https://pureadmin.qub.ac.uk/ws/files/16135230/Optimal_design_of_long_span_steel_portal_frames_using_fabricated_beams.pdf

Optimal design of long-span steel portal frames using fabricated beams

In this work, non-uniform steel members with or without initial geometrical or loading imperfections, that are loaded by axial forces applied concentrically or eccentrically and by concentrated moments applied at the ends or at intermediate points, are studied. More specifically, steel members with varying cross-sections, tapered or stepped or members consisting by two different tapered parts are considered. The formulation presented in this work is based on solving the governing equation of the problem through a numerical method where the eigenshapes of the member are employed. A failure plasticity criterion is introduced for members especially the short ones that will never reach the elastic critical buckling load. Although only the simply supported beam-column case is studied herein, it is obvious that the method can be extended to multi-span beams and frames, by employing the corresponding eigenshapes. Useful diagrams are presented for both the critical buckling loads and the equilibrium paths showing the influence of the main characteristics of the beam-column. non-uniform steel members with or without imperfections (of any form), loaded by axial forces (concentrically or eccentrically applied) and by concentrated moments applied at its ends or intermediate points are studied. The steel members with cross-section that may vary along the length, can be tapered or stepped or they can be members consisting by two unequal tapered parts. The imperfections considered may have any form. The formulation presented in this paper is based on solving the governing equation of the problem through the Galerkin method using the eigenshapes of the member. A plasticity failure criterion is introduced for stub or short members that will never reach the elastic critical buckling load. Although in this paper only the simply supported single-span beam-column is studied, it is obvious that the formulation presented may be extended to any type of frame members or frames using the corresponding eigenshapes. The results are presented in the form of diagrams either for the critical buckling loads or for the equilibrium paths, showing the influence of the main member's characteristics, as for example the cross-sectional variation law, the interme- diate loads and bending moments or the existing imperfec- tions on the above mentioned buckling loads and equilibrium paths. Although these diagrams are derived for a simply sup- ported beam-column they can be readily employed for the design of steel frames with such members through the use of the equivalent buckling length factor concept.

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Stability of Steel Columns with Non-Uniform Cross-Sections

The purpose of this paper is to validate the General Method for the stability check of unrestrained I-section web-tapered columns in fire situation. The General Method (clause 6.3.4 of EN 1993-1-1) covers the safety check of structural elements with complex support conditions and/or of non-prismatic members. However, the fire part of the Eurocode 3 (EN 1993-1-2) gives no further indication regarding the applicability of the method at elevated temperatures, apart from adapting the methodology to fire using the reduction factors for steel material properties, which is identified as a gap in the current version of the norm. To ascertain the validity of said adaptations, the ultimate capacity of members at elevated temperature has been obtained numerically with GMNI-Analyses and a parametric investigation incorporating I-section web-tapered columns built from slender (class 4) cross-sections has been carried out, with special attention to the influence of local buckling on member stability. It has been demonstrated that a straightforward application of the temperature-reduced mechanical properties of steel in the General Method results in an unsafe methodology, therefore justifying improvements to the procedure. In this work, this is done by i) proposing a novel methodology for the calculation of the in-plane load amplifier α u l t , k and ii) recalibrating the EN 1993-1-2 buckling curve. Not only does this new procedure improve the accuracy of the methodology but it also foregoes the otherwise necessary evaluation of the critical cross-section along the column.

The General Method for the fire design of slender I-section web-tapered columns

Low-rise metal buildings constitute a large portion of the nonresidential construction in the United States These buildings are, in most cases, characterized by a pinned column-to-foundati

Reversed Cyclic Behavior of Column-to-Foundation Connections in Low-Rise Metal Buildings

This paper proposes a novel, cold-formed portal framing system that comprises tapered box members formed from two cold-formed nested channel sections. The proposed method possesses structural and nonstructural advantages, such as improved seismic performance, enhanced building hygiene through bird and dust resistance, further corrosion resistance, and aesthetic improvement, as a result of fly bracing removal. The novelty of the box member lies in the tapering ability of the section, leading to material and paint savings. To examine the failure mechanisms and structural performance of the tapered box portal frame and to investigate the adequacy of the design method, two full-scale portal frames with an 18.16-m span were built and tested to failure under two common loading scenarios. The first was lateral cyclic loading into the inelastic range in conjunction with a vertically acting permanent load. The possibility of ductile plastic hinge formation in a severe earthquake was investigated using lateral cyclic testing. The second was vertical loading to failure. A novel economic loading setup was used to apply the gravity load on the frame. For the seismic design of this section type, slenderness limits are proposed for seismic applications along with the design ductility. A rotational stiffness value for a nominally pinned portal frame column base was also suggested in this study. 

Full-Scale Experimental Tests on Portal Frames Comprising Novel Cold-Formed Tapered Box Sections

This paper presents the experimental results of loading tests on two 18 m span tapered member portal frames designed to BS 5950. Deflection test results for vertical, lateral and combined loading cases are compared with the predictions given by elastic analysis to BS 5950 and shown to be favourable. The predicted ultimate capacities and modes of failure, which were by lateral–torsional buckling of the columns, were also found to agree with the experimental behaviour. It was found that the method of modelling the tapered members as a series of prismatic elements gave good comparison with test results.

J. C. Leinster

Papers

Novel loading tests on full-scale tapered member portal frames