Hanger bolts and solar fasteners in sandwich panels

For the energetic use of sunlit roofs, photovoltaic and solar thermal elements are mounted using different fastening systems on existing roof surfaces. For the installation on trapezoidal profiles or sandwich panels, hanger bolts and solar fasteners belong to the most prevalent fastening systems. For the structural analysis of these systems, however, only insufficient design approaches are available until up to date. Especially for the application on roofs covered with sandwich panels no design criteria is available at the present. The introduction of roof parallel loads from roof shear, wind and snow into the substructure can be specified as pressing problem. Within the scope of a research project sponsored by the DIBt (German Institute for Building Technology) design criteria for hanger bolts and solar fasteners in sandwich panels with a plastic foam core were developed. When roof parallel forces are applied to the fastener the fastener is supported by the sandwich panelsŽ surface sheet. For that reason the load bearing capacity of thin steel sheets with a thickness from 0.38 mm to 0.56 mm for different diameters of hanger bolts or solar fasteners is determined. ... mehrBeside the local hole load bearing capacity of the sandwich panel the load bearing capacity of the whole upper flange is from major interest. Performed tests show that an overloading of the upper flange results in cracks in the core material combined with a separation of the core material and the surface sheet. Because of the various designs and materials of sandwich panels the definition of a universal load bearing capacity is not possible. But when respecting some boundary condition relating to the material properties and the shape of the sandwich panel a conservative value of 0.70 kN can be used. Beside the already developed design approaches there are still open questions for further investigations. Among others this includes the mentioned load bearing capacity of the upper flange and the load bearing capacity for cyclic stresses.