GNGTS 2022 - Atti del 40° Convegno Nazionale

248 GNGTS 2022 Sessione 2.2 In this paper, a case-study glass envelope is taken into account and investigated towards the assessment of actual mechanical properties and load-bearing capacities for seismic (and multi- hazard) retrofit purposes. The attention is focused on the performance demand evaluation based on a possible harmonized framework and protocol resulting from the application of actual technical regulations for structural glass design and from the additional integration of in-field Operational Modal Analysis (OMA) experimental techniques for the Finite Element (FE), state-of-art numerical analysis. Reference performance demand and indicators. According to CNR-DT 210/2013, the interaction between a given glass structure and the whole building must always be considered, together with the local behaviour of the glass elements. The defined performance levels can be reached using design choices and construction measures that involve 1) the use of suitable glass types and sizes; 2) the use of intrinsically ductile systems or connecting systems with a ductile behaviour; 3) the use of connecting systems which guarantee the glass elements a) rigid rotation/translation inside the load- bearing structural system, b) suitable limitation of the stress level, towards the reference material strength. The SLV (Limit state for the safeguard of human life) must make sure that the system capacity is not lower than the demand. The performance demand is defined in terms of forces and displacements, therefore there are two types of verifications: 1) resistance calculations, where it must be verified that the glass can support accelerations induced by the seismic event, and 2) displacement compatibility assessment, where it must be ensured that the interaction between the glass element and the rest of the building is compatible with the presence of glass. In general, this interaction is considered to be satisfactory if, at the SLV, the construction vibration does not lead to contact with the glass element and, therefore, that there are no hammering phenomena. It must also be guaranteed that the glass and/or the connection can compensate the movements of the remaining part of the load-bearing structure during the pre- and/or post-breakage phases. Displacements of the building and in particular inter-storey drift caused by seismic actions are the essential parameters for the design of glass panes, under SLV conditions as well as for the Damage Limit State (SLD). In general, these derive from the structural analysis of the building for the various limit states and performance levels required. The glass structure designer must consult these data in order to size the joints and connection systems of the glass elements with respect to the characteristics of the rest of the structure. Analysis of a case-study system . The structural system object of study consists of a steel- glass envelope built in 1961, as a composition of glass panes and a grid of steel mullions and arched transoms (Fig. 2(a)). The facade belongs to the so-called Information andDocumentation Centre (CID) museum, which is located in Torviscosa (Udine), see Fig. 2(b) and (Santi et al. 2022). The particular aspect of this system is presented by its shape (circle facade concept) and by its size (approximately 7 m of diameter), compared to the thickness and load-bearing capacity of single components (Fig. 2(c)). Glass elements are in fact shaped to follow the overall arched path and are characterized by simple monolithic (and relatively small) total thickness, compared to the covered surface. Moreover, steel members are reduced to a minimum (Fig. 2(d)), to preserve the transparency of the facade. The present study took a major advantage from in-field experimental investigations carried out in Spring 2022 to achieve some important geometrical and mechanical characteristics of the envelope (Fig. 2(e)). From a geometrical relief and OMA vibration investigation,