Young Researcher: Sinéad Smith email: S.E.Smith-2@sms.ed.ac.uk
Establishment: University of Edinburgh
Supervisor: Prof. Michael Rotter email: Michael@civ.ed.ac.uk
Aims of research:
Metal silos storing granular solids are very susceptible to axial compression shell buckling, and failures are common in all countries. The buckling strength is greatly enhanced (typically 3x) by internal pressure from the stored solid: this strengthening is exploited in silos and spacerockets. However, pressures from solids are not perfectly symmetrical, and local temporary reductions in pressure may easily occur. This study is the first ever to explore the sensitivity of the buckling strength to local internal pressure reduction: it involves a parametric study of bifurcation, imperfection sensitivity, and varying areas and magnitudes of pressure loss, with plasticity if necessary.

Description of method:
The study of shell buckling will be undertaken computationally using the program ABAQUS, which is well able to follow the bifurcation and post-buckling response of the difficult phenomenon of shell buckling. The calculations must include modelling of the buckling of axially compressed cylinders with various amplitudes of imperfections, modelling the effect of internal pressurisation in increasing the strength, and of local reductions in pressure on different areas of shell, taking into account the size and shape of potential buckles that may form. The length of the shell may have a marked effect, so this will be included.

The study will partly be undertaken at the French university INSA de Lyon, where an extensive research programme has been undertaken over the last eight years of experimental and theoretical work on pressurised cylinder buckling under global bending (in connection with Arianne rocket design). This project produced four PhD theses. INSA will provide extensive quality experimental data for verification purposes, together with access to computational facilities, without charge.

This application seeks funding to exploit the opportunity of collaborative Work with INSA. The funds sought will permit me to travel to Lyon and will cover my living costs whilst there. They will also permit me to extend and complete the study after my return, using the summer following my graduation and before PhD research. This project will considerably enhance my skills in computational modelling of highly nonlinear structural problems, and develop my skills in transforming results into rules for design standards. It should provide a very effective training in structural engineering research.

The study should finally produce a carefully calibrated, safe rule that indicates the susceptibility of shell buckling to local loss of internal pressure. It will be especially valuable for silos under eccentric discharge, which has caused many failures.

Benefits to structural Engineering:
The project will lead directly and immediately to modification of the Eurocodes for Shell Structures (ENV 1993-1-6) and Silos (ENV 1993-4-1) which are being upgraded to mandatory EN standards in 2003 under the convenorship of Prof. Rotter. This study has the potential to reduce the incidence of silo failures significantly, and to raise international awareness of a shell buckling problem that has never been studied. It will also be one of the first studies to explore shell buckling under unsymmetrical loads, which occur quite widely in practice but have rarely been researched at all.