Platform on new construction, renovation, restoration and transformation
The Meelfabriek in Leiden is a large-scale transformation, redeveloping a monumental industrial building complex into a multifunctional residential area. The old monumental buildings are combined with new construction.
Pieters Bouwtechniek fulfills the role of structural engineer for The Flour Factory. The structural engineer designs - in close consultation with the architect, developer and contractor - the new structures and adjustments to the existing structures. For this, a thorough analysis of the existing structures is essential.
No building on the Flour Factory complex is the same. They were built in different times, with different building materials and systems. The 40-meter-high old silos are made of concrete with large dense concrete walls, and the Flour Warehouse consists of a completely open concrete column structure, while the Mill-Riffell building has a steel structure with wooden floors. A total of three new buildings are being created: a 3-story underground parking garage and two new residential towers. The remaining buildings are existing and will be transformed. The transformation involves rigorous work on the existing structures to allow for the new functions. Large holes in the concrete silo walls and closed facades are needed to turn a pitch-dark silo building or warehouse into a usable hotel or residential building, where sufficient daylight enters and the new residents can stay in a good living environment. New floors are being made in the silos for the hotel rooms. The closed facades of the old Meelpakhuis will be removed, after which the floors will be provided with balcony edges for the benefit of the loft apartments.
The challenge for the structural engineer is to enable the rigorous interventions without making the existing structures unstable and without causing excessive settlements. To this end, load-bearing calculations are made for both the old and new structures. It is important that the modifications do not become unfeasibly expensive.
Hundreds of archival drawings were searched, well preserved in the old vault of The Flour Factory. Still, parts were missing from the archive. Therefore, much measurement work and material research was done on site. What is the strength of the old concrete and steel? To what extent is the building cracked? Where is the reinforcement in the concrete? Is the chemical composition of the steel suitable for welding new steel to it? How high is the groundwater? Where are the load-bearing sand layers in the soil?
For all existing buildings, the existing pile foundations will be reused. Many are founded on wooden piles. At several locations, the foundation was excavated and the wooden pile heads were inspected to see if they are rotten, how much bearing capacity they still have and how long they will last. At all the buildings, the piles are still good except for the Boiler House, which dates back to the 19th century. There the piles are rotten and the entire foundation is being repaired with new piles.
Loft apartments are being created in the former Meelpakhuis. By recalculating the bearing capacity of the existing concrete skeleton and foundation, three new floors can be made on top of the existing building. The warehouse had a heavy function. A lot of flour was stored there and heavy equipment was used. The new houses are less heavy and this was exploited to add floors. Because the taller building catches much more wind, a new stability core is being created. Locally, new foundation piles are being added.
Meanwhile, construction of Phase 1 is nearing completion. Part of phase 1 was a 3-story underground parking basement that connects directly to the Mill-Riffell building, which is founded on wooden piles. Creating such a deep construction pit, right next to a national monument on wooden piles, is no easy task. All structures and implementation methods were meticulously calculated in order to create the more than 11 meters deep building pit, without causing damage to the adjacent buildings. A building pit with steel sheet pile walls and underwater concrete was used and the parking garage was founded on 476 screwed piles with a precast concrete core.
The design and construction team has been working on this complex project for over 6 years. Not to mention that before that, owner/developer Ab van der Wiel had spent almost 30 years preparing all the processes. And then the construction of phase 2 has really only just begun. This shows what is involved in transforming valuable cultural-historical heritage. Pieters Bouwtechniek considers itself fortunate, as an engineering firm, to be able to work on many monuments and transformations. The Meelfabriek is one of the finest projects on this reference list.
