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An Italian-American investigation has revealed the secret of domes built without the use of formwork or scaffolding. This science can be very useful for modern applications.

Now that the secret of building scale structures has been uncovered, a new world is opening up. This is the firm belief of Sigrid Adriaenssens, senior lecturer in civil engineering and environmental engineering at the prestigious University of Princeton, New Jersey. With her department and in collaboration with the engineering faculty of the University of Bergamo in Italy, she studied how self-supporting brick domes were built in the Italian Renaissance. Such domes were erected without the use of scaffolding or formwork. The results are described in the July issue of the journal “Engineering Structures” (Publishers Elsevier).

Domes have been the greatest architectural challenge for centuries

Scale constructions, such as domes, have been regarded throughout history as one of the most difficult tasks in architecture. The icon of the self-supporting shell construction is the dome of Florence Cathedral, construction of which began exactly 600 years ago. Apart from the large cross-section of the dome (45 meters), it is remarkable that architect Filippo Brunelleschi did not use formwork or scaffolding during construction. The researchers did not investigate the Florentine dome, but a similar one in Montefiascone in Lazio, Italy.

“The Renaissance dome we investigated,” says Adriaenssens, “was built with horizontal layers of brick between which vertical bricks were laid in a fish-scale pattern. These vertical bricks are arranged according to a curvature, which in geometry is called a rhombus line.”

The crux is that the horizontal bricks, which tend to slide inwards in dome construction, cling to the vertical bricks. In this way the bricks are stuck, so to speak. “The vertical bricks are similar to bookends between which books are placed,” says the Belgian professor. The mortar doesn’t even have that much influence on the stability of the dome during construction.

“By the way, the herringbone motif had been known since the Romans, who called this type of masonry ‘opus spicatum,'” says Sigrid Adriaenssens, senior lecturer in civil construction and environmental engineering.

Adriaenssens and her team used computer calculations based on so-called “discrete element modeling” (DEM), in which the interaction between each particle, in this case a brick, is analyzed. In the case of DEM, each individual element needs to be scrutinized. “How does a brick react when you place another one against it, and what if two bricks are added, and three, et cetera? What are the forces, what tensions build up? It’s very precise work,” says the Belgian professor, who obtained her master’s and doctoral degrees in the United Kingdom.

Adriaenssens believes that we can take advantage of this new insight. After all, scale constructions still require formwork and scaffolding for support. That costs money and leads to waste. “For scale constructions such as a dome, the dome must first be made of wood that is used as a support and mold. On that dome you pour concrete or place bricks. Then the wood is removed and processed as construction waste.” Thanks to this new insight into dome construction, modern robot technology can be used to build according to Brunelleschi’s philosophy.

The first example of a modern, self-supporting shell construction was carried out earlier this year at the exhibition “The Anatomy of Structure” at the Ambika Gallery in London. It showed how two robots (one picks up the brick, the other supports the point at which the brick is placed) independently built a dome.

Dome of glass bricks

The span was transparent because the makers, in consultation with the Delft University of Technology, opted for glass bricks. Glass works well when there is pressure on it. Instead of mortar, epoxy glue (a two-component adhesive) was used. For this small dome (3.6 by 6.5 meters with a height of over two meters) a total of 338 bricks was used. This is not comparable to the estimated 4 million bricks of Brunelleschi’s dome; however, the principle is the same. This proves that even modern constructions can be built with modern materials according to the principle of laying alternating horizontal and vertical bricks.

The new technique offers many possibilities, such as in places that are difficult to reach or dangerous or in places in the city where there is a lot of traffic. Adriaenssens wants to continue along this path. She wants to know whether there are patterns other than herringbone that can be proposed for the construction of self-supporting scale structures. She also imagines that drones will be able to build domes in the future. The problem here is that drones have little bearing capacity and are not very good at precision work.

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