Some Paradoxical Experiments on Beams

Abstract

Most experiments on structures that are performed by university students as part of the curriculum are designed so that the experimental observations are in accord with the theory that has been presented in the lectures. In this paper I describe an experiment that forms part of the second-year Engineering course at Cambridge, in which each of four different beam-like specimens deflects, under load, in a way that is contrary to expectations based on the usual ‘engineers' bending theory’ as taught in lectures. The key to the situation is that various assumptions that underlie the theory are not applicable for the particular structures under investigation. With some help from the demonstrator, the students work out what is happening, and devise tests that confirm their hypotheses about the paradoxical behaviour that they have encountered. Thus the experiment deepens the students' understanding of the theory of beams. The paper concludes with a discussion.