P 1185 – Application of hot dip galvanizing on temporary bridges for the German Railway
DB Netz AG uses temporary bridges with different spans and construction methods during temporary construction work on and alongside railway lines to intercept the tracks. The service life of the bridges is generally between several days and a maximum of three years. The need for auxiliary bridges is great, as many bridges need to be repaired at present and in the near future and numerous new ones are to be built. The corrosion protection currently used consists of an organic coating, which often has to be repaired due to high mechanical stress caused by assembly and transport in order to avoid corrosion damage such as under-rusting or pitting and the associated weakening of the material. In addition, a high repair rate is associated with high expenditure and resource consumption.
Hot-dip galvanizing is a well-known corrosion protection system, with high advantages concerning durability and stability. With research results of the last few years on the influence of hot-dip galvanizing on fatigue strength the basis for an application under cyclical load was also created. It was found that although the application of hot-dip galvanizing has a negative effect on the fatigue strength of steel, this only results in a reduction of up to one detail class for the design. Based on these results, this short study examined whether the application of hot-dip galvanizing is possible and useful on Deutsche Bahn temporary bridges.
The different boundary conditions of the bridge systems of the construction types “twin girder temporary bridge” and “small temporary bridge” as well as boundary conditions to be considered for hot-dip galvanized constructions, such as galvanizing lengths or weights, hanging-points and ventilation openings were examined. From this, hot-dip galvanized variants were developed for some temporary bridge systems and examined for load-bearing capacity, fatigue and serviceability according to current standards. It was found that even a recalculation of the designs according to the current Eurocode standards would lead to adjustments as the used type statics were partly established in 1990.
From a design point of view, especially the twin girder temporary bridges with spans of 9.60 m and 12.00 m can be hot-dip galvanized. In addition to supplementing ventilation and flow openings, the end crossbeams have to be adapted and all drill holes must be increased by one millimetre due to possible zinc deposits.
A galvanizing of main beams with a span of more than 12.00 m was considered problematic due to the lamella-reinforced design of the structures and large component lengths or weights. Although the classification of the temporary bridges as temporary structures means that proof of fatigue strength in accordance with Guideline 804 is not required, an estimated service life of 50 years has been proofed for the galvanized twin girder temporary bridges.
An application of hot-dip galvanizing for small auxiliary bridges of the type KHB-KW depends on the galvanizing possibility of the cross girders, which should be checked on basis of previous test galvanizing without additional ventilation holes. However, it was not possible to achieve a fatigue life of 50 years for the cross beams of the small temporary bridges, which was not exclusively due to a hot-dip galvanized design. All investigations and results are presented in detail in the report using the example of the twin girder temporary bridge ZH 9.60 m. The other systems investigated are summarised in the appendix.
Finally, the hot-dip galvanized auxiliary bridge constructions were also considered economically, whereby the low initial costs as well as a reduction or even avoidance of maintenance and renewal measures could be emphasized. As a result, the application of hot-dip galvanizing for twin girder temporary bridges, especially in the span width range up to and including 12.00 m, was found to be economically viable.
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Prof. Dr.-Ing. D. Ungermann, S. Holtkamp M.Sc., M. Ant M.Sc.