Principal: Canton of Zurich Public Works Office
Contractor: Marti AG, Zurich, Anliker AG, Emmenbrücke
MEVA systems: MevaDec slab formwork
Engineering and support: MEVA Schalungs-Systeme AG, Seon, Switzerland
A new crime-fighting centre of excellence is under construction at the site of Zurich's former Aussersihl-Hard railway goods yard. Uniting functions currently scattered across 30 locations, Zurich's new Police and Justice Centre (PJZ) will house the cantonal police force, the prosecution authorities as well as police detention and prison facilities.
The building's diverse occupancy types, which include office accommodation, sports hall, shooting range and prison space, are also reflected in the structural shell. "The biggest challenge was the complexity of the project," explains Project Manager Paul Bühler from the Marti Group. "The many different types of space made finding a rhythm harder than, say, on an industrial scheme with typically recurring structures." Some 6,200 m² of the flexible MevaDec slab formwork were used to cast the large slab areas. The works had to be overseen by two general foremen working in tandem.
Fast and reliable
In casting the floor slabs, due consideration had to be given to the different space types and states of construction. Key factors, apart from the complexity of the floorplans, included the higher live loads imposed during on-site operations and the prescribed 28-day reshoring period. "Detailed planning was therefore vital in guaranteeing safety and the rapid progress of the works," says Dirk Sieber from MEVA's Engineering department.
Early stripping after seven days
The formwork was precision-designed with due allowance for the fresh concrete weight. Early stripping of the slabs, using the MevaDec drop head system, was possible after around seven days when the concrete had achieved adequate compressive strength. The patented drop head allows the slab formwork to be lowered by 19 cm and the removal of beams and panels for use elsewhere. The props, however, remain in place to support the slabs up to the end of the reshoring period.
Reshoring over several levels
Additional reshoring was, however, needed at certain locations to prevent possible deflection and cracking induced by premature initial loading. It was necessary to distribute the weight of the fresh concrete over a varying number of slabs, depending on their age and design load-carrying capacity. "Some of the upper-storey slab areas are thicker than on the underlying levels," explains MEVA engineer Volker Götz. "This meant that, in some places, completed slabs required additional propping before we could even install the formwork for the storey above."
"The exception is the rule"
Other special measures were necessitated by the building geometry. "Given the countless variations on this project, the exception is the rule," reports Dirk Sieber. "In one cycle, for instance, an obtuse angle coincided with a 5 cm split level. Elsewhere, the diverse occupancies entailed beams of varying thickness." MevaDec allowed all these exceptions to be accommodated by a single system. The slab formwork provides for the combination of several methods, thereby vastly minimising filler areas, even with convoluted floorplans. Project Manager Paul Bühler was more than satisfied. "No significant effort was needed for adaptation work. What particularly impressed us on this large project was the low onsite inventory made possible by early stripping."
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