel tailoring technique which has the potential to improve collapse performance of cold-formed steel columns. Considering the manner of stiffening for thin plates, present work assesses cold-formed steel columns which are manufactured using stiffened sheets. Used stiffened sheets are called as checkered sheets which contain small stiffeners on thin plates in a shape of diamond pattern and are generally used to cover stairs and decks in outdoor environments to prevent slip. Aiming at investigating contributions of small stiffeners on compression performance of cold-formed steel columns, an experimental study was undertaken and column specimens were tested to failure. Plain channel test specimens were manufactured using press braking method and boundary conditions of specimens were designed in such a way that would represent fixed ends. Accompanying the experimental program, non-linear finite element simulation works and AISI-2007 method were employed for manufactured columns using equivalent thickness approach. Results imply that with the proper geometrical configurations, reserve of cold-formed steel columns manufactured using checkered sheets offer structural efficiency in satisfying greater compression loadings compared to that of columns manufactured using plain sheets of equivalent thickness. This stiffened sheets concept has the potential to be facilitated in cold-formed steel commercial and residential structures. More efficient sections also can be acquired for design purposes by optimizing those stiffener configurations under compression loadings

Flexural behavior of concrete beams reinforced with different types of fibers

Enhanced tensile properties of fiber reinforced concrete make it suitable for strengthening of reinforced concrete elements due to their superior corrosion resistance and high tensile strength properties. Recently, the use of fibers as strengthening material has increased motivating the development of numerical tools for the design of this type of intervention technique. This paper presents numerical analysis results carried out on a set of concrete beams reinforced with short fibers. To this purpose, a database of experimental results was collected from an available literature. A reliable and simple three-dimensional Finite Element (FE) model was defined. The linear and nonlinear behavior of all materials was adequately modeled by employing appropriate constitutive laws in the numerical simulations. To simulate the fiber reinforced concrete cracking tensile behavior an approach grounded on the solid basis of micromechanics was used. The results reveal that the developed models can accurately capture the performance and predict the load-carrying capacity of such reinforced concrete members. Furthermore, a parametric study is conducted using the validated models to investigate the effect of fiber material type, fiber volume fraction, and concrete compressive strength on the performance of concrete beams

Impact of finite element idealisation on the prediction of welded fuselage stiffened panel buckling

Lap joints are widely used in the manufacture of stiffened panels and influence local panel sub-component stability, defining buckling unit dimensions and boundary conditions. Using the finite element method it is possible to model joints in great detail and predict panel buckling behaviour with accuracy. However, when modelling large panel structures such detailed analysis becomes computationally expensive. Moreover, the impact of local behaviour on global panel performance may reduce as the scale of the modelled structure increases. Thus this study presents coupled computational and experimental analyses, aimed at developing relationships between modelling fidelity and the size of the modelled structure, when the global static load to cause initial buckling is the required analysis output. Small, medium and large specimens representing welded lap-joined fuselage panel structure are examined. Two element types, shell and solid-shell, are employed to model each specimen, highlighting the impact of idealisation on the prediction of welded stiffened panel initial skin buckling. </jats:p

Tailoring Static Strength Performance of Metallic Stiffened Panels by Selective Local Sub-Stiffening

Today's high-strength and damage tolerant materials allow for significant increases in aluminum working and limit stresses. To fully exploit material improvements as weight savings on aircraft primary structures, it is desirable to enhance the buckling stability of stiffened panels. The work presented in this paper proposes that with the introduction of selective local sub-stiffening, local bucking and panel collapse behavior may be effectively tailored without increased material volume. This would enable greater panel working stresses, translating increases in strength characteristics of new materials into appropriate structural weight savings. Additionally, considering the issues surrounding the damage tolerance of integrally stiffened panels, local sub-stiffeners may be designed to act as integrated crack retarders, improving the damage tolerance characteristics of the structure. This paper presents the experimental and computational design, analysis and optimization work undertaken in assessing and validating the use of selective local sub-stiffening. The experimental work has demonstrated potential combined performance gains for both local plate buckling and panel post-buckling collapse of the order of 10% and 12% respectively. The analysis work undertaken has enabled the development of simple design guidelines for sub-stiffening and potential analysis and optimization techniques for the combined panel configuration and local sub-stiffener design.</p