Bill Harvey Associates Ltd


There is a growing tendency to turn to finite elements as a panacea of analysis. The author’s experience is that, even when the work is carried out by very experienced engineers, faith in the computer is often uncritical and care and understanding from the engineer equally inadequate. Simple tools and exploration of limits of behaviour often yield deeper understanding. That understanding is the only proper foundation for the confidence required when signing off complex existing structures for new uses or for alteration.
The paper begins with a brief description of thrust line analysis and how it can be done in a spreadsheet.
A brick lined tunnel was analysed using complex finite elements and major strengthening works proposed. An interactive analysis, based on graphical equilibrium, was constructed and showed that the structure could sustain substantial movement without loss of stability. A saving of around €20m was achieved.

Key words
Analysis, Equilibrium, Spreadsheet, Interaction, Exploration, Tunnel, Viaduct