Florence, a floating platform for analysis at Ponte Vecchio before restoration

In Florence , the floating platform with scaffolding has arrived on theArno River that will enable the start of preparatory work for the restoration of Ponte Vecchio. This is an unprecedented construction site because never in its 100-year history has the bridge undergone a conservative restoration. Ponte Vecchio, in fact, has no stability problems, it is firm and anchored, but it accuses problems typical of any artifact placed outdoors, subject to weather phenomena and river flooding. Now for the first time it will be the subject of a complex restoration operation with the aim of enabling its complete enhancement.

“This is,” explained Mayor Dario Nardella, “a historic project because never has Ponte Vecchio had a restoration operation of this technical complexity. The work will cost more than two million euros and will be spread over two summers, when the water in the Arno is lower. Now the diagnostic part begins and then there will be the actual restoration, all entirely financed with municipal resources. This Bridge is the symbol of our heritage, it has withstood floods, fires, the Nazi-fascist invasion. Now it will be ’taken care of’ with a very scenic restoration that I am sure will attract the curiosity of Florentines and tourists. In the end we will have an even more beautiful bridge than we are used to seeing.”

The necessary platform will be used to carry out the surveys, the installation of the bridge monitoring system (which will last one year) and the sampling of materials, a fundamental service for the design of the restoration. These are therefore preparatory activities that will be carried out by qualified contracted companies identified under the Global Service. In fact, the platform will be used by the employees of the contracted laboratories and will remain positioned within the riverbed for about three weeks, barring unforeseen events and adverse weather conditions, moving from time to time from one span of the bridge to another according to the timing needed to carry out the specific investigations and sampling of each span, pile and abutment. The platform will be moored with the help of two concrete cubes near the left bank and, throughout the construction period, will be moved by a small tugboat both for survey needs and in case of an orange or red weather alert. During the operations, which will go on for three weeks, the platform will be held in place by four anchors, placed upstream of the Old Bridge.

The structure assessment and monitoring activities that will be carried out can be summarized in the following steps: inspection and visual diagnosis of the bridge structures; geometric survey of the structures and the ongoing cracking phenomena using laser scanner and drone; processing of photoplans and thermographic and Ultra Violette surveys of pier arches, abutments and wing walls; elaboration of a suitable model for the identification of the monitoring parameters of the structure; installation of the monitoring system for a period of 12 months that will allow to monitor the significant structural parameters related to the arches and other main elements of the bridge; elaboration of periodic reports on the monitoring progress; elaboration of a final report on the annual monitoring data and their interpretation also with the help of numerical modeling; management of a web platform and alerts in case of sensitive events.

Then, the struts of the stores above the bridge will be subject analyzed to recognize the wood species, measurement of wood moisture, survey of sections, classification according to strength, analysis of biotic degradation with resistigraphic surveys. Again, material tests aimed at surveying and mapping the health status of the various surfaces of the bridge (arches, abutments, armillae, vertical walls of piers, abutments, etc.) will be carried out. With regard to the arches, the survey will identify not only the geometry and stratigraphy of the various materials constituting the structure, but also the possible presence of deteriorated areas.

There will also be a georadar prospecting from the surface, a search that includes staking and topographical survey of the investigated surface and of the extremes of the crawls performed with a biantenna system including georadar spreads on both the extrados and intrados surfaces of the bridge. Further analyses are also planned including an underwater survey and bathymetric survey along the perimeter of both piers and both abutments of the Ponte Vecchio, in particular a visual survey will be carried out by a diver equipped with all the necessary equipment to verify the state of preservation of the foundations of the piers and abutments of the bridge. The inspection will be performed both visually directly by the diver and with a high-definition underwater camera and video camera. Also planned is a multibeam survey at the entire development of the Ponte Vecchio both upstream and downstream of it in order to verify the presence of any significant changes in the bottom of the riverbed since the last bathymetric survey carried out by the City of Florence in 2015.

Also on the agenda are the assays of the bridge’s driveway road superstructure in paving with the aim of detecting the stratigraphy of the pavement, of any waterproofing layers (or of the arrangements used for this purpose) and of the fill and backfill material up to the structure of the arches.

Restoration

The restoration work will work on color alterations, the presence of algae (so-called “black crusts”), lichens and weed vegetation, inconsistent surface deposits, and fractures and cracks in the pietra forte. All moisture stains in the soffit of the structure, on the abutments and on the piers will also have to be removed. It will begin with biological disinfestation and then proceed to the consolidation of the damaged stone and the reconstruction of the missing parts of all components of the bridge, from the vaults to the piers to the sub-arches and parapet. Special attention will also be given to the parts decorated with coats of arms and selvages, which are now difficult to read. Degraded wooden parts (so-called struts) supporting the stores will also be fixed with woodworm treatment and painting. Finally, work will be done on the roadway with joint stenciling and protective painting of the pavement, also in order to avert any possible percolation of rainwater inside the artifact.

The first interventions will take place in thesummer of 2023, starting with the rehabilitation of the stone pavement of the superstructure by providing for the replacement of the deteriorated and broken stone slabs with slabs of the same type and laying of the breathable protective coating on the stone pavement. It will continue with interventions concerning the piers, abutments and wing walls (preliminary interventions, preconsolidation and cleaning, consolidation and doweling, grouting and final treatments) consisting in particular of: elimination of infesting vegetation and biological patina; stitching and sealing of micro-cracks in the walls by injection of appropriate and suitable materials; reconstruction of masonry areas with masonry integrations, joint restrengthening and reinforcement of detached and/or cracked masonry blocks (stone) (also through reinforced seams after sealing of cracks by injection of appropriate materials); breathable protective treatment of the structures.

In thesummer of 2024, interventions will concern the arches with cleaning, reconstruction of missing or detached parts, reinforcement of detached and/or cracked masonry blocks (stone) also through reinforced seams, mortar injections in the present cracks, breathable protective treatment of the structures; it will continue with interventions regarding the elevations of the artwork concerning the patching and sealing of the micro-cracks present in the walls through the injection of appropriate and suitable materials, reconstruction of the masonry areas with masonry integrations, re-straightening of the joints, breathable protective treatment of the structures; and finally the restoration of the supporting struts of the goldsmith stores.

Florence, a floating platform for analysis at Ponte Vecchio before restoration

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