The structural design of insulated glass. The BAM method for the determination of the load sharing

Insulating Glass Units (IGUs), composed of two or more glass panes held together by structural edge seals, defining cavities filled by gas, are widely used in architecture thanks to their thermal and acoustic insulation properties. Their structural response is strongly influenced by the complex interaction between the glass plates and the air/gas, permitting the sharing on panes of applied loads, so enhancing the load bearing capacity. This effect, usually referred to as “load sharing”, is due to the pressure variation in the interpane cavities consequent to the applied actions, and depends upon the flexural stiffness of the panes and the gas compressibility. Furthermore, also changes in the barometric pressure and in the gas temperature inside the cavity, can unbalance the external and internal pressures, developing effects in all the panes. An accurate design of IGUs must necessarily take these phenomena into account. Here, several models for the calculation of IGUs, including the Betti’s Analytical Method (BAM), are presented. The model, that is going to be included in the new EuroCode on structural glass, allows to evaluate the response of IGUs composed of an arbitrary number of glass panes, under the most various support conditions and external loads, including line-distributed and concentrated actions. The great advantage compared to other methods is that it provides compact and easy to apply formulas, requiring coefficients that can be summarized in synthetic tables.