GBTUL (acronym for “GBT at the University of Lisbon”) is a freeware program that performs elastic buckling (bifurcation) and vibration analyses of prismatic thin-walled members. It implements the latest formulations of Generalised Beam Theory (GBT), a thin-walled bar theory that (i) accounts for local deformation and (ii) provides an advantageous representation of the deformation field, as a combination of structurally meaningful cross-section deformation modes.

Taking advantage of the GBT modal features, the program provides information and visualisation of the member deformation modes. Moreover, it contains tools that make it possible to select the deformation modes to include in the analysis, thus allowing for a in-depth insight into the mechanics of the problem being solved. It is possible to analyse members (i) made of one or several isotropic or orthotropic materials, and (ii) exhibiting various common support conditions (e.g., simple supports, fixed supports or free ends). In the buckling analyses, the user is able to specify any combination of arbitrary axial force, bending moment and bimoment (longitudinal) diagrams.

GBTUL contains a user-friendly and intuitive graphical interface (i) with a small number of commands and (ii) providing high-quality 2D and 3D outputs.

This program was developed at the Department of Civil Engineering (DECivil) of the Technical University of Lisbon (UL) – Lisbon, Portugal – with financial support from the Portuguese Foundation for Science and Technology (FCT – see “Acknowledgements”).