The clever connection makes all the difference
The ceiling can bear loads in two directions and span greater distances. In the Pi project, the elements are up to 9 meters long, but the principle is also suitable for spans of more than 15 meters. The structure weighs about 30 percent less than concrete slabs and is significantly thinner than conventional composite structures. At the 80-meter height of the Zug project, this allows for, among other things, an additional floor and a significantly smaller foundation.
How were these improvements achieved?
A key factor in the Pi project is the 14-centimeter gap between the 6-centimeter-thick subfloor—made of so-called “construction beech” produced using veneer lamination technology—and the 8-centimeter-thick concrete deck. The two layers are firmly connected by a 60-centimeter grid of steel tube couplers. The gap ensures that the two layers—like the flanges of a steel section—are located far from the center of gravity, which increases the resistance to bending. The space itself is filled with insulation material as needed. In Zug, this is rock wool due to fire safety requirements.
How did this development come about?
The project was initiated in 2015 by Implenia Holzbau. They were looking for a composite floor that offers the properties of concrete floors without sacrificing the advantages of wood. We contributed the structural engineering concepts. The group led by Prof. Dr. Andrea Frangi at the Institute for Structural Analysis and Design at ETH Zurich tested the anchoring of the steel tubes in the wood and, through experiments, verified the stiffness and load-bearing behavior of the structure, thereby establishing the design basis. EMPA contributed by conducting sound measurements of the entire structure, including the subfloor. Where do you see other potential applications for the system? Because it enables larger spans—similar to those of flat concrete slabs—the ceiling is a viable option wherever great flexibility in room layout is required, such as in office buildings, public administration buildings, schools, or even in buildings with many stories and a highly varied mix of residential units. Its use begins where conventional wooden ceilings reach their limits. The system can be adapted to the specific requirements of each building by varying the thicknesses of the three layers—wood, air gap, and concrete—as well as their properties and the number of pipe connectors.
