The iron roof trusses of the New Hermitage in St. Petersburg - Structural Survey, analysis and assessment of a masterpiece of structural steelwork from the 1840s.

The New Hermitage of St. Petersburg, planned from 1839 and opened in 1852, is the last building erected in the collection of the former imperial palace complex. Commissioned by Tsar Nicholas 1st and designed by the German architecht Leo von Klenze as a museum for the imperial art collection, with its impressive sets of rooms and its pure classical fassades it now forms the core of the exhibition rooms of the State Hermitage Museum of St. Petersburg (fig.1) along with the 18th century baroque buildings of the Winter Palace, the little and the big Hermitage (fig.2). The collection and the buildings have recently been recognized as Cultural Heritage of the World by UNESCO. The iron roof trusses of the New Hermitage in St. Petersburg, erected in 1844-45, are for the most part preserved in their original state (fig.3). They are mainly composed of closely aligned trusses without purlins, following the principle of the “cable-trussed girder” similar to the later well known “Polonceau”System. This load-bearing system has been systematically recorded and precisely analysed for the first time. The existing method of “Historische Bauforschung” (architectural historical research), itself a branch of construction history, which has become established in Germany over the past few decades, has for this purpose been expanded with engineering-specific components. A structural survey was added to the existing elements of the geometrical survey of construction and the documentation and analysis of the available archive material. This development allows additional information on the function and structural behaviour of components, the origin and manufacture of the material used as well as the planning and assembly process to be recorded. This in-situ research combined with the analysis of materials forms the basis for further practical as well as academic analysis. This paper presents an overview of the survey and an initial assessment and analysis of the results. In addition to a statical analysis of the current state of the structure, a comparison and assessment of the different types of roof trusses extant in the State Hermitage complex is included. These trusses were designed by 3 different engineers in under a 10 year period, using the same structure but varying details, prompting a discussion of the quality of the engineering design.