ABSTRACT
There are a lot of challenges during the life of engineering structures on the railways. The bridges, tunnels and culverts are getting old and they need very special attention. Even though the end of their service life seems to be over, it is smart to consider all alternatives. Rebuilding is not always the most economical solutions.
Of course the aging and the deterioration of structures is a big problem for old structures. Also the higher demands for current use often exceed the design criteria of old bridges.
The safety issues of maintenance have also much greater focus than before. There has happened and is happening changes in maintenance organizations and the responsibilities of maintenance vary. Today the knowhow of maintenance personnel is very important and difficult to determine into tenders, especially as the infrastructure has a mix of both old and innovative new structures and materials.
The management requirements to do the right actions at the right time, Of course the ultimate goal is to have the maintenance cost to a minimum and get as much value for your money you invest in bridges.
On the railways, especially in Finland with a great number of one track lines, it is very difficult to repair and maintain the bridges and the tunnels with any traffic disturbances. But this is always the main goal for these actions. Another major goal is to use methods to minimize cost in a difficult economic situation, execute without risks and maximize the effect. This is why Finland has very many innovative solutions to extend lifetime of railway bridges and tunnels instead of using heavier actions on bridges.
Old steel truss bridges are a huge problem in Finland, as the current loads exceed the design load to up to 20%. Also heavy mixed traffic has caused fatigue problems. There are several innovative methods to strengthen bridges without renewing them.
The problem is that the joints and rivets of these steel truss and girder bridges show signs of possible fatigue problems and failure. The first lighter method is to change the broken rivets into bolts. The strengthening by replacement is done under traffic without any traffic disturbance. The goal has been to lengthen the use of these old bridges.
The more advanced method used is to replace the secondary girders with new girders without renewing the main girders or trusses as the usually are strong enough for heavier trains. Old wooden sleepers have a age in 25 years to a point, that they are difficult to maintain and causes frequent maintenance needs. By replacing the wooden sleepers with a steel frame and measuring the rail into place decreases the need for maintenance to minimun. The steel frame also strengthens the secondary girders of the bridge or the girders can be replaced completely.
Transition zones are very problematic for the trains and difficult for maintenance, especially on old bridges. Soft soils on river beds or very high track embankments are difficult to keep in shape.
On old bridges, instead of building enforcements, the ballast is laid down with higher quality demands. This is proven to be a very efficient and practical way to decrease the amount of maintenance needed.
Other innovative ideas include the use of sliding rails to take out rail expansions joint that are very problematic for maintenance of track on bridges.
For concrete bridges of course waterproofing is very important, and a waterproofing of bridge decks has to be done in days instead of weeks. This is a big goal for us in Finland. Also the reinventing the edge structure to narrow bridges has many possibilities.
For tunnels all inspections can be done automatically and with no chance for human error, the accuracy and the repeatability of visual, thermal and 3D imagery is efficient. The goal is to find something similar for the bridges, the future is already today.
