ISSN 2283-7558


Attilio Pizzigoni


Architetto, Professore, Dipartimento di Ingegneria dell’Università di Bergamo

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La geometria reciproca tridimensionale della Spinapesce nella concezione strutturale della Cupola di Santa Maria del Fiore a Firenze

"Si faccia di mattoni grandi ... i quali si murino con quello spinapesce sarà deliberato per chi l'avrà un conducere ... e murisi con gualandrino con tre corde ... " , così sta scritto nel Rapporto dei Provveditori del 24 gennaio 1426. L’obiettivo di questo scritto è quello di studiare la geometria spaziale dell’ammorsamento dei mattoni e la loro configurazione all’interno dello spessore della volta del Duomo di Santa Maria del Fiore a Firenze. "Spinapesce " è la parola che viene utilizzata per descrivere questa particolare posizione dei mattoni, ma raramente la letteratura in proposito accenna alla giacitura tridimensionale dei mattoni e al loro reale allineamento all’interno della geometria della Cupola.

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Reciprocal tridimensional herringbone volting Brunelleschi’s Dome in Florence

“Si faccia di mattoni grandi ... i quali si murino con quello spinapesce sarà deliberato per chi l’avrà a conducere … e murisi con gualandrino con tre corde…”, quote from Rapporto dei Provveditori of 24th January 1426.
This paper focuses on how the brick bond and masonry pattern are configured inside the dome of the Santa Maria del Fiore Cathedral in Florence, Italy.
“Herringbone” is the word that’s always used to describe it, but there’s hardly a mention of the true nature of the three-dimensional layers of bricks in the dome’s spatial geometry. This paper intends to address these issues and provide a likely and plausible hypothesis. Said hypothesis is founded on a very special three-dimensional, reciprocal interaction of its bricks, and is verified by virtual models and physical prototypes. The questions this paper intends to answer are:
_How to reach static equilibrium of masonry with or without the contribution of mortars, or else before the final (very slow) setting time of lime mortar – just by relying upon  their three-dimensional reciprocal bonding.
_How to lay such three-dimensional reciprocal bricks on a ring bed with a centre around which all the bricks are aligned, and thus build a shell as a solid of revolution. This the only kind of dome which may be constructed without scaffolding or ribs, as testified by Leon Battista Alberti in De re aedificatoria, Lib.III Cap XIV.
_How to lay these bricks using a very particular device, the so-called gualandrino (a kind of geometric square rule with three rulers not just the usual two), in order to obtain spatial coordinates beyond those two in the plan of brick layers. From this point of view all former and current references to Brunelleschi’s masterwork do not refer to normal, traditional bricks. Instead we discuss the the very unusual, outsized bricks which he himself designed and modelled by cutting experimental shapes from enormous turnips. Their design was so particular that he oversaw their manufacture personally, even as far as the furnaces.
This research indicates a possible procedure that would allow the construction of whole or parts of masonry domes using a non-traditional type of brick, through mountable and demountable reciprocal interaction. Moreover we have employed a parametric modelling software which enables us to generate different shapes by varying the ruling algorithm.