TE Venice-Mestre Line: design, efficiency, innovation
Ten months of construction and 35,000 hours of night work were required to complete the mission entrusted to GCF by RFI: to reconstruct and enhance the Railway Electric Traction on the Ponte della Libertà, the historic translagunar connection that has linked Venice to the mainland since 1845.
Two inspiring criteria of the project developed by GCF in close collaboration with RFI Management and the Archaeological Superintendent, characterized by strongly innovative choices.
Firstly, to reconstruct the electric power line with criteria that make it not only more powerful, but also more resilient to the atmospheric aggression typical of the lagoon environment. Secondly, to prioritize an aesthetically sober and innovative design, more suitable for harmoniously integrating into the environmental and architectural context of a city like Venice, universally known for its beauty.
The innovative gantries used and the many solutions adopted - in the design phase, choice of materials, production processes - have not only contributed to better supporting the important and growing railway traffic, but also to give a new skyline to the bridge itself, transforming its 2,500 meters into an ideal sober and modern 'rail carpet', worthy of the city of art, canals, and... bridges.
The new contact line for the Ponte della Libertà
An innovation site to maximize functionality and aesthetics
Special RCK45 type concrete resistant to atmospheric and marine agents for the foundations; AISI 316 L stainless steel, resistance class S240, capable of offering excellent guarantees of resistance to the corrosive action of salt spray for girders, beams, and pendulums; and for the equipment, Omnia type aluminum alloy cantilevers certified for durability even in particularly aggressive atmospheric environments. The excellence of the material components was preferred to ensure stability and resistance to the new TE line of the Mestre – Venice S. Lucia railway bridge across the lagoon.
In parallel, the design choices, characterized by simplicity and innovation, have provided the aesthetic result, replacing the pre-existing, intricate support complex with an elegant design solution: the installation of 50 8-meter high and over 18-meter wide "T" gantries, placed in the center between the two railway bridges, which, thanks to their dimensions, are able to cover all four tracks of the railway route.
The result is simple and of unquestionable aesthetic value. Despite the magnitude of the numbers and weights handled in ten months by the "bridge construction site" to transform 30,000 linear meters of reinforcing steel into gabions, pour 1,000 cubic meters of concrete, handle and assemble 230 tons of steel, tension 20,000 meters of supporting cords and 20,000 meters of contact wire.
All this without ever interrupting or hindering railway traffic, which gradually saw the new gantries "above" the pre-existing line and, finally, without interruption, witnessed the demolition of the pre-existing structure and enjoyed the new 4 contact lines.
The new skyline of the translagoon railway bridge of Mestre - Venice S. Lucia
Renewal Works of TE on the Ponte della Libertà: the video
The different phases of work, from the pouring of the foundations, to the installation of modern gantries, to the fitting with Omnia System Cantilever, to the final tensioning.
The operational phases of the lagoon construction site
The preliminary check-up of the entire bridge
Four main operational phases have been organized for the construction works on the site, preceded by a careful series of experimental investigations aimed at assessing and certifying the overall health status of the two railway bridges: the old one, with single-span masonry arches, and the new one, consisting of reinforced concrete deck bridges.
An 'X-ray' check-up that has relied on the entire range of diagnostic tests: continuous core drilling mechanical soundings, sampling and analysis of bedding mortars, tests with jack to determine the stress state and mechanical and deformability characteristics of the masonry, extraction of concrete samples and compression tests, tensile tests on metal bar sections, use of a pacometer for qualitative investigations on the reinforcement of the reinforced concrete conglomerate.
Preliminary phases of construction of cages and reinforcement of blocks
The realization of the foundation blocks.
The replacement of about 500 reinforced concrete slabs (800 kg each) placed to connect the two railway bridges allowed to create solid bases on which to build the new foundation blocks, 74 in total, of which 50 intended for fixing the gantries and 24 prepared for the appropriate tie rods. Gabions of 4 x 4 meters, weighing 7 quintals each, consisting of 400 meters of linear 16 mm rebar, were placed in the appropriate formworks and fixed to the base slabs with stainless steel screws. Then, at a rate of 2-3 formworks per night, the casting and smoothing of the foundation blocks were carried out using about 10 cubic meters of RCK45 type concrete for each one, exposure class XS3, particularly suitable for its resistance characteristics to atmospheric aggression phenomena.
At the same time, approximately 10 km of polyethylene conduit for signaling cables and signaling power supply was laid along the 2,500 meters of the Ponte della Libertà.
Concrete supply, casting and shelling
The installation and testing of the new innovative gantries
"It was a particularly difficult and delicate phase," commented site manager Tiziano Bernardi, "given the size of the artifacts to be handled among the cables of the current overhead line, but the organization and harmony within the work team allowed us to carry out our task efficiently and, above all, safely, in compliance with delivery times and standards."
The phase of installation and on-site assembly of the new, innovative gantries undoubtedly represented an excellent performance for the GCF men who were called, in the midst of the nights of the lagoon winter, to fix on the innovative foundations V-shaped girders of 7.60 meters (weighing 1,700 kg) onto which to mount - maneuvering them among the cables of the existing TE - the enormous beams of 18.60 meters (weighing 1,850 kg each), each equipped with 4 pendulums of over 100 kg, designed to serve all 4 tracks with a single, large "T" made of 4 tons of special steel.
Overall, the operation involved the movement of over 230 tons of steel along the 2.5 km of the bridge..
Installation of stainless steel V-shaped girders: 8 meters in height weighing 1,700 kg
"The choice for the novel T-shaped gantries," explains GCF’s designer Engineer Michele Granzotto, "preferred over traditional structures, was dictated, like every design choice, by the need to combine aesthetic result and functional performance: being based on a single pillar, they could be placed in the center of the two railway bridges, in a position set back from the brackish water and, therefore, more protected from corrosive agents".
Insertion of the beams: 18.60 meters in length weighing 1,850 kg
The tensioning of the new overhead lines
After completing the setup operations of the gantries with 216 modern 'Omnia' type cantilevers - also preferred for their characteristics of high mechanical resistance and better performance in difficult environmental conditions such as those posed by the lagoon - the construction site, at the beginning of 2019, proceeded with the tensioning of the new 4 contact lines with an overall section of 440 mm² and fully adjusted conductors.
An important task that, in just 16 subsequent nightly tensioning sessions, allowed for the dismantling of the pre-existing lines and their replacement with enhanced lines anchored with 48 modern automatic tensioning systems.
A race against time (as well as, on some occasions, against adverse weather conditions...): an average of about 800 meters of new line constructed and replaced each night, thanks to the use of an extremely efficient tensioning train, with its 15 modular elements capable of maneuvering along the affected stretch, and thanks to the intervention of teams of specialized, cohesive, and trained workers, working in synergy.
A truly efficient mobile workshop, capable of disassembling old components, collecting hundreds of meters of ropes and wires, tensioning the new supporting cords and conductive wires, ensuring perfect sag and adjusting the tension of the new overhead line, and, after a few hours, promptly restoring the renewed overhead line to railway traffic, every morning at 5, already in operation.
The tensioning of the new overhead lines, at night and in conditions typical of the lagoon winter.
New Electric Traction: Technical Specifications
Foundation Blocks: n. 74
Dimensions: 490 x 490 x 50
Material: Concrete RCK45
Gabions: 400 linear meters of 16mm rebar
Contact Lines: 4 x 2,500 m
Supporting Cords: 20,000 m
Contact Wire: 20,000 m
Total Section: 440 mm²
Conductor Hangers: 2,400
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Girders: n. 50
Height: 7.60 m
Weight: 1700 Kg
Material: Stainless Steel AISI 316 L -
Beams: n. 50
Width: 18.60 m
Weight: 1850 Kg
Material: Stainless Steel AISI 316 L -
Pendulums: n. 200
Weight: 102 Kg
Material: Stainless Steel AISI 316 L -
Cantilevers: n. 216
Type: Omnia
Material: Aluminum Alloy -
Foundation Blocks: n. 74
Dimensions: 490 x 490 x 50
Material: Concrete RCK45
Gabions: 400 linear meters of 16mm rebar -
Plates: n. 500
Dimensions: 220 x 80 x 16
Weight: 800 Kg
Cover: 6 per base -
Contact Lines: 4 x 2,500 m
Supporting Cords: 20,000 m
Contact Wire: 20,000 m
Total Section: 440 mm²
Conductor Hangers: 2,400 -
Construction Site: 10 months
Hours worked: 35,000
Concrete: 1,000 cubic meters
Steel used: 230 tons
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