ABSTRACT
The French engineer and constructor Camille Polonceau (1813-1859) exploited the principle of how a slender beam can be reinforced by adding a small transverse compression member below its center and tying the lower end of this strut by means of tension rods to the ends of the beam. By inclining two such reinforced beams toward each other and further connecting the ends of the two compression struts with a horizontal member in tension, Polonceau designed a very effective structure for large roofs. In this way the two beams were held in position and at the same time he gained greater spatial height than could be achieved with a traditional roof structure having a horizontallowerflange. The structure made use of the available materials of that time in an optimal way: for the beams he mostly used wood while the compression struts were made of cast iron and the tension ties of wrought iron. This so-called Polonceau truss, well suited for long spans, was used extensively in large hall projects during the 1840s. From a contractor's point of view, the structure had the advantage of consisting of two symmetrical parts; each could be assembled separately on the ground, then lifted up and connected at the top and across at middle height by means ofthe horizontal tie.
