2007 Higher Degree Theses

The following postgraduate students were awarded higher degrees for their theses in 2007.

Doctor of Philosophy

Gabriele Eccher, Isoparametric Spline Finite Strip Analysis of Perforated Thin-Walled Steel Structures

Gabriele Eccher
Isoparametric Spline Finite Strip Analysis of Perforated Thin-Walled Steel Structures
Supervisor: Riccardo Zandonini, University of Trento
Supervisor: Kim J. R. Rasmussen, The University of Sydney
Joint PhD awarded by both The University of Trento and The University of Sydney

Perforated thin-walled cold-formed steel structures are very common in many aerospace, naval and civil applications. They combine high structural performance, pleasant esthetical appearance and light weight, and offer optimal technical solutions to many primary and secondary structures. The present thesis investigates the structural analysis of perforated structures, notably cold-formed structures and cold-formed steel storage rack structures in particular. The complexity and variety of the shape of cold-formed cross-sections and their sensitivity to buckling lead to complex stress distributions in the presence of openings. Consequently, the design of perforated rack uprights is particularly complex, usually involving sophisticated numerical simulations and/or extensive experimental tests. The finite strip method has proved to be an efficient numerical tool for the structural analysis of prismatic non-perforated thin-walled structures. It offers a remarkable computational economy compared to the finite element method, by requiring a much lower number of degrees of freedom for a given geometry. Originally limited to simple boundary conditions and geometries, the finite strip method has been complemented by the spline finite strip method and by the isoparametric spline finite strip method to allow for the modelling of arbitrary loadings, geometries and boundary conditions.

The aim of the present thesis is to develop an advanced numerical tool which applies the computational efficiency of the spline finite strip method with an isoparametric mapping technique to analyse the complex behaviour of perforated thin-walled structures. The analysis will help to further the design and research on perforated thin-walled structures in general, and perforated rack uprights in particular. In the thesis, the isoparametric spline finite strip method is hence extended to the structural analysis of perforated thin-walled structures by devising a new technique for the assembly of spline finite strips in perforated areas. The proposed method has been coded in a fortran computer program and applied to the linear elastic, elastic buckling and geometrical nonlinear structural analyses. Numerical routines have been created as part of developing these analyses, offering accurate and economical solutions to large linear systems, large generalised eigenvalue problems and complex nonlinear structural problems. The accuracy of the isoparametric spline finite strip method is assessed in a number of examples by comparison with analytical and established numerical solutions as well as new solutions for perforated sections obtained by finely meshed finite element analyses.

Furthermore, experimental tests have been performed in order to investigate the effect of perforations and extended rear flanges on the buckling behaviour of industrial rack uprights. The tests were performed on a series of perforated and non-perforated sections and were used to confirm the accuracy of the isoparametric spline finite strip method by comparing the experimental readings of displacements and strains in perforated areas with those obtained by the isoparametric spline finite strip analysis.

Download Gabriel Eccher's thesis (8.4 MB PDF)