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tHe FLat FLOOR PLateS
the calculation of the strength of the plates
The mobile loads were calculated in accordance with the norms speci ed in Eurocode 1.
The loads exerted on each of the different oor levels of the build- ing were calculated to re ect the interior layout of the nal design. With knowledge of the mobile loads and the weight of the slabs (concrete and reinforcing) on the one hand, and the permanent loads ( oor nishing, carpets, technical infrastructure, light parti- tion panels) on the other, it was possible to calculate the moment distribution.This calculation was then used to draw up the rein- forcing plan.
the calculation of creep
Following the strength calculations, the stiffness of the oor plates was also calculated. After a period of time, concrete displays creep, which results in de ection or sag that is two to three times greater than the initial distortion. Large de ections over a longer period are not acceptable.
This gure shows the distortion of the plate over time. Certain areas of the plate will distort too much.The limit for the de ection of a plate is a maximum of 1/500th of the span between two axes.
Various measures can be taken to limit this sagging. Firstly, the concrete plates in the most critical areas should be cast with an adverse slope of 20 mm.This slope is achieved by setting the formwork at a higher level. however, it is also important not to remove the bracing (lateral supports) too soon.The sooner fresh concrete is subjected to load (i.e., is unsupported), the worse
the creep problem is likely to become.This unsupported loading should be avoided as long as possible.The temporary supports should remain in position under each other on each oor level of the building: i.e., the bracing continues right down to ground level. The combination of these measures, including the limitation of user load during the implementation phase, should limit the creep phenomenon within acceptable bounds.
the internal enlargement of the building
half way through the construction of the shell, it was decided that an additional 1,000 m2 of oor space was required.This decision had serious consequences for every aspect of the building. But it was here that the concept of a at-plate oor structure proved its value. It was no problem to pour additional concrete slabs, so that it proved possible to continue working almost without interrup- tion.The edges of the existing concrete plates were roughed up, additional reinforcing rods were chemically anchored into these exposed edges, and the additional square metres of concrete slab were simply poured alongside.
Integrating the technical infrastructure
Concrete core activation – responsible for cooling the building and a crucial element in its energy management system – was integrated in the concrete slabs.
The use of a at-plate oor structure has implications for the installation of the technical infrastructure.The necessary uniform distribution of force throughout the plates means that subsequent drilling – either during the construction phase or at any other phase during the building’s life cycle – is not possible. Conse- quently, it is important that the positioning of the concrete core activation and the conduits for all the technical facilities
(supply and discharge of water, ventilation, electricity and data)
is determined during the study phase and before the implementa- tion phase.
During the nishing phase there was a problem with the concrete core activation: a leak was discovered.The concrete slab in ques- tion was opened over a limited area, the leak sealed and the slab repaired.This incident shows that the delicate concrete core activa- tion system, even though it is enclosed within the concrete slab, enables the easy tracing and repair of any potential problems. Various access hatches in each slab also make it possible to check and alter the pressure in the pipes of the core activation system for each zone.