The project was first announced in 2006 by the National Railway Infrastructure Management company, a subsidiary of the Greek Railway Authority. It involved upgrading the historic cog railway in Kalavrita in the north west of the Greek Peloponnese. The northern part of the Kalavrita valley is the location of the Vouraikos gorge that was cut by the river which runs into Corinthos bay.

The construction of this route, known as the Diakofto-Kalavrita cog railway, was carried out by French contractor Aton in 1896 for Greek prime minister Charilaos Trikoupis and his government. The route runs through the gorge next to river, and it served an area lacking road access until the late 1960s.

The first steam locomotives ran on coal, while today the train consists of two carriages and is powered by a diesel engine located in the middle. Even today, the track still contains rails that are marked with the date of their production. The entire route, including all facilities such as stations, stops, and a 20m-wide zone on each side of the track has been identified as a historical monument by Unesco and the Hellenic Ministry of Culture.

Today, the route is regarded as a unique tourist attraction in Greece, as well as internationally. Τhe entire length of the track, from Diakofto station to Kalavrita is about 22km and takes about an hour to travel. On the cog sections of the route, locomotives can travel at a maximum velocity of about 12km/h, and on the friction sections they speed up to 40km/h. At its steepest, the inclination of the track is some 17.5%, explaining why a conventional train could not travel on this route. When it was built, a cog straight-edge was fitted between the rails on three parts of the route, a total length of more than 3km. This cog straight-edge locks into a mechanism in the locomotive and enables the train to ascend to almost a kilometre above sea level at Kalavrita station where the route ends. Τhis cog railway has the narrowest track gauge in Europe, at 750mm.

Initially the route is smooth and after travelling through fields along the coast, it leads into the gorge, where impressive red rock walls eroded by water form the first narrowing of the route.

After passing through numerous tunnels, the train reaches Portes, where the train enters another tunnel at the narrowest point of the gorge. The tunnel still has heavy iron doors at its two portals; in the 1930s and 1940s these doors were only opened for trains to pass and remained closed at all other times to prevent pedestrians from entering the tunnel. After ascending the last section of cog mechanism, the train reaches the station at the delightful village of Zachlorou.

But the bridges on the route are currently being upgraded to allow them to carry bigger axial loads from new, heavier locomotives, and to improve their response to seismic events. The work, which involves the replacement of bearings and strengthening, started in May this year, and is expected to be finished before the end of the year.

Design of the bridge upgrading work was carried out by Greek consultant K Mylonas & Partners, whose engineers had to overcome a large number of technical obstacles, while at the same time providing a smooth and effective construction methodology for this unusual assignment.

The contract for the work was awarded to contractor Edraco, a subsidiary of Greek contractor Edrasis, in February this year. Edrasis area managing director Aristoteles Tsagkarogiannis and site construction manager Nikos Melikidis organised a multi-disciplinary team of staff and the logistics necessary to address all the technical and safety issues, in order to complete the works as quickly as possible. This was particularly important for the local economy, which would be seriously affected by the suspension of rail services.

Specialist subcontractor Elemka was appointed to carry out the upgrading work on the ten railway bridges, five of which are arch bridges and five beam bridges. Elemka’s expertise is in the inspection and maintenance of bridges, replacement of bearings and joints and so on.

The project had particular strategic importance because of its cultural significance and its role in the tourist industry. The difficulty of site access created by the local terrain meant that the only way to get materials, equipment and staff to the site was by the train itself. On top of this, the need for specialist technical solutions to accomplish the work required, all combined to characterise the project as a unique challenge in railway maintenance and bearing replacement.

Τhe steel bridges are either beam or arch structures, with subsidiary longitudinal girders that are reinforcements in three axes. All steel elements are connected using rivets and retaining plates.

Out of the ten structures, nine are single-span bridges ranging from about 10m length, to the longer arch structures of up to 26m span. The other arch bridge had three spans each 20m long, with a total length of 60m and a significant inclination of 10%.

Elemka’s engineers had to address the special technical requirements of each bridge as well the requirements of the design. More precisely, with the steel structure being more than 100 years old, the steel elements of the bridge might demonstrate the effects of fatigue.

Another issue was the very difficult access to the job site. At seven out of the ten bridges there was no road access and the only means of transport was the locomotive. This had a limited capacity for cargo, in addition to which it had to respect the dimensional limits of the tunnels and the cog mechanism, in terms of materials and machinery that could be transported.

One major problem that had to be addressed was the fact that no cranes or any other lifting equipment could be used at the jobsite.

The narrow route of the railway meant that there was no storage area along the route, not to store equipment and machinery. Hence the contractor used a platform that could run on the rails, as storage area. What’s more, the fact that staff had to operate in a dangerous working environment in a steep gorge, using safety harnesses and suspended working platforms meant that a safety engineer had to be in constant attendance. Another issue was the laborious and time-consuming process of demolition and drilling of masonry piers and abutments at the area where bearings were located.

As a result, Elemka had to develop a unique methodology in order to carry out the upgrading work while still meeting the requirements of the design. The company designed and built a special steel cantilever frame, which could be placed on the abutments. It had to be specially designed so it could be assembled and dismantled, transported and installed at the job-site without the use of any lifting equipment.

The resulting design was a steel frame consisting of 38 steel beams of various types (HEB 160-260), 56 connection plates and an enormous number of steel angles and bolts – some 980 bolts per frame.

Consequently it took more than 20 days to transport, assemble and install two steel frames at the job site. Another critical issue was the need for a total counterweight of 10,000kg per frame – and this was achieved using water tanks. Ten water tanks were used for each frame, filled with water that was extracted from the local river using underwater pumps. The idea of using any other type of anchors to connect the steel frames onto the abutments was out of the question, given that the stone-built abutments are more than 100 years old. Furthermore, abutments and piers were strengthened using steel bar anchors, a process that was carried out by UK specialist Cintec.

For all the reasons detailed, engineers decided to install the steel frames on top of the sleepers. The longitudinal as well the transverse inclination of the structures had to be taken into account in order to accurately level the steel frames.

Eight suspender wires were installed on the cantilever frames in order to raise the arch bridges off their bearings. The suspenders were formed of seven-wire strands of 16mm diameter, PC strand category 1670/1860 with a maximum working load of 224kN and a breaking load 260kΝ.

A methodology similar to that used for bridge post-tensioning works was applied to the structure – using barrel-shaped anchor systems with wedges to grab the strands in position and a jack to accommodate the tolerances of the settlement of the strand.

Two steel beams capable of carrying the dead load of the bridge were bolted to the underneath of the steel arches at specific points, close to the ends. By this means, the loads were transferred through the suspender wires to the steel frames.

Due to the age of the structure, and in order to assure the strength of the arches and their steel parts, four Alga tension bars were used, two at each end. These had a diameter of 17.8mm, with a maximum working load of 230kΝ and a breaking load of 255kΝ. The supporting steel beams were also designed to withstand the tension loads of the bars. In order to achieve the appropriate length for each particular bridge span, Algabar couplers were used.

This technique was used to avoid any tension in the arches, and eliminate the presence of any loads which could damage and deform parts of the steel bridge during the suspension and lifting process. The tensioning of both the wire strands and the bars took place using hydraulic jacks to apply tension loads specified by the design.

The lifting/suspension of bridges was accomplished by four hydraulic jacks which each had a capacity of 20,000kg, capable of carrying the self-weight of the steel bridge within a safety margin as specified by the design. Prior to the lifting process, an accurate elevation survey was carried out using laser measuring equipment, after which the sleepers, cog rails and safety rail lines close to the abutments were removed. The area near the joints was cleared of ballast and other debris, and the positioning of the superstructure was checked, under supervision of the site engineers before the lifting process was carried out.

The old bearings were so rusted and corroded that was impossible to dismantle them without using oxygen cutting equipment.

Elemka had to ensure against the possible failure of the hydraulic jacks, hence temporary bearings and supports were used. Τhe stone-built substructure was demolished to an elevation suitable to allow the installation of the new Alga linear steel bearings, which were either fixed bearings or longitudinally guided as required by the design. For the installation of the new bearings onto the steel superstructure, steel transition plates 30mm thick were used.

Once all the works had been completed, the bridge was carefully repositioned using the four hydraulic jacks. Reinforcement was placed and a wooden plywood mould installed to the same dimensions as the original stone–built substructure, to provide a new plinth for the bearings. The Greek Railway Authority had demanded that any changes to the original appearance of the structure should be avoided.

A primer was applied to the stone substructure before concreting; when the concrete had reached the required strength, the jacks were released and the bridge load was transferred on to the new bearings. Final elevation checks took place together with mould dismantling, cleaning and checking of the bolted connections to new bearings. Epoxy paint was applied, along with lubrication in order to eliminate corrosion problems and ensure they could be replaced easily in future.

Since the assembly, transportation and dismantling of the steel frames was a time-consuming process, the process of repositioning the frames from the abutments of one bridge to another, was carried out by sliding the frames on the railway lines. Steel girders and PTFE/inox plates were used for the sliding process, combined with certain safety measures to prevent accidents or damage to the frames during the operation. Steel wire ropes were used to restrain the frames while they were being lowered down the track.

This successful project can be seen as a pilot project for upgrading similar historic structures on the Greek railway network, and confirms that such structures can be made to conform with modern seismic requirements while maintaining their historic characteristics.

Sotos Raptopoulos is site maintenance & inspection engineer at Elemka

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