Teoman Peköz

Computational modeling of cold-formed steel: characterizing geometric imperfections and residual stresses

Thin-walled, cold-formed steel members exhibit a complicated post-buckling regime that is difficult to predict. Today, advanced computational modeling supplements experimental investigation. Accuracy of computational models relies significantly on the characterization of selected inputs. No consensus exists on distributions or magnitudes to be used for modeling geometric imperfections and for modeling residual stresses of cold-formed steel members. In order to provide additional information existing data is collected and analyzed and new experiments performed. Simple rules of thumb and probabilistic concepts are advanced for characterization of both quantities. The importance of the modeling assumptions are shown in the examples. The ideas are summarized in a preliminary set of guidelines for computational modeling of imperfections and residual stresses.

The finite element method for thin-walled members-applications

Traditionally numerous physical tests have been required to develop and verify newly proposed design procedures. The availability of powerful computers and software makes the finite element method an essential tool in such research. Analysis types, material models, elements and initial conditions that are taken into account in the finite element analysis of thin-walled structures are discussed. A list of programs developed in recent studies and example problems of the finite element method application to thin-walled structures are given.

The finite element method for thin-walled members—basic principles

The application of the finite element method to thin-walled structures often requires non-linear analysis. Whereas in linear finite element analyses errors are easily made, this is even more so in the non-linear analyses. This paper focuses on possible sources of error in linear and non-linear finite element solutions, and gives suggestions how to check and prevent these errors.

Torsion in thin-walled cold-formed steel beams

Thin-walled cold-formed steel members have wide applications in building structures. They can be used as individual structural framing members or as panels and decks. In general, cold-formed steel beams have open sections where centroid and shear center do not coincide. When a transverse load is applied away from the shear center it causes torque. Because of the open nature of the sections, torsion induces warping in the beam. This paper summarizes the research on the behavior of cold-formed steel beams subject to torsion and bending. The attention is focused on beams subject to torque, because of the effect of transverse loads not applied at the shear center. A simple geometric nonlinear analysis method, based on satisfying equilibrium in the deformed configuration, is examined and used to predict the behavior of the beams. Simple geometric analyses, finite element analyses and finite strip analyses are performed and compared with experimental results. The influence of typical support conditions is studied and they are found to produce partial warping restraint at the ends. This effect is accounted for by introducing hypothetical springs. The magnitude of the spring stiffness is assessed for commonly used connections. Other factors that affect the behavior of cold-formed steel members, such as local buckling, are also studied.

A Probabilistic Examination of the Ultimate Strength of Cold-formed Steel Elements

The statistical characteristics (mean and variance) of the ultimate strength of cold-formed steel plates in uniform compression and pure bending are calculated and compared to deterministic approximations. Three quantities: plate thickness, longitudinal flexural residual stress magnitude and first mode imperfection magnitude, are treated as random variables. Based on existing experimental data, appropriate probability distributions are determined for the three random variables. The ultimate strength calculations are performed numerically using the finite element method (FEM). The statistical characteristics are calculated using two methods: Monte Carlo simulation and Taylor series approximation. The results are compared to the deterministic design approach of the American Iron and Steel Institute (AISI) Specification for the design of cold-formed structural members.

The behavior and design of longitudinally stiffened thin-walled compression elements

Abstract The behavior and design of cold-formed steel sections with single and multiple intermediate stiffeners in the compression, flange is investigated. Existing experimental data are used to evaluate critically the AISI specification and Eurocode. For bending strength prediction of sections with multiple intermediate stiffeners, the AISI specification can be quite unconservative and Eurocode often Yields overly conservative results. Existing experimental data are used to calibrate a finite element model. An extensive parametric study is conducted using the finite element model. The results of the study are used to gain a better understanding of the behavior of these elements, and to help evaluate alternatives to the existing design procedures. Based on the existing data and the finite element stud two alternatives to the existing strength prediction procedures are advanced.

Bending strength of standing seam roof panels

Abstract The standing seam roof panel system is used extensively in residential, commercial and institution type building structures in the USA. The roof system is typically, designed for both gravity loading (construction and other live load) and uplift (from wind). Under gravity load, the outstanding leg of the connected panels may be subject to distortional buckling-lateral displacement of the unsupported compression flange with rotation about the web-tension. flange juncture. In this paper, experimental results from tests on four full-scale panel systems are presented and an analytical procedure is recommended for estimating the distortional buckling capacity of the standing seam roof system. Using a simplified design method for inelastic behavior, relatively accurate estimates of the maximum capacity for a system under gravity, load are computed.