Double helix — the secret of Italian renaissance domes

The Sangallo, who created their own self-balanced building method for brick domes based on the cross-herringbone spiraling pattern in the 16th century, were undoubtedly aware of the Brunelleschi herringbone pattern. For almost a century, this method was utilized in Italy to construct brick domes without the need of shoring or formwork. However, it is currently unknown how this cross-herringbone spiraling design allows self-balancing brick domes to achieve equilibrium states.

Researchers looked at how cupolas, such as the iconic duomo at Florence’s Cathedral of Santa Maria del Fiore, were designed to be self-supporting, without the use of shoring or forms that are usually necessary.

The study is the first to statistically show the physics at work in Italian Renaissance domes and to explain the forces that allow such buildings to be erected without the use of formwork, which is generally necessary even in modern construction. Previously, there were only ideas in the field regarding how forces flowed through such structures, and it was unknown how they were constructed without the usage of temporary structures to hold them up during construction. For Adriaenssens, the project advances two significant questions.

“How can mankind construct such a large and beautiful structure without any formwork—mechanically, what’s the innovation?” and “What can we learn? Is there some forgotten technology that we can use today?”

Double helix of masonry -- Researchers discover the secret of Italian renaissance domes
The double loxodrome technique is comprised of rows of vertical herringbone bricks that spiral around the dome and are filled in by horizontal field bricks. Effectively, each course of bricks creates a structural element known as a plate-bande or flat arch that wedges interior bricks between the vertical end caps to distribute load throughout the structure. 
Sail of an octagonal dome: brick pattern the elements highlighted: nodes (top), horizontal courses (middle), herringbone bricks (bottom) (left). Left and right-handed loxodromic curves (thick lines) and rhombi (areas filled) (right)

The thorough computer study accounts for all of the forces at action, down to the individual brick, and explains how equilibrium is achieved. The structure was studied using a technology known as discrete element modeling (DEM) at various levels and stages of development. The total equilibrium state, or stability, of the finished structure, was assessed using a limit state analysis. Not only do these tests verify the mechanics of the structures, but they also make it possible to recreate the techniques for modern construction.

The cross-herringbone spiraling pattern enables the building of self-balancing domes and the development of plate-bande action between two herringbone bricks. Even throughout the building stages, the friction of the mortar has no effect on the dome’s stability. The limit state analysis analyzes the stable equilibrium of the cross-herringbone dome while it is being built.

This discovery will have practical implications in creating building procedures that include airborne drones and robotics. The use of these autonomous robots in construction would boost worker safety while also increasing construction pace and lowering building expenses.

The disruptive potential of this historic masonry pattern comes to the fore for today’s construction industry when this technology is viewed in the context of other emerging innovations such as novel structural form finding approaches and robotic construction technologies

Statics of self-balancing masonry domes constructed with a cross-herringbone spiraling pattern, Vittorio Paris, Attilio Pizzigoni, Sigrid Adriaenssens

Published: Apr, 2020

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