The new Police and Justice Centre – a colossus
The Police and Justice Centre (PJZ) in Zurich is an exceptional building. It will not only contain offices, but also a prison wing, a gym, a petrol station and a large entrance for articulated lorries. Accordingly, the building requirements are extraordinary, with its support structure having to be able to withstand a high load. This calls for unusual planning measures – and a unique manoeuvre on the construction site.
The foreman gives the first command to the two crane operators via radio. They set their machines in motion. The chains are slowly tightened, and the huge steel reinforcement floats above the ground. The dimensions of the 12-tonne monster are approximately 3 × 3 × 1 metre. The two construction cranes lift the reinforcement higher and higher – carefully observed by Marius Egger. He is a civil engineer at Basler & Hofmann, and he, together with his colleagues Tanja Pfeiffer and Sebastian Villiger, who are also on the construction site today, and many others planned the support structure of the new PJZ in Zurich. This also includes the huge steel reinforcement, which as part of this manoeuvre is to be positioned on a support made of reinforced concrete in the future first basement floor of the PJZ, like a mushroom cap on its stem. Together with Marius Egger, we climb onto the scaffolding to have the best-possible view. “The crane operators have to coordinate their movements extremely well to make everything work,” he explains.
One of the largest steel reinforcements in Switzerland
It is Wednesday, 5.30 p.m., and half an hour ago work finished at the construction site. The site of the new PJZ has long since emptied, and only the group of builders and planners responsible for the steel reinforcement is still on site. “For what we’re going to do, it’s better to have no one in the way,” says Marius Egger. Installing steel reinforcements isn’t that unusual in itself. They increase the support surface and thus allow the latter to better distribute the force with which it carries the ceiling and the floors above it. This prevents supports from piercing the slab under heavy strain. However, normal steel reinforcements are around 40 times lighter than the colossus used here at the Zurich PJZ, which took around 600 hours to produce. Usually, a reinforcement can be installed with a single construction crane. Performing this manoeuvre with two cranes and two operators is highly unusual and very tricky: the cranes must lift the heavy load in a precisely coordinated manner, transport it jointly through the air, and finally place it in an exact predefined position. “The whole operation is quite extraordinary,” says the civil engineer with some pride.
Delicate manoeuvre
For the manoeuvre, the team of builders have attached the 12-tonne colossus with chains to a horizontal steel strut, the two ends of which in turn hang on the hooks of the two cranes. Ideally, the steel strut should always be horizontal, so that both cranes carry exactly half the load of the steel reinforcement. At the moment, however, about three metres above the ground, the chain is slightly slanted. Marius Egger is frowning. “Not good,” he says. The more inclined the strut hangs, the more unilaterally the load is distributed between the two cranes, and the greater the risk that one of the machines will no longer be able to carry the weight. The crane operators need to correct things. The steel reinforcement swings in the air, while the steel yoke returns once again to a horizontal position. The operation is then continued, and the reinforcement floats higher and higher and moves in the direction of the support on which it is to be mounted.
Exceptional solutions needed
This tricky manoeuvre on the site of the former freight station in Zurich Aussersihl-Hard is necessary because the new PJZ is an extremely unusual building. Starting in 2021, the 280-metre-long and 115-metre-wide building will house police and judicial units, which are currently still spread across some 30 different locations. These include departments of the cantonal police, the public prosecutor’s office and the police sciences.
In addition, there will be a four-storey prison wing, an explosives room, the police academy including two dojos and a gym, as well as a petrol station. On the first basement floor, there will also be a large hall with enough space to manoeuvre for articulated lorries for supply and disposal, travel coaches of the cantonal police and emergency and special vehicles. “Because the building has so many rooms of different sizes, its support structure is also unusual,” says Tanja Pfeiffer, who helped plan the shell. The first basement floor with the lorry entrance was a particular challenge: due to the large space requirements, there is only space for a few supports, making the load that each support has to withstand all the greater. That is also why the main support of the first basement floor needs such a large steel reinforcement.
Centimetre precision
Meanwhile, Marius Egger is too far away from the action for his liking, so we descend from the scaffolding, hurry into the side wing, climb up the concrete stairs and finally, via a ladder, reach the formwork for the slab of the first basement floor. There, the support protrudes a few centimetres above the wooden planks – and the steel reinforcement is already floating above it. On the wood, a square painted in red marks the position onto which it should be placed. A handful of builders gather around the reinforcement, pushing and pulling the 12-tonne colossus to align it. Marius Egger also lends a hand. Perfectly aligned, the two cranes precisely lower the steel reinforcement onto the support.
He walks around the reinforcement, which protrudes far from the support, which is 60 centimetres in diameter. He checks the distance to the formwork below. The distance between the formwork and the reinforcement should be at least two centimetres on each side according to the fire protection regulations. Later, this gap is concreted into the slab together with the steel reinforcement, and it is precisely these two centimetres of concrete that are prescribed as its minimum covering. Marius Egger takes out his measuring stick. One corner of the steel colossus is a few millimetres too low, so the cranes have to lift the reinforcement again and rotate it 90 degrees. Once again, it is positioned centrally on the support, and once again Marius Egger checks the distances. Finally, he reports: “More than two centimetres everywhere.” Both the builders and planners are relieved, and nod to each other in satisfaction. Tomorrow, it will be the welders’ turn. They will connect the steel reinforcement with the support. For today, however, the last radio message goes to the two crane operators: «Okay, time to call it a day!»