Introduction

Last week we explored the reaction of structures to bending and also looked at structures that contain some level of redundancy which makes them statically indeterminate. Statically indeterminate is a term used to describe our inability to analyse reactions and internal forces associated with these structures using only the equations of static equilibrium. We resolve this problem by considering imaginary or virtual displacements of the structures and using compatibility of displacements. So far in this course we have tried to simplify and idealize structures. We have done this so we can model them using relatively simple ideas and mathematics.

This week we are going to inject a bigger dose of reality in two ways, first by recognising that structures experience tensile loads, compressive loads and bending moments, as well as torsion loads, often all at once. And second, by considering how the materials that we use to make our structures react to the stresses and strains imposed on them. In week two we use chocolate biscuits to illustrate the effects of a torque. This week we use chocolate bars and you might need your credit card, though not one that you ever plan to use again.