Kingspan’s insulated roof and wall systems load span tables allow the designer to select suitable panel(s) and steelwork support spacing(s) for specific project applications.
Research carried out in the UK and Europe by Universities and Research Institutes since the initial development of insulated panels have established reliable design principles to predict their performance by calculation. Following this work the European Convention for Constructional Steelwork (ECCS) published in 1991, Preliminary European Recommendations for the Design of Sandwich Panels (Document number: 66) which establishes practical design methods.
Limit state analysis takes into account normal wind and snow loadings and includes the following factors which must also be considered for insulated roof and wall panel systems. These are:-
Temperature Loading
Thermal expansion of the outer and liner sheets will be different as the inside and outside surface temperatures vary. As the insulation core is bonded to both faces, this differential expansion causes panel bow. This can effectively reduce the imposed loads needed to reach the permissible stresses or deflection, so temperatures must be taken into account when calculating permissible loads.
Surface temperature depends on external coating colour and the following design values have been used:
Light colours 55°C
Medium colours 65°C
Dark colours 80°C
The load span tables are based on the following temperature combinations:
External winter roof temperature is taken as 0°C as it is assumed to be covered in snow for the worst load combination. External summer roof temperature is taken as 65°C as only medium and light colours are recommended for roofs.
Creep
The insulation core is a thermoplastic material which will slowly distort under long-term loads. Panel deflection, therefore, may continue to increase gradually under constant loading. This is known as creep.
Roof panels can develop creep under prolonged periods of dead loads and snow, however, wall panels are not subject to creep because there is never any long-term load, which affects the core. In the UK snow is not considered as a long-term load and is ignored, but creep due to dead loading is taken into account by reducing the shear modulus of the core (G) to 0.125 x G.
Load Combinations
Component self weight, snow, wind and temperature loads are considered individually and together in their worst combinations with appropriate load factors in order to determine the allowable imposed loads for the load span tables.
In these combined loadings the following load factors have been used for ultimate and serviceability limit state parameters to create the most correct in use conditions. These are generally in accordance with the ECCS Design Recommendations, but adjusted by Professor J.M. Davies from the Department of Structural Engineering at Manchester University, to allow for UK climatic conditions.