Issue 48

M. L. Puppio et alii, Frattura ed Integrità Strutturale, 48 (2019) 706-739; DOI: 10.3221/IGF-ESIS.48.66 710  Reduced costs. In the original consolidation project connections between the bracing system and the structure were made with threaded bars having a diameter of 16 with a pitch of 50 cm. In this case the connections are replaced with steel profiles with variable sections. Dissipative links The dissipation of seismic energy through the yielding process of steel elements has been studied by experimental approaches to evaluate the advantages of including this type of element in the structure. The study conducted by Jun Jie Li in 2010 [21] is an interesting example: it investigates the interaction between heavy precast cladding units attached to steel framed buildings. Usually designed as non-structural components, the cladding system may be used to reduce the response of the primary structure under seismic actions with the insertion of flexible connections. In fact, the panels are usually bound at the primary structure with connections used to transfer the vertical load alone. These also restrict the movement of the panel. Tieback connections, instead, are flexible connections which only restrict out of plane deformation and allow vertical and horizontal displacements. The hysteretic behaviour of the connection is inserted in the model with the aim of maximising the dissipated energy. This can reduce the damage of the primary structure during the seismic event. The results show that by using elastic-plastic connections we obtain a reduction of the damage caused by the seismic action (between 96% and 100%). Another interesting study concerns the seismic consolidation of the "C. A. Pizzardi" Hospital (unit D) in Bologna [22]. The analysis concerns the structural dynamic assessment of the existing structure, composed of a central non-moment- resisting steel frame characterized by a low horizontal stiffness, which supports essentially the vertical actions, and two external lateral-resisting elements of reinforced concrete (concrete cores) which mainly support the horizontal loads. The corresponding storeys of the two portions of the building (i.e. the frame structure and the lateral-resisting elements) are linked with specially-designed metallic sinusoidal elements (Figure 8). The effectiveness of the elements has been valued considering two resistant sections M1 and M2: the element with section M2 has a double stiffness in comparison to the element of section M1. At the beginning, the elements with a larger section (M2) are placed between the 1st and the 6th floor, and the elements with a smaller section (M1) between the 7th and the top floor. Various positions of the connecting elements were also tested to better investigate the contribution of these devices to the global response. Non-linear dynamic time-history analyses were performed. Fig. 9 shows the comparison between the different link configurations. Figure 8: Axonometry of the connection between the frame structure and the lateral-resisting elements [22]. Figure 9: Trend of shear at the base: comparison of different types of height arrangement of connection links [22]. The study shows that the connection link arrangement affects the stress reduction factor. Considering the solution with M2 only, there is a 30% reduction of the stresses (shear) and, at the same time, there is not an excessive increase in relative displacements. 0,50 1,00 1,50 2,00 2,50 3,00 3,50 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45 0,5 Shear at the base [t] x 10000 a [g] Trend of shear at the base M2 only Assessment M2 Higher Floors, M1 Lower Floors Rigid Links