GNGTS 2018 - 37° Convegno Nazionale

374 GNGTS 2018 S essione 2.2 non-structural metal frame was hence designed along the edges of each glass panel, to keep the AN layers in position. Within the full walkway of the central nave, the LG panels have variable dimensions (depending on their location), spanning from 1.35×1.35m (G1-type), up to 1.45×2.65m (G2-type). While the G1-panels are point supported via mechanical restraints, major structural uncertainties are related to the bending performance of G2-panels, being supported along the short edges and spanning over ≈2.65m (Fig.1(b)). To limit the deformations of the roof, a bracing system was originally planned, with pre-stressed steel tendons (10mm the diameter). The tendons were designed to ideally half the span of G2-panels, but contact mechanical interactions were only provided between the mid-span restraints and the upper glass panels, hence resulting in temporary supports (Fig.1(c)). After the realisation of the walkway, in fact, long-term phenomena partly minimised the benefits of initial pre-stressing loads. Actually, the walkway suffers also for other degradation effects, being related to a combination of time, unfavourable ambient conditions (i.e., high relative humidity) and fatigue phenomena (i.e, continuous dynamic loads due to visitors). A non-destructive experimental campaign was hence planned in late 2017 (Fig.1(d)), so as to assess the effective dynamic characteristics and vulnerability of the structure. Structural design requirements. Generally speaking, glass roofs must be checked - under service loads - towards maximum deformations and stresses due to permanent and human induced live loads (including snow and wind effects, for outdoor structures), see (CNR-DT 210/2013). In service conditions, vibrations of glass roofs should be also properly limited, being Fig. 1. - Aquileia glass walkway: (a) general view, with (b) edge support and (c) bracing tendons for G2-type panels; (d) test setup.