GNGTS 2017 - 36° Convegno Nazionale

444 GNGTS 2017 S essione 2.3 Design philosophy and regulations. Glass facades are usually designed as constructional components aimed to resist ordinary loads only (self-weight, wind), while enhanced curtains are properly calculated and generally over-dimensioned for special structures only. There, appropriate safety levels are mandatory, especially if exceptional loads are expected. Glass fragments represent in fact a critical issue for people, hence cracking of facade panes should be prevented. For the seismic design of glass curtains, general EU standards for buildings can be taken into account (i.e. EC8 (2004)). There, however, secondary components only are considered and no regulations account for the curtain wall typology, or for anchoring systems, materials, etc. The building as a whole is only required satisfy specific inter-storey drift values. Distributed TMD concept. In this paper, unitized glass curtain walls (UCGWs) consisting of pre-assembled modular units, with insulating glass panels sealed to metal frames and fixed to the main building via rigid metal brackets (Figs.1d to 1f), are investigated under seismic events, with careful consideration for their role in the dynamic response of the buildings they belong. A novel design concept, consisting in a distributed TMD, is then numerically assessed. Based on such a design concept, glass curtains are actively involved in the dynamic performance of the enclosed building, with expected marked global and local benefits. The proposal takes advantage from the consolidated use of passive control systems in civil engineering applications, and specifically from the wide use in buildings of TMDs to wind and seismic loads effects (Lee et al. , 2006; Hoang et al. , 2006; Moon, 2016; Mohebbi and Joghataie, 2012), see Fig. 2a. Preliminary design. Assuming that the single UGCW modular unit is connected to the primary structural system by means of four corner brackets, special mechanical connectors are proposed to replace traditional restraints, so that the feasibility and potential of the distributed TMD concept could be properly assessed. The typical control system can take the form of a viscoelastic (VE) solid damper, consisting of two metal plates and a rubber layer (thickness h d and surface area A d ), see Fig. 2b and Bedon andAmadio (2017a, 2017b). The base plate is bolted to the inter-storey floor of the primary structure, while the UGCW frame is rigidly connected to a sliding plate, so to enable possible crushing and rotations of the VE layer when the UGCW panels are subjected to external pressures. Apreliminary estimation of the mechanical properties of such a device (stiffness K d and damping term c d ) can be carried out based on classical theories (Chopra, 2011), hence: and (1) (2) with M glass the mass of a single glass panel, ω 1,glass the operating frequency of the UGCWmodule, ξ the damping coefficient of rubber and c cr its critical value. For design purposes, a high damping rubber was taken into account. The fundamental period T 1,glass of the UGCWmodule, in addition, was set equal to the building period T 1 . Possible tearing of the VE layer was then prevented, through the parametric numerical investigation, by limiting its shear deformations: in [mm] (3) Case study building. An UGCW spanning from floor-to-floor was taken into account for the FE study (2.90 m×1.6 m the size of each module). The UGCW was assumed belonging to a 4-storey, steel frame building with residential destination (category of use ‘A’, based on EC1 2004), located in an earthquake-prone region of Italy, see Figs. 2c and 2d. Overall base dimensions of 10 m×20 m were taken into account, with 12 m the total height, 3×2 bays in the longitudinal and transversal directions. Inter-storey floors consisting of in-plane rigid, steel- concrete composite slabs were then considered. All the steel members, S275 grade ( f y =275 MPa and f u =360 MPa the yielding and collapse stresses), were supposed designed in accordance with EC3 (2004) provisions, based on permanent and accidental loads at the Ultimate (ULS) and Service (SLS) Limit States. Global dynamic effect of dissipative UGCWs. The overall dynamic effects due to UGCWs with VE fasteners was first considered. To this aim, eigenvalue FE numerical investigation were