Kraanbrug Maintenance

July 11, 2021

Every year we do maintenance on the Kraanbrug in the Naarden Fortress. Every year sees Monumentenbezit sees to it that this bridge in Naarden, at Fort Ronduit, remains operational.A specialized company is fully inspecting the bridge and carries out test runs. That way we can be sure that everything is still working properly. And that is quite unique, since very few crane bridges have stood the test of time.

Every year we do maintenance on the Kraanbrug in Naarden. The crane bridge was invented by the railroad engineer Frederik Willem Conrad. He had an important role in the construction of the first railroads in the Netherlands. To cross the many waterways in the railroads, he had to invent a simple and inexpensive bridge. This became the Kraanbrug. He first published a description of this in 1844. Over the years, the construction of the bridge and the material used changed, so that larger spans could be made and heavier equipment could drive over it.



Test runs for inspection of operation


Slangen Staal B.V.




Video on the maintenance of the fortifications of Naarden

Operation of crane bridge
However, the principle of operation did not change. The movable part of the bridge consisted of girders, on which rails were mounted. The girders were supported by a console or a diagonally placed strut. By means of a vertical axis, the girders could be turned to the side, opening the passageway in the bridge. Railroad sleepers were not used in the bridge, so turning them away was very easy.

The crane bridge in fortification construction
The Kraanbrug was also used in fortification construction. The reason, besides its easy operation and cheap construction, was that it did not obstruct the fields of fire and allowed defenders a clear view. An opened drawbridge does obstruct the view and can be used as cover. This is true of bridges in the fields of fire as well as those at the fortifications themselves. Crane bridges or remnants thereof can still be found at Fort Vuren and Werk aan de Diefdijk. There was one at Fort Honswijk. In Naarden, no less than four crane bridges were built. Two in front of the Utrechtse Poort, one in the access road to Fort Ronduit and one at the entrance to that fort itself. This bridge still exists and, thanks to the restoration a few years ago, it is fully functioning again. It remains special to see the bridge in operation.

More information about the monument the fortifications of Naarden? Then click here.


Also read about our other projects