Stabilisation of beams by sandwich panels - new regulations and recent research results

Sandwich panels are modern pre-fabricated construction components used as cladding elements for different types of buildings. Sandwich panels consist of an insulating core material covered by two faces which are typically made of thin metal sheets. In standard applications, the panels are mounted and fixed on a load-bearing substructure of beams or purlins. Sandwich panels can reduce the problem of lateral torsional buckling of this substructure of beams or purlins by providing stabilization either by shear stiffness or by torsional restraint. The new edition of the German standard for the design of steel structures DIN 18800 gives formulae for the calculation of the stiffness of the torsional spring for restraint of the substructure under vertical downward loading. These new regulations are based on experimental investigations and parametric finite element analyses. These formulae only apply for sandwich panels with steel facings and polyurethane and mineral wool as core material. The paper explains the load-bearing mechanisms of the stabilisation effect by the sandwich panel. A mechanical model is developed for extending the range of application of the design formulae and to include the effects of creep and elevated ambient temperature. It presents the new regulations of DIN 18800 and explains the tests on which these regulations are based. The spectrum of applications not yet examined is investigated by tests and accompanying numerical calculations within the framework of the EASIE project. As a result of these investigations the torsional restraint of panels with facings made of aluminium and glass fibre reinforced plastics (GFRP) and with cores made of EPS are dealt with. The load case wind suction is discussed in addition. The increase of the torsional restraint obtained by fixing roof panels at the upper flange (which is mainly with saddle washers) is also explained and quantified by these investigations