Screw-jacking and moving the Nooitgedacht flour windmill

New homes have been built around the “Nooitgedacht” flour mill in Spijkenisse. However, no permit would be issued for the new construction project unless it included adjustments to the windmill. This is because a windmill always has the right to ‘catch’ wind, according to the laws of windmill biotopes. By “raising” the windmill, the sails can catch enough wind for the windmill to do its business.

Client:
Molenmakerij Herrewijnen
Location:
Spijkenisse
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Project

Strukton Infratechnieken was asked to jack up the windmill seven metres and to build a concrete cone in the space thus created. In addition, a two-metre deep cellar was built under the cone.

The windmill is situated between a private residence, a shed and a pet shop. Because the new body of the windmill would have been larger in diameter than the current body due to its cone shape, it would not have fitted between the abovementioned buildings. The solution was to move the windmill a distance of approximately two metres.

The windmill was transferred to the sliding/hoisting structure using the ‘chair method’, where recesses were made in the brickwork into which steel profiles, called ‘chairs’, were positioned and cast. 

Immediately beside these chairs, a new recess was then made in the windmill wall. Horizontally positioned lifting beams were inserted through these recesses, which were then used to raise the windmill. Around the chairs and the lifting beams, a reinforced concrete beam was poured, called the ring beam. This ring beam ensures that the reactive forces in the lifting beams are spread evenly over the brickwork.

After the windmill was shifted the two metres, it was screw-jacked, including the spiral chute and everything else. This screw-jacking procedure was carried out with four screw-jack towers. Instead of hoisting screw-jacks under the spiral chute, it was decided to use a hoisting system with tension rods. The windmill was therefore screw-jacked and suspended on eight rods. The screw-jack towers were positioned on temporary column bases on piles.

When the screw-jacking was finished, a new pile foundation and a concrete floor were realised under the windmill. The cone of the windmill was built up on this foundation using prefabricated concrete segments. After the segments were poured, the windmill was lowered with screw-jacks and the shifting/hoisting structure was removed.