Prefabrication is often suitable as elements based on steel sections and plasterboards are rather light and easy to handle. By prefabrication, excellent tolerances can be achieved which is a condition for good performance. An important advantage is that working from below is minimised.

In this project, different types of floors have been studied which, are described in the following Sections. Most common floors are based on load bearing C- or Z-profiles 150-350 mm deep, supporting a profiled sheeting and boards and insulated by mineral wool against sound. The ceiling consists normally of one or two layers of board screwed to profiled resilient bars who are fastened to the joists. The joists are sometimes replaced with a profiled sheet 100-200 mm deep. Different solutions within this range are presented in the following sections 3.2-3.6.

Prefabricated floor elements normally span across a single bay, while floors built on site may span two or more bays. The advantages with continuos spanning are increased stiffness and damping, the disadvantages are that vibrations may be felt in adjacent rooms and that flank transmission may increase.

For economy and flexibility in use it is important to be able to create as long spans as possible. To make the floor strong enough to carry the loads is no problem for reasonable spans. Also deformations can be limited. The challenge is to avoid unpleasant vibrations for dynamic loads. The first problem is that a light construction is much easier to excite than a heavy construction. As we do not want to make the construction heavy, the solution is to make it as stiff as possible for point loads. The other problem is that steel is very elastic and it does not absorb vibration energy well, which means that vibrations after an impact may be felt for a long time. The solution to that is to make the composite construction as energy consuming as possible. Within the project, different types of floors have been tested with respect to vibrations and methods to increase damping are studied in serviceability tests.

An obstacle is that there are many different criteria based on stiffness but no accepted standards for the behaviour of the floor in service state. Furthermore damping is not included in the criteria. Within this project, no attempts are made to establish such a criteria. However many measurements on vibration and damping were made, which were compared with subjective experience. It is proposed that every new type or variation of floor must be at least subjectively tested before being used in a real building.

Acoustic behaviour of floors also has been studied within the project, both airborne sound and impact sound resistance. To achieve good properties, it is important that the ceiling is attached by flexible fixings so that vibrations from the floor do not spread to the ceiling and that the floor is insulated with mineral wool. Down to 100 Hz light floors normally perform well. To achieve good performance at lower frequencies, the floor must not be too slender Also many other parameters that influence the acoustic behaviour.

Within the project, many tests were made on impact sound insulation. A theory based on these tests and earlier tests on wooden floors is established. The theory can be used as a guide as how to reduce impact sound and to predict the sound reductionvalues at different frequencies.

Sections 3.2 describes how fire ratings of REI 30 respectively REI 60 can be achieved with gypsum boards as protection from below for a standard type of light floor. The floors are both calculated with numerical methods and tested. That means that this types of light floors fulfil requirements and standards for apartments in all member countries, compare Section 2.

Section 3.3 describes laboratory tests on both airborne sound and impact sound for light steel floors. The achieved values fulfil current requirements for apartments in all countries. In the section also a theoretical model for prediction of impact sound is adopted and described for this type of floors.

Section 3.4 describes a large number of serviceability tests made on different types of light steel floors. Specially the effect of different forms of construction on stiffness for point loads and natural frequencies are studied, giving practical aid for the designer of this types of floors.

Section 3.5 describes sound insulation, impact sound and vibration tests of a floor in a real house. Vibration was also tested on a model floor with the same properties. The floor was of the same type as earlier described, but the top layer of gypsum boards were replaced with a thin concrete topping.

Section 3.6 describes tests of light elements and of floors built by a number of elements. A new way to reduce vibration by introduction of visco elastic dampers between floor and ceiling is developed and tested with encouraging results. Some of the vibration modes were eliminated. The work to try to eliminate the rest will be carried on.

In Section 3.7 design rules and recommendations that can be drawn from the work on light floors are presented in a summery.

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European Coal and Steel Community