The Ardant truss: a forgotten rival of the well-known Polonceau truss

In 1839 the engineer Camille Polonceau invented the structurally efficient Polonceau truss. However, for a long time architects refused to leave iron structures exposed in public buildings for aesthetical reasons. Despite this, engineers acknowledged the ample structural opportunities of iron roofs, which urged them to experiment with curved trusses in order to avoid the bar roof trusses so reminiscent of industrial buildings. Nevertheless, today everyone knows the Polonceau truss, whereas few are familiar with its aesthetical counterpart: the Ardant truss.
This curved roof truss makes use of an inscribed arch, tangential and framed to the principal rafters of a gable roof, in order to add rigidity to the roof structure and avoid interfering tension ties. According to the spirit of those times, this solution with its high decorative potential seemed to provide a satisfying answer to both the aesthetical as well as the structural problems of iron roof trusses in public buildings. Subsequently, it was used many times in swimming pools, stock exchange buildings, schools, platform coverings, palaces, malls, etc.
In Belgium it was widely used to span the central covered courtyard of the Brussels model schools which were built between 1875 and 1920 and which were very innovative with regard to their architecture, educational policy, hygiene, heating and ventilation techniques, safety, etc.
This paper deals with the ongoing debates on the efficiency and aesthetics of iron architecture in the 19th and 20th centuries by analysing the truss designs of three Brussels model schools.