THE FIRST THERMAL ANALYSIS OF AN ARCH

The engineers of the 18th century were well aware of the movements suffered by arch bridges due to changes of temperature. In 1801 this problem caused concern to the experts reporting on Telford’s design for a 600 feet iron arch. Vicat reported in 1824 “un mouvement périodique ” in the arches of the bridge of Souillac and George Rennie published in 1842 the movements observed in Southwark Bridge after its completion in 1818. However the analysis of these perturbations was studied much later, within the frame of elastic theory, by Bresse in 1854 and Rankine in 1862, followed by others like Winkler or Clapeyron, in the last quarter of the 19 th century. This is the information that can be found in the general books on the History of the Theory of Structures. In fact, Thomas Young included in his article “Bridge ” written for the Supplement to the fourth edition of the Encyclopaedia Britannica, and published anonymously in 1817, an analysis of the thermal effects in an iron arch bridge. He deduced first the general expression for shallow segmental arches and then applied it to the arch of Southwark Bridge. Thomas Young’s analysis preceded, then, by ca. 40 years the work of Bresse or Rankine. However he received no recognition for this discovery, and it appears that no contemporary English engineer was able to understand his derivations