The load-carrying capacity of a beam, either prismatic or tapered, is usually assessed on the basis of its (i) cross-sectional strength and (ii) elastic lateral-torsional buckling strength. However, the warping-torsion behaviour of prismatic and tapered thin-walled beams is, in general, qualitatively different. This means that the piecewise prismatic modelling of a tapered beam for the purpose of lateral-torsional buckling analysis is frequently incorrect and may lead to significant errors [2,3,4]. There is thus a clear need for methods capable of accurately predicting the elastic critical buckling load factor of a given tapered beam at a low computational cost; the use of shell or solid finite-element models is excessively time-consuming and computationally expensive for routine applications.

This paper presents an user-friendly finite-element tool for the elastic buckling analysis of tapered I-beams, named LTB-UC, which is based on the one-dimensional model developed and validated in References [2,3]. It is capable of handling singly symmetric I-beams, loaded in the plane of symmetry, which are built-up from constant-thickness plates cut to trapezoidal form or fabricated by reassembling split rolled profiles. Moreover, LTB-UC can also deal with assemblies of several such segments. The connections between segments may exhibit a break in the mechanical continuity of the flanges, in which case they are deemed incapable of transmitting bending moments and bimoments and modelled through the concept of generalized hinge. The in-plane and out-of-plane restraints, either rigid or elastic, are for the moment necessarily discrete, but the consideration of continuous braces is currently being addressed. The allowable external loading includes piecewise uniform and concentrated transverse forces, applied at an arbitrary level, as well as quasi-tangential moments.

The data-input process is streamlined by a user-friendly graphical interface, which was designed to alleviate the effort involved in the preparation and checking of the data and in the interpretation of the results. In problems that exhibit certain regularity features, the data input process is automatically simplified. Variations in some of the design parameters can be readily assessed. A practical example illustrates the capabilities and versatility of LTB-UC. LTB-UC will be made available to the structural engineering community as freeware.

1

D.P. Billington, "The Tower and the Bridge The New Art of Structural Engineering", Princeton University Press, 1985.

2

A. Andrade, D. Camotim, "Lateral-torsional buckling of singly symmetric tapered beams: Theory and applications", Journal of Engineering Mechanics - ASCE, 131(6), 586-597, 2005. doi:10.1061/(ASCE)0733-9399(2005)131:6(586)

3

A. Andrade, D. Camotim, P.B. Dinis, "Lateral-torsional buckling of singly symmetric web-tapered thin-walled I-beams: 1D model vs. shell FEA", Computers & Structures, 85(17-18), 1343-1359, 2007. doi:10.1016/j.compstruc.2006.08.079

4

A. Andrade, P. Providência, D. Camotim, "Elastic lateral-torsional buckling of restrained web-tapered I-beams", submitted for publication, 2010.

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