Out of his shell: Giorgio Baroni, an early designer of hyperbolic paraboloid shells

Martina Russo is a PhD student at Sapienza University of Rome, and recent Visiting Research Student Collaborator at Princeton University (Form Finding Lab, Department of Civil and Environmental Engineering, and Chaos Lab at the Andlinger Center for Energy and Environment).


Reinforced concrete thin shell structures are nowadays considered as part of the architectural and engineering heritage of the 20th Century. Today, a number of these structures can be admired around the world, especially the masterpieces of the “master builders:” Felix Candela, Heinz Isler, and Pier Luigi Nervi. Although these designers developed their main projects around the 1950’s and 60’s, this structural typology was the outcome of research on the relation between form and structural behavior begun in Europe in the 1920’s.

Many years before the zenith of reinforced concrete shells, some pioneers in Germany, France, Spain, and Italy began experimenting with and filing patents for new construction systems capable of spanning large distances efficiently. Notably, Franz Dischinger and Ulrich Finsterwalder developed domes and barrel vaults in partnership with Dyckerhoff & Widmann and the Zeiss Company. These optimized systems were the first thin concrete shell structures.

Who were these pioneers? How did they develop their projects? What was their design method? How much were they aware about the real structural behavior of thin shells they designed. These are some of the questions that motivate the present research on the construction of thin shell concrete roofs designed by the Italian engineer Giorgio Baroni (1907-1968), one of the early thin concrete shell structures pioneers in Europe. Of particular interest is his unique design method and the structural behavior of his geometries, as well as the relation between form and structure.

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Figure 1. From the left: eng. Giorgio Baroni when he was around thirty; Baroni’s patents for gabled-type and umbrella-type hypar roofs; the conoid shells of ATAC’s workshop in Rome during construction, 1939.

To answer these questions, I began with a biographical study of Giorgio Baroni and his projects, through archival research, architectural, and construction surveys. Additionally, I implemented and validated a finite element model of one of his buildings to evaluate how closely its structural performance matches the designer’s expectations. This research will hopefully promote awareness of historical construction solutions, identify specific attributes of modern buildings as heritage, and develop a method to preserve, restore or transform them.

Giorgio Baroni: a shell pioneer

Giorgio Baroni can be credited as the first Italian engineer to patent a construction system for roofs formed by four sections of the hyperbolic paraboloid (often refer to hypar). The first patent was filed in 1936 and a second in 1949. Baroni’s patents were developed during the autarchic period of fascism when reducing the use of steel in construction was a priority. Baroni became interested in the warped surfaces, in particular, the hyperbolic paraboloid, which offers advantages in terms of construction technique.  Being a ruled surface, it is economical to build the scaffolding and arrange the rebar along the direction of the directrix of the geometry, while maintaining an anticlastic curvature. With these features, Baroni achieved a competitive construction system, capable of optimizing the use of construction materials, especially of steel, while minimizing the shell thickness.

The above two patents differ in the position of the shell supports and in the arrangement of the sections of the hypar. The first patent (n. 346696, filed in 1936) described a gabled-type roof, with four columns at each corner. Edge beams and ridge beams are run along the edge of each hypar section, while tie beams span between the columns in order to control the displacement of the corners. Such a construction system does not require scaffolding for the casting of the hypar, since shotcrete could be placed directly on the rebar grid. The second patent (n. 450290, filed in 1949) illustrated an umbrella-type structure, with a singular column. As in the previous case, edge beams support each section of the hypar, but for this arrangement, scaffolding is required to cast the shell.

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Figure 2. The cinema-theater at the Vanzetti steelworks Milan during construction. Milan, 1936.

The unique systems described in both these patents offered an economic and rapid means of spanning large distances, compared to other systems available at that time. With these systems, he designed various structures in Italy: a cinema-theater for the Vanzetti steelworks (1936) and an iron-working building for the Alfa-Romeo factory at Portello (1936), both in Milan, a hemp warehouse in Tresigallo (Ferrara, 1940), as well as a number of market halls in Rome and Caserta. He also experimented with the northern light conoid shed roofs, designing a workshop for public transport in Rome and a textile factory in Tresigallo (Ferrara), both around 1939.

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Figure 3. The umbrella-type roof of the warehouse in Tresigallo during construction, 1939-40. 

Structural mechanics for construction history

During the early period of thin shell construction, the predominant design approach was based on membrane theory. This theory allows designers to neglect the bending strength in very thin shells, considerably simplifying engineering calculations. However, bending stress is not completely absent in these shells. Especially near the edges, bending has a significant influence on the joints between shell and edge support members. Using this theory, engineers could not have had a full understanding of stress transfer from the shell to the edge beams.

Contrary to other thin shell pioneers of that time, e.g. Fernand Aimond, Baroni chose incredibly slender sections for his edge members. His roofs combine lightness and strength, not only in the thickness of the shell, but also in the edge beams. How was Baroni able to efficiently combine form and structural performance, going much further than other designer of that time? And did his projects really perform how Baroni had predicted?

These questions have led the historical research to a structural mechanics investigation. In depth structural analyses are still in progress, but considering the preliminary results, it seems that Baroni was able to estimate correctly the effect of the bending moment along the edges and chose the most suitable section ratio for each element. The interaction between shells and edge beams was not fully analyzed before the 1970’s, when early software based on the finite element method first became available for thin shell analysis.

End note

This research is based on the belief that a deep knowledge on construction features of historical structures can help to evaluate their performance and to adopt the best approach to preserve them. This type of methodology could be especially significant in the case of thin concrete shells due to the particular technique applied. Understanding the characteristic behavior of these systems and the limitations in terms of durability of the reinforced concrete can help guide conscious decisions during increasingly necessary renovations.


References

Currà E., Russo M. (2018) Reinforced concrete in Italy through the works of two generations of engineers: Mario and Giorgio Baroni. The 6th International Congress on Construction History – July 2018, Brussels.

Russo M., Currà E. (2018) The diffusion of the Zeiss-Dywidag system in Italy: two cases in Rome. The 6th International Congress on Construction History – July 2018, Brussels.

Russo M. (2018) Conoid surfaces by Giorgio Baroni for thin concrete shell roofs. ArTec/Colloquiate Congress – September 2018, Cagliari.

Acknowledgements

This research has developed during the PhD program in Engineering-based Architecture and Urban Planning at Sapienza University of Rome, advised by prof. eng. Edoardo Currà (Sapienza University of Rome, department of Civil Building and Environmental Engineering).

The author would like to also thank prof. eng. Stefano Gabriele (University of Roma Tre, department of Architecture) for his valuable advice and the support in the development of the model.

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