GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 2.2 348 allow to maximize the structural performance of the coupled system. The hyperstaticity of the hybrid structure and the congruence of floor displacements would in fact manifest in internal moments (and thus progressive damage) of the RC beams. The exoskeleton is connected to the RC frame by rigid links at the level of each storey. The exoskeleton is designed as a rigid pinned structure composed of HE450B columns and HE360B beams (S355 the resistance class). In the case of MOD_02 the bracing system is composed of stiff X diagonal bracings at the 2 nd , 3 rd and 4 th floor (2×HEA300), that do not buckle and remain elastic. At the level of the 1 st storey, a single BRB diagonal is calibrated on the base of the input design seismic load. Fig. 2 (a) and (b) shows the deformed shape of MOD_01 and MOD_02. In MOD_01 the RC frame is deformed; its inter-storey drifts are due to the deformation of the exoskeleton and for this reason it can be damaged during an earthquake if the exoskeleton is less stiff. In MOD_02 the RC framemoves almost like a rigid body, as the exoskeleton is rigid in the upper floors and concentrates all the deformation in the 1 st (or ground) floor, where the RC frame is decoupled from the soil. Nonlinear static (push-over) analyses were carried out on the three models earlier described (under triangular load pattern for the in-plane seismic forces). The results in terms of force- displacement curves are proposed in Fig. 2 (c) . The introduced red cross points highlight the collapse for the plastic hinges at the base of the 1 st storey RC columns. It can be noticed that the base section of the RC columns (1 st storey) collapses at the same amplitude of lateral displacement d for MOD_00 andMOD_01, although the resistance of the bracedMOD_01 system is much higher. On the contrary, in MOD_02, no significant damage in the hinges of RC beams and Fig. 2 - Deformed shape of the first mode for (a) MOD_01 and (b) MOD_02 models (SAP2000). (c) Pushover curves (triangular load pattern) of all three models.