The Volksbad in the small village of Gebweiler, France (located in the region known as Elsace which was part of Germany when it was built) is a superlative representative of the earliest modern public swimming halls built of reinforced concrete. It was designed and built by the Swiss-born structural engineer and contractor, Eduard Züblin(1) between 1898 and 1900. His office was located in Strassburg, Germany at that time. The Gebweiler Volksbad was the first in a series of four public pools that Züblin built in the Elsace. The following three, Volksbad in Markirch (1901-02), Volksbad Unter Linden in Colmar (1904-05), and Volksbad in Strassburg (1905), were almost all duplicates of this design.
The turn of the Century was a very profitable time for this hilly region. It was fortunate in thatit had quite a few small streams that were dammed in order to take create waterpower for small mills. These small, yet significant, industries were booming. The factory owners took some of the profits and built bathing houses/swimming halls for the employees and their families. The Volksbad in Gebweiler was one such natorium; it no longer exists. The Volksbad Unter Linden in Colmar is the only hall existing today in its original form and is thus the hall which is described and discussed below.
The articulation of the interior, as well as the exterior, is dominated by Jugendstil curves and the associated decoration which was in vogue at the time. Only the "monumental" roof vault, the basin, and the small balcony of the 22.60 m long natatorium are built of reinforced concrete; the rest is brick. The roof is articulated as a self supporting fan vault. Yet, it is actually a series of five rigid frames with a 3.5 cm thick Monierdecken spanning (vaulting) between each frame. Each frame has a 1.9 m deep fixed or rigid support which anchors into the solid masonry wall.
The 6.0 m high rigid frames had a 1.5 m deep cross-section and were designed according to Hennebique System. This was due to the fact that Züblin was one of the members of the world-wide group of licensees of Hennebique's reinforced concrete patent. As illustrated above, thin Monierdecke (essentially flat wire-mesh reinforced concrete plates) spanned the 5.5 m between the frames with the help of ribbing. The frames and ribs had a small number of holes punched through them to allow for air circulation. This was intended prevent the build up of condensation in the interstitial space. The fairly flat frames were calculated according to the contemporary methods of graphic statics as rigid arches with a span of 12.3 m.
One of the advantages of purchasing a Hennebique Licence was the support network that Hennebique created. He published a monthly magazine (Beton & eisen) in which experiences could be shared and solutions to problems could be solicited. Züblin took advantage of this and was often a contributer of both questions and solutions. Concrete cracking was a common theme of early issues of the magazine. One of the simple realities of concrete construction was that it cracked as it cured. And, the thicker the cross-section, the more problematic the cracking. Züblin approached the problem of cracking in the massive pool walls from a unique standpoint. He knew that due to the physical properties of the material, concrete would crack due to shrinkage during curing. Instead of fighting this fact, he decided to limit the size of the cracks by making the walls as thin as possible (15 cm) with well distributed shrinkage reinforcing steel. Züblin also had a different solution to supporting the basin. Traditionally, a large hole had been excavated in the ground. Formwork was then built within the void and the earth was used as the second side of the formwork. The concrete was then rammed into place to create very thick walls of massive concrete.
Züblin realized that the temperature fluctuations of the basin could not be completely arrested, and thus designed the supports so that the basin could expand and contract with these variations.(2) The swimming pool was built of ribs and skin, like a ship, and was completely supported on spindle (two-hinged) columns. The basin was solidly fixed at only one end with expansion joints along the other three sides allowing the heated pool and the surrounding structure to expand and contract independently from one another.
Züblin went even further in his considerations of how to heat the hall and the pool. He not only designed a special structure to account for the unique problems of the humid envoronment, but also designed a special heating system that was based on the Roman approach to heating Baths. Hollow walls, floors and ceilings through which heated air could freely pass can be found in this Natorium. The load-bearing structure was designed with holes in all of its members to allow the vertical and lateral flow of air between the cells that were created by the intersecting structural elements. Natural convection created the driving force for this ventialtion system which is still in use almost one hundred years after its construction.
The four Züblin bath houses are designs in which one can clearly find the three influences on the choice of their structural form: Socioeconomic, Building Technology, and Architectural Expression. The hall's construction for a working class clientele was sponsored by the successful local industry. The construction material was due to
"Economical advantages, but also advantages in construction, led to the choice of reinforced concrete above any other material." (3)
There is little relationship between the internal space and the external iconographical form of this building. The "Outside" is a traditional gabled shingled roof which has been built upon the upper surface of the 6 cm slab of the hollow concrete cavity. The pseudo-monumental, coffered and vaulted "Inside" exhibits a surface in which the load-bearing ribs are clearly articulated as part of the decoration. The "In-Between" is cleverly utilized for the functional aspects of the pool, and consists solely of the load-bearing structure.
This is the first public natatorium to be erected of reinforced concrete. It's form does not reflect the unique properties of the material since they were not yet understood. It would only take another twenty years for the engineers and architects to design structures of the material that would be unique.
- Niebelschutz, W. von. Züblin-Bau. Stuttgart: J.G. Cotta'sche Buchhandlung Nachf., 1958.
- Hahn, V. Bauen mit armiertem Beton - Eduard Züblin. Published in the Series VDI-Gesellschaft Bautechnik: Heft 2. Düsseldorf, 1984. p. 8.
- Schürch, H. Das Volksbad in Colmar i. Els. Beton und Eisen, Heft I, 1906. p. 8ff.