Dynamic modeling of explosion-resistant glazed sytems

This thesis condenses the dynamic modeling of blast resistant glazed façades. A theoretical point of view is assumed and the problem is approached at different levels. For applications involving impulsive loads, laminated glass is usually employed so that an equivalent ductility is achieved and the risk related to the projection of fragments is reduced. These composites are made of glass plies, which are coupled by the cohesive action of polymeric interlayers. To this purpose, suitable structural models are introduced and numerically tested for both beams and plates. Fractional calculus (differential equations involving fractional derivatives) is adopted to describe the viscoelasticity at the level of the interlayer. As a main advantage, only two parameters are needed to define the relaxation function for commercial polymers. The comparison with the classical method, relying on an expansion in Prony series of the relaxation law, further highlights the simplifications obtainable with fractional approach. Since glass is a brittle material, there are few possibilities to significantly improve its resistance against blast loads. Therefore, one can employ dissipative devices to interpose between the panels and the back structure: the energy released by the load is partially absorbed by sacrificial (crushing) elements. This is theoretically demonstrated with reference to a paradigmatic problem. The dissipative unit is composed of a movable piston in unilateral contact, on its two opposite sides, with shock absorbers capable of plastic deformation, which are activated respectively during the compression and suction phase of blast load. Through a parametric analysis, criteria are proposed for the optimal design of such dissipative unit. The proposed technical solution is compared with a linear viscous dashpot, which is not as efficient as the previous one in limiting the effects of the first compression phase, but it can considerably reduce subsequent oscillations. A hybrid device, where viscous dampers and crushing components are integrated in parallel, seems to represent the best compromise. From an engineering perspective, it is important to asses the load-bearing capacity of the whole glazing system instead of the sole panels. As guide for structural design, a simple analytical model is proposed. The rear structure is represented by a pre-tensioned cable connected in series with a spring element; while each glass panel is reduced to a nonlinear oscillator via to Rayleigh’s method. The model allows to tune the inertia and the stiffness of the back structure. Generally, a compliant back structure allows an optimal absorption of energy and, consequently, preserve the panels. As a related problem, regulations provides also for testing procedures that define the capacity of glazed surfaces to withstand against soft-body impacts. These impulsive actions are concentrated on a small area, which dynamically changes according to the deformed shape of impacting body. The pendulum test is first analyzed with a simple approach based upon an equivalent linear and nonlinear 2-DoF system. The time history analysis is complemented with energetic considerations that, with reasonable assumptions, can directly provide the maximum stress in the panel through an equivalent static load. Moreover, a finite element tool has been developed. The comparison between the predictions of the proposed methods with that obtained from experiments and other advanced software, indicates the accuracy of this engineering approach and its range of applicability.