NevilleBetween 1852 and 1854 Alfred Neville completed the new Accademia bridge, a reticular iron structure very similar to the Railway station bridge (Ponte degli Scalzi). The structure was formed by reticular iron beams, a structure of great relevance, but at the same time with low static efficiency, especially for the compressed beams, their evident undersizing and the following problem of load peak.In fact, after about eighty years of service, and partially because of the corrosion caused by the Venetian environment, in the 1930s the Accademia bridge, as well as the Scalzi bridge, were declared precarious.

MiozziIn those years a long debate started, several interesting projects were proposed. What in the end prevailed was the hypothesis of a temporary wooden bridge, designed by the senior official of the Technical Office of the City of Venice, the engineer Eugenio Miozzi.Miozzi proposed a solution of a single 48 m free span bridge, consisting of two arched reticular ribs, made by 4 cm thick wooden (larch) boards, held together by bolts and plates welded to obtain the necessary continuity. A mixed wood-steel structure of a great interest, especially because the lamellar techniques were in this period still being established. The arches were connected by a reticular system of wooden diagonals and metal tie-beams with turnbuckles.The large ribs were 2 m “high” at the supports, decreasing to 1 m at the keystone, also connected by a wooden reticular system and, again, tie-beams.To withstand the resultant of the bridge (about 260,000 kg the horizontal component, 200,000 kg the vertical component), Miozzi had to use both concrete foundation piles, and a crown of wooden poles (vertical and inclined). The poles could not be inserted by “hammering”, due to the vicinity of ancient buildings, so Miozzi invented a special process, unique to Venice, using wooden piles with screw-like metal tip.Basically because the dimensions of the bases, of the concrete and wooden piles, Miozzi managed to obtain a very low solicitation on the ground: 0.2 kg/cm2.After he settled the foundations problems, Miozzi worried about the failure of the wooden system and its joints. Miozzi proposed oak wedges – that were hammered “a forza” in keystones – in relation to the disarmament of the provisional ribs.The bridge was assembled between 10th December 1932 and 15th January 1933.

Maintenance worksA first series of maintenance work was done already in 1934 (re-painting with linseed oil and re-tightening of the nuts). In the following years the bridge needed no major maintenance. Only after the Second World War, was it decided to implement an important structural alteration: 4 steel arches – with the “wood around them”, connected by wooden diagonals, were realized in 1948 by Breda company. An imitation of the original structure designed by Miozzi, but less efficient in terms of lateral bracing.We still do not know how much the new structure increased the weight of the bridge (we assume a modest increase, however).In 1982 the bridge had new difficulties regarding its stability and, between 1984 and 1986, Jogna and Creazza, with Ballio and Turrini as consultants, designed a “new” temporary bridge that became an arch structure in metal and wood.

BRIEF HISTORY OF THE THREE “ACCADEMIA” BRIDGES IN VENICE

Università IUAV Venezia. Unità di ricerca “Arte del costruire” Umberto Barbisan, Marco Pogacnik, Luka Skansi

References:Ballarin M., Perché dovrebbero essere demoliti i ponti in ferro sul Canal Grande a Venezia, in “Ingegneria. Rivista Tecnica Mensile”, n.10, ottobre, 1926.Barbisan U., Venezia, il legno e i ponti, in “Tetto e Pareti in Legno, periodico dell’edificare con il legno”, n.13, giugno 2009.Barbisan U., Il legno: tradizione e innovazione, Forlì, 2008.Cosmai F., Sorteni S. (a cura di), L’ingegneria civile a Venezia, Venezia, 2001.Creazza G., Lettura critica degli aspetti statici nella trattatistica veneziana del Cinquecento, in AA.VV. (a cura di Manno A.), Cultura, scienze e tecniche nella Venezia del ‘500, Istituto Veneto di Scienze, Lettere ed Arti, Venezia, 1987.Miozzi E., Dal ponte di Rialto al nuovo ponte degli Scalzi, in “Annali Lavori Pubblici”, Roma, 1935.Populin E., Il ponte dell’Accademia a Venezia, Venezia, 1998.Siviero E. (ed.), Ponti delle Venezie, un percorso storico, Padova, 1996.

Fondo Miozzi, Archivio Progetti dell’Università Iuav di Venezia.

IABSE34th IABSE SYMPOSIUM - VENICE 2010

LARGE STRUCTURES AND INFRASTRUCTURES FOR ENVIRONMENTALLY CONSTRAINEDAND URBANIZED AREAS