This paper discusses the issues involved in using simplified second‐order inelastic analysis for design of steel‐frame structures. In particular the elastic‐plastic hinge method is examined and the assumptions inherent in its use are outlined. It is shown that this method does not always lead to an accurate representation of inelastic behavior, and that it does not furnish enough information for assessment of the ultimate strength of individual members. An alternative approach called the refined plastic‐hinge method is introduced, and its design implications are discussed. The refined plastic‐hinge approach accounts for inelastic stiffness degradation, and a column tangent‐modulus expression is utilized to represent the effective stiffness of the element when it is loaded with large axial loads. This paper highlights and illustrates the qualities and limitations of these two inelastic analysis methods with regard to their acceptability for use in predicting the ultimate strengths of steel frames and their...

Second‐Order Refined Plastic‐Hinge Analysis for Frame Design. Part II

The main objective of this paper is to provide an efficient and accurate finite element model to understand the behavior of cold-formed steel plain angle columns. The effects of initial local and overall geometric imperfections have been taken into consideration in the analysis. The material nonlinearities of flat and corner portions of the angle sections were incorporated in the model. Failure loads and buckling modes as well as load-shortening curves of plain angle columns were investigated in this study. Furthermore, the residual stresses of a column test specimen were measured and plotted. The effect of residual stresses on the buckling behavior was studied using the finite element model. The nonlinear finite element model was verified against experimental results. The finite element analysis was performed on plain angles compressed between fixed ends over different column lengths, and column curves were obtained. An extensive parametric study was carried out using the finite element model to study the effects of cross-section geometries on the strength and behavior of angle columns. The column strengths predicted from the finite element model were compared with the design strengths calculated using the American Specification and Australian/New Zealand Standard for cold-formed steel structures. In addition, the results obtained from the finite element model were also compared with the design strengths obtained from the design rules proposed by other researchers.

Behavior of Cold-Formed Steel Plain Angle Columns

Optimal design of Schwedler and ribbed domes via hybrid Big Bang–Big Crunch algorithm

Behavior of short circular tubed-reinforced-concrete columns subjected to eccentric compression

Dome structures provide cost-effective solutions for covering large areas without intermediate supports. In this article, simple procedures are developed to reach the configuration of the geodesic domes. A new definition of dome optimization problems is given which consists of finding optimal sections for elements (size optimization), optimal height for the crown (geometry optimization) and the optimum number of elements (topology optimization) under determined loading conditions. In order to find the optimum design, the recently developed meta-heuristic algorithm, known as the Charged System Search (CSS), is applied to the optimum design of geodesic domes. The CSS takes into account the nonlinear response of the domes. Using CSS, the optimum design of the geodesic domes is efficiently performed.

Geometry and topology optimization of geodesic domes using charged system search

Members carrying both axial force and bending moment are subjected to an interaction between these effects. The analysis of a beam-column using stability functions as an alternative to the stress stiffness matrix is discussed. Explicit expressions for stability functions for three-dimensional beam-columns, in terms of member length, cross-sectional properties, axial force, and the end moments, are derived. The effect of flexure on axial stiffness and the effect of axial force on flexural stiffness and stiffness against translation are considered in the derivation of stability functions. The effect of axial force on torsional stiffness and the effect of torsional moment on axial stiffness are neglected. The nonlinear stiffness matrix of a three-dimensional beam-column using the stability functions is presented by modifying the linear elastic stiffness matrix for a beam-column (which includes the effect of shear deformations) available in the literature. A numerical example showing the calculation of stability functions for a given beam-column is also presented.

Stability Functions for Three‐Dimensional Beam‐Columns

Structural steel angles have a wide variety of applications. However, steel angles have not received the attention comparable to heavy shapes such as wide flange sections. For steel angles, flexural buckling strength is the basic design strength, while the torsional-flexural buckling strength is computed in many codes by modifying the design procedure for flexural buckling strength. This paper presents the results of an experimental investigation of 26 hot-rolled steel angles under concentric axial compression failing in flexural buckling. The width-thickness ratios of test specimens ranged from 6 to 16. The slenderness ratios varied from 68 to 188, covering almost the entire practical range. Residual stresses and yield stresses across the cross sections were determined and initial out-of-straightness was measured. These data were used in the development of a column curve reported in a companion paper.

Flexural Buckling of Steel Angles: Experimental Investigation

Evaluation of non-linear analysis of guyed antenna towers

Dynamic response of guyed masts

Structural steel angles have a wide range of applications requiring a comprehensive design methodology. One of the most important aspects of steel-angle design is the flexural buckling strength. In this paper, the test data for flexural buckling reported in a companion paper as well as in published investigations are compared with current specifications, and the need for the development of a separate column curve for hot-rolled steel angles is established. The experimental data consist of 71 compression tests from five different studies and residual stress and out-of-straightness measurements. A finite-element analysis and a maximum strength analysis have been carried out using the available test data. Nine column curves have been generated. The average curve lies between the Structural Stability Research Council (SSRC) curves 1P and 2P. Equations for the curve have been presented. This column curve can be adopted for routine design or may be used to calibrate special code clauses.

Murty K. S. Madugula

Papers

Stability Functions for Three‐Dimensional Beam‐Columns

Flexural Buckling of Steel Angles: Experimental Investigation

Evaluation of non-linear analysis of guyed antenna towers

Dynamic response of guyed masts

Development of Column Curve for Steel Angles