Repair of the Koehlbrand Bridge Stay Cable System
The Koehlbrand Bridge is a structural steel stay cable bridge with a main span of 325m and two side spans of 97.5m each. The 88 fully locked stay cables are anchored at the bridge deck and at two 98m high pylons.
The superstructure consists of a hollow box girder with slightly slanted webs. It is 17.8m wide and crosses the harbor area on Hamburg’s Elbe island Wilhelmsburg at a maximum height of 58m.
During the course of regular inspections by the Hamburg Port Authority (HPA), damage to the stay cable coating that made repair work necessary were repeatedly found. During the most recent inspection, coating and corrosion damage were found on eight stays. Consequently, the owner decided to carry out comprehensive repair on the bridge.
As the Koehlbrand Bridge represents the most important connection to the Hamburg harbor, closing of the bridge for the planned repair work was ruled out. Due to the stay cables’ alignment and geometry, scaffolding would have been a complicated and cost intensive alternative for accessing the bridge stays.
As a result of the positive experiences during the repair of the Kehl-Strasbourg Bridge (cf. DSI-Info 17, S. 28-29), the owner contacted Alpin Technik and Ingenieurservice GmbH and DSI. The two companies presented a proposal that was accepted after internal assessment. In order to test the suitability of the method as well as the DYNA® Protect System under difficult conditions on the Koehlbrand Bridge, the assignment for the first section was made in 2009 for the eight stays with the worst damage. These stays have diameters between 65mm and 120mm and a maximum length of 164m. On the whole, approx. 290m² of stay cable surface had to be protected.
Due to the good results achieved in the work on the first section, the owner decided to also assign Alpin Technik Leipzig with the corrosion protection of the remaining 80 stay cables as well as with the accompanying services (visual and magnet inductive tests).
The complete contract was awarded in September 2009. Following visual and magnet inductive tests of the stay cables, the stays were wrapped, with DSI supplying the necessary corrosion protection system - DYNA® Protect.
Both for the corrosion protection of new, fully locked stay cables and for the replacement or strengthening of the corrosion protection of existing stays, a wrapping with butyl rubber tapes offers the following significant advantages compared to conventional coating:
M A T E R I A L
practically impermeable for water vapor and oxygen
long lasting material and color
S Y S T E M
based on the DENSO corrosion protection technology that has been field-approved for decades
robust system thanks to a layer thickness of approx. 2.6mm and to exterior polyethylene carrier foil
formation of a tube like, dense coating due to self-acting cold amalgamation of the corrosion protection tapes in overlapping areas
no complicated surface preparation methods such as abrasive blasting are necessary
positive visual design aspects due to the colored external polyethylene carrier foil
adaptation to stay cable deformations thanks to the elastic and plastic characteristics of the wrapping
tolerates the discharge of stay cable filling additive without any flaking or crack formation
nearly maintenance free
DYNA® Protect Corrosion Protection System
The corrosion protection system consists of two layers of butyl rubber tape, each of which is wrapped around the stay at an overlap of 50%. The total thickness of corrosion protection is approx. 2.6mm and therefore five or six times as much as a coating. In the overlap area between the single layers, the butyl rubber compound adheres by cold amalgamation that is caused by an interdiffusion of the rubber molecules. This creates a locked, tube like and mechanically robust wrapping that is practically impermeable to water vapor and oxygen.