The Bélidor Bascule Bridge Design

Abstract

A trunnion-type drawbridge requires a lifting force that varies in the course of its operation. The so-called Bélidor design allows for this variation by providing a counterweight running down a curved track whose shape is calculated to provide the correct effective force during the course of the lift. The design is usually attributed to the eighteenth-century engineer Bernard Forest de Bélidor, but in fact is earlier. We provide a correct account of the origins of the design and go on to discuss its implementation in a variety of places and contexts. It was used in eight examples constructed in the Australian state of New South Wales in the first quarter of the twentieth century, where the consideration was to accommodate the competing demands of road/rail transport and of shipping. The same design had also been used somewhat earlier in the USA for the same purposes. We provide a guide to the literature dealing with both these sets of examples. Moreover, as well as the Australian and American examples, there are others in Europe, mostly as elements of castle fortifications. The reader is introduced to a number of these. We also discuss a very recent example (Forton Lake) developed for other purposes, as well as a further American example (Glimmer Glass). These two examples are noteworthy in that both are fully operational. We also provide the basic theory underlying the design and comment on the different ways in which it has been realized.

Keywords:

• bascule
• Bélidor
• bridge
• cardioid
• counterweights

We thank Alberto Ferrara for his help and for Figures 3 and 4, Rayda Jenkinson for Figures 5 and 6, and Monash University for permission to reproduce Figure 1.

Additional information

Notes on contributors

Fabrizio Barpi

Fabrizio Barpi is an Assistant Professor of Structural Mechanics at Politecnico di Torino, Italy. He graduated in Civil Engineering from Politecnico di Torino and obtained a PhD from the same University with a thesis on numerical models for the study of cracking phenomena in dams. His research interests are focused on nonconservative continuum mechanics, fracture and computational mechanics, and, recently, snow avalanche dynamics. He has cooperated with the Department of Civil Engineering and Geosciences of Delft University (the Netherlands). He has taught Structural Mechanics and Theory of Elasticity courses at Politecnico di Torino.

Correspondence to: Fabrizio Barpi. Email: [email protected]

Michael A B Deakin

Michael A. B. Deakin is an adjunct Senior Researcher and former Senior Lecturer at Monash University, Australia. He is an applied mathematician with a wide range of interests, including the history of Mathematcs. He holds the degrees of MSc (Melbourne), MEd (Exeter), and PhD (Chicago), and among other things has written a four-part history of the Laplace transform and, more recently, a biography of Hypatia of Alexandria. He has taught Engineering Mathematics at both the University of Melbourne and at Monash. More widely, he has taught Mathematics in the USA, the UK, India, Indonesia, and Papua New Guinea.

Correspondence to: Michael Deakin. Email: [email protected]