Products and solutions, 2007-07-25, 11:04 AM
Single-handed bridge refurbishment
The now completed restoration of an 80 meters long railroad bridge in Torgau, Saxony, called for hard graft and masterly coordination of the various trades. Acting as general contractor, ThyssenKrupp Xervon refurbished the more than a century old steel structure single-handedly – taking care of steel construction, corrosion protection and all the necessary scaffold erection, track building and masonry work.
When Sächsische Binnenhäfen Oberelbe GmbH (the company responsible for Saxony's Oberelbe inland port) awarded the extensive refurbishment contract to Xervon last October, it was difficult to gauge the actual scale of damage to the Torgau Bridge. Apart from minor partial restoration in the Nineties, the filigree steel structure above the Schwarzer Graben, the old moat around the 19,000-population district town, had not undergone any kind of overhaul. It wasn't until refurbishment got underway that the corrosion damage beneath the layers of paint accumulated over decades was brought to light.
The all-inclusive bid submitted by Xervon not only comprised all the affected trades, i.e. the removal of the old track and laying of the new one, the erection of preparatory and accompanying scaffolds inclusive of their enclosure, refurbishment of the masonry on both abutments and the central pier, the replacement and reinforcement of damaged steel bridge components and subsequent application of anti-corrosive paints. Xervon's maintenance specialists also proposed a pretty unconventional approach in order to quickly ascertain the true scale of the required work. The roughly ten meter tall steel structure was not blasted a section at a time, but liberated of its old coatings over its entire length in one go (standard of cleanness SA 2). This way, it was possible to inspect and assess in detail most of the damage before the start of refurbishment.
However, before refurbishment could get started, the track had to be removed and the entire bridge had to be scaffolded, enclosed dust-tight and ventilated – to protect the environment and the work. "This way we could have carried out refurbishment swiftly even in a hard winter," says Xervon project manager Lutz Fischer explaining the relatively elaborate site preparations. Although prolonged low temperatures and snow didn't arise, Hurricane Kyrill did sweep across the construction site in January – without causing any damage to the scaffold or its enclosure. "You've really got to hand it to the scaffold erectors," exclaims refurbishment expert Fischer, who was in overall charge of the site.
The steel construction specialists – an external partner company with which Xervon has been cooperating successfully for years – then managed to carry out their work without any delays, despite the inclement weather. They removed and replaced every irreparably damaged element of the riveted bridge structure and reinforced numerous steel parts until they were satisfied that the bridge would be equal to the stresses and strains of the coming decades.
Restoration of the masonry on the two abutments and centre pier was initiated concurrently. The strategy drawn up by the Xervon maintenance team envisaged carrying out as much work as possible simultaneously. "This way we were prepared beforehand for all eventualities and were able to adjust our schedule accordingly," Lutz Fischer explains. As it turned out, the steel constructors had to eliminate considerably more damage than the client had originally expected. This took extra time and would have turned the progress schedule for the various trades upside-down if alternative measures hadn't been planned in advance.
Elaborate corrosion protection
By comparison, subsequent corrosion protection work proceeded entirely on schedule. When the steel constructors had completed their work on the first sections of the bridge, the corrosion protectors started applying the coating system a section at a time. This was a grueling task. Although the 1,600 square meters of surface area of the Torgau Bridge requiring coating was not a great deal, the bridge structure consists of highly intricate individual elements with countless rivets and bolts, which all had to be coated with extreme care.
Before applying the multi-layer anti-corrosive coating, the refurbishers first had to blast the treated section of the bridge again – this time down to the bare metal (SA 2.5). Immediately after this, an 80 µm coat of zinc phosphate primer was applied. Then the exposed edges were given special treatment. The paint for this is always applied manually with a brush so that all the edges, rivets and poorly accessible places are protected in the long term from corrosion. Two 80 µm intermediate coats of epoxy resin, the sealing of all gaps and joints with a sealant, and a final 80 µm topcoat completed the new anti-corrosive system on the Torgau Bridge.