Laminated glass (LG) is a composite solution for building applications and requires dedicated calculation methods to account for cross-section features, geometrical parameters, ageing effects, operational conditions, load combinations. Major issues for its safe design are associated by demanding performance requirements, both for glass members and restraints. Existing design standards, however, are still weak. The Service Limit State (SLS) considers the uncracked LG element subjected to characteristic design loads and assesses its deformability towards conventional limit values. The Ultimate Limit State (ULS) considers the LG element subjected to extreme values of external actions, and verifies that stress peaks due to the most unfavorable combination are lower than glass design strength. Rules are more rigid for the Collapse Limit State (CLS), which considers the LG element partially fractured. This need derives from the intrinsic brittleness of glass, and from the possibility of spontaneous breakage of one of its constituent layers. CLS must thus verify that the fractured LG element can guarantee appropriate load-bearing capacity for a suitable fraction of design ULS loads. Operatively, CLS verifies that the damaged LG element preserves suitable residual stiffness and resistance, when deprived of one glass layer. Accordingly, the LG element is usually oversized to guarantee cross-section redundancy, which includes one sacrificial glass layer in the typical layout.
Such a roughly simplified design approach derives from lack of robust engineering knowledge on complex mechanisms that typically take place in the post-breakage stage, and on the way to calibrate harmonized calculation methods to account for them. The post-breakage response of LG elements depends in fact on multiple influencing parameters, such as the bridging effect between glass shards and bonding polymers. Cohesive delamination, controlled by different characteristic lengths, can be described with models that are typical of laminates and has severe effects on the residual LG performances. Post-breakage is also severely affected by a combination of additional parameters, such as glass-interlayer adhesion, interlayer stiffness, load amplitude and strain rate, size/shape of glass fragments, etc.
HOPgLAz will develop a new holistic formulation for the post-breakage performance assessment of LG elements with partial damage, under different section properties and material compositions, loading features, ageing condition. A formulation will be proposed to quantify the mechanical parameters of fractured LG sections, and safely described their post-fracture residual capacity. This will provide strong advancement in research knowledge, as well as powerful tools on the side of mechanical design and fulfillment of fail-safe design principles.