Structural design of insulating glass units: equivalent thickness of laminated glass, load sharing and internal actions

It can be said that at the present time in buildings most of glass elements are used as a part of curtain wall or simple window glazing systems; consequently, these glass types are defined as ‘infill panels’ that have a lower class of consequence with respect to main and secondary structure elements and do not contribute to the structural stability of the load bearing members. This research and its case studies focus on structural calculation methods and FEM-based design and analysis of laminated glass panes and insulating glass units (IGU) used as infill panels. Regarding the laminated glass panes, the study aims to investigate the stiffness family oriented shear transfer contributions of viscoelastic interlayer materials to the ‘equivalent thicknesses’ of laminated glass panes in terms of simplified calculation method of EN 16612:2019. Regarding the insulating glass units, this study aims to analyse the calculation methods provided by the same standard in order to obtain the load partition values of external loads and the effects of internal loads by taking into account the presence of gas within the glass unit cavities. Within the framework of case study, a wide variety of IGU options were analysed by preparing 3D FEM models in Autodesk Robot Structural Analysis, including ‘vertically/horizontally positioned, two edge/three edge/four edge supported, double glazed insulating glass units (DGU) with PVB/Ionoplast interlayers’ and ‘vertically positioned, two edge/three edge/four edge supported, triple glazed insulating glass units (TGU) with PVB/Ionoplast interlayers’. For the laminated glass panes, the equivalent thickness values were calculated by referring to the time and temperature dependent ω-shear transfer coefficients of the reference PVB and Ionoplast interlayers. External loads (wind loads, imposed loads, snow load) acting on IGU options were determined in accordance with the relevant Eurocodes and Italian technical standards, basing on assumptions. Internal loads given by the isochore pressures due to the cavity pressure variations of altitude, temperature and barometric pressure were determined by referring to standard IGU production and installation conditions mentioned in DIN 18008. Selected groups of load combinations were created in accordance with the “limit state design” rules by using the partial factors proposed by EN16612:2019 for glass infill panels. The deflection values obtained under SLS combinations were checked with the design values of deflection. The bending stresses obtained under ULS combinations were checked with the design values of bending strength. To do this, the design bending strength for heat-strengthened and tempered glass panes were calculated by taking into account the appropriate values of “load duration factors-kmod”. Finally, the results of FEM analyses performed for the structural models of all IGU options were presented. While the outputs of the case study analyses give tangible reference points to be taken into account for an optimal structural design of infill panel type glass elements, it is also expected that entire research study will contribute to the practical development of structural design of glass elements.