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Mailart's beamless slab (mushroom slab), testing site
Giesshubel, Zurich, Switzerland
Mailart's beamless slab (mushroom slab), testing site
associated engineer
Robert Maillart
Maillart & Cie
date  1908 - 1909
era  Modern  |  category  Building  |  reference  Tf939715
photo  copyright ETH-Bibliothek Zürich, Bildarchiv
Robert Maillart’s transformed reinforced concrete design in the early 20th century. He strove to make structures as strong and economical as possible. In 1908, he developed a system for supporting floor slabs directly on columns without the need for beams, a system that he patented in 1909. Many of the buildings constructed using his method are still in use in Switzerland.
A beamless reinforced concrete system is cheaper to construct than a more traditional matrix of slab, beams, secondary beams and columns. It uses much less concrete and steel, and provides more usable space for the same floor-to-floor height. Maillart was also interested in the way things looked, seeking to eliminate any details he thought unnecessary.
For a slab of constant thickness carried only on columns, the shear forces and bending moments are greater over the columns than elsewhere. To absorb the forces, Robert Maillart (1872-1940) proposed widening the tops of the columns. The arrangement of flared column heads below a slab was variously known as ‘mushroom columns’, ‘mushroom slabs’ or ‘beamless slabs’.
While Maillart was working independently, similar ideas had been developed and were being put into practice elsewhere. American Claude Allen Porter Turner’s (1869-1955) and Russian Artur Ferdinandovitch Loleit’s (1868-1933) first buildings with beamless slabs and mushroom column heads were built in 1906 (uSA) and 1907 (Russia) respectively.
However, in 1908 no accepted methods of calculation for predicting the forces that might be acting on the columns existed, making it difficult, if not impossible, to know the size of columns or quantity and layout of reinforcement required.
Maillart had long been an advocate of exploring design by physical and graphical testing rather than mathematical calculation. He explored the beamless slab idea by building and load testing large-scale reinforced concrete models at his construction yard in Zürich. As this location is unknown, the site of Maillart's first beamless slab built project, Giesshübel warehouse (1910), is marked on the map.
Testing began with not-quite full height single-storey reinforced concrete frames consisting of slabs resting on single-bay and three-bay square arrangements of columns. The top surfaces of the slabs were loaded with sandbags and the results observed.
By 1909, he had built a reinforced concrete three-bay square ‘room’ with solid walls on two sides and along part of the third side (pictured). The columns were octagonal in section with curved capitals. The ‘roof’ could be loaded at any point by weights suspended from a steel girder spanning between mobile towers running on rails parallel to the open side of the room. Inside the structure, a plethora of measuring devices and gauges were set up to monitor any changes and deflections.
Maillart’s testing led to columns with hyperbolically splayed tops and a grid of two-way spanning reinforcement in the slab over the column heads. On 20th January 1909, he obtained a patent (no. 46,928) for his beamless system of slab and columns. The system was used very successfully by Maillart in more than 50 buildings constructed in his lifetime.
Contractor: Maillart & Cie
Research: ECPK
"The History of the Theory of Structures: from Arch Analysis to Computational Mechanics" by Karl-Eugen Kurrer, John Wiley & Sons, June 2008
"Robert Maillart: Builder, Designer, and Artist" by David P. Billington, Cambridge University Press, 1997
"Robert Maillart and the art of reinforced concrete" by David P. Billington, Architectural History Foundation, MIT Press, 1990
"Robert Maillart's bridges: the art of engineering" by David P. Billington, University Press, Princeton, New Jersey, 1979
"Robert Maillart: Bridges and Constructions" by Max Bill, translated by W.P.M.K. Clay, Pall Mall Press, 3rd revised edition, November 1969

Mailart's beamless slab (mushroom slab), testing site