Basic research on fixing elements: drawing up universal design guidelines for high resilience mechanical jointing techniques for insulation products

Status

finished

Summary

The project deals with the different possibilities in the design of fixing elements. Both the method of fixing insulants to walls and the technique used to fix elements to insulants are essential to the question of whether such jointings will be generally used and to the convenience of usage.

The research carried out into relevant literature gives a comprehensive overview of the current state of these technologies. The mineral wool and polystyrene foam insulant systems seem to be highly favoured at the moment, with a 95% share of the market. Development of alternative materials leaves all possibilities open, though. Various dowel systems are currently predominant for the fixing of insulants onto the facade, but there is also some use of profile fixing systems. Besides mechanical fixing onto the facade, insulants can also be stuck to it. Purely mechanical fixing occurs only in a few exceptional cases. A series of unconventional fixing systems and elements are to be found in patent literature and are partly also published in specialist literature. These will be dealt with separately, as they show great potential for evolution and encourage the development of even more new ideas. Where insulants are used as lost casing, high demands are made on the fixity of the insulant and the mechanism of force application through the fixing element because of the extent of the load they have to bear. Different commercially available systems are described in published literature. Various fixing systems between outside-casing and inside-casing currently are used.

The following conclusions can be drawn from the systematic analysis of the options described: insulant fixing always comes up against the same problems. Forces should be applied to the non-stiff, non-fixed insulant as gently as possible and without stress peaks.

Plans for experiments are drawn up in the project. These were reached after investigating the current state of technology, systematically dividing the field into different areas of work and theoretically analysing different approaches. Experiments involving simplified geometrical properties or simplified frictional contact will be carried out preferentially. The results will be continuously verified by comparison with theoretical models and the results from simulations.

The sphere of the practical experiments is essentially divisible into three areas. The first group of experiments is used for the determination of material properties. Using material science research methods, parameters are determined for the insulant which will later be used in theoretical models for the design of fixing elements.

In the second experiment group, basic construction geometries of the simplest possible design are elaborated and used as fixing elements. Their behaviour during application of a mechanical load is tested. This step should help to increase understanding of the fundamental behaviour of different solutions to the fixing problem. The results are used in conjunction with the material properties determined in the first experiments to develop simple design models.

The experiments show that the influence of the material properties on extraction forces can be approximately predicted. Moreover, the evolution of empirical models on the basis of material properties and geometrical parameters is possible. The introduction of reduction factors due to stress peaks is necessary, however.

In addition to the basic analyses of simplified geometries, more complex geometries taken from existing solutions for fixing elements are tested. This step makes it possible to verify whether the results from the simplified geometries can be transferred.

In the third set of investigations, field wall systems are analysed. The investigation concentrates on the useability of fixing elements for lost casings. A brick element is used in the inner casing of the building. On the outer side, EPS with a density of 30 kg/m³ is used. Load occurs through the pressure of concrete during filling. The fixing elements withstand the pressure in the case of moderate concrete compaction and when concrete of K4 consistency is used. During filling the pressure of the concrete is measured by a suitable experimental assembly. As a result, the real load of the elements can be calculated.

In the third investigation field wall systems are analysed. That wall systems are cut into pieces with concrete cutting devices to analyse the quality of filling. At present acoustic investigations of the walls are carried out at Institute of Building and Industrial Construction at Graz University of Technology.

The Project is not yet finished. This summary refers to the interim reports and therefore, does not include last findings. Investigations still follow in wall mounting and clarifying pull out tests. However, the previous findings have brought essential results that are already used product design.

Contact

Dipl.-Ing.Reinhard Hafellner
Zentrum für angewandte Technologie
Peter Tunner Straße 19
A 8700 Leoben
Tel.: +43 (0)3842 47044-15
Fax: +43 (0)3842 47044-78
E-Mail: reinhard.hafellner@unileoben.ac.at